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IntroductionNow face masks are necessary elements during the COVID. In practice, they are intended for one-time use, and to a large extent, it is environment unfriendly. Also during a shortage, repeated use is inevitable and it is necessary to have a disinfection mechanism. During the ongoing SARS-CoV-2 pandemic, hospitals, medical centers, and research institutions implemented different disinfection methods for these masks, usually involving ultraviolet germicidal exposure (UVGI) or some kind of heating methods. Nevertheless, these methods are not suitable for many ordinary people. What’s more, due to shortages, the reuse of these masks has become the only option. There is evidence that SARS-CoV-2 still exists on the surface of surgical masks even after 7 days, so the demand for feasible mask disinfection methods has further increased. Here will introduce a special device to do that.Introduction: Understanding the CoronavirusCatalogIntroductionⅠ Disinfection Device Production InstructionsⅡ Device Design Processes2.1 Device Size2.2 Thermal Test2.3 Box Lid Design2.4 UV-C System2.5 Making the Mask PlacementⅢ Set Up Arduino and Sensor3.1 Arduino Overview3.2 Material3.3 Sensors Installation3.4 Arduino Control3.5 AlarmⅣ Using GuideⅤ Temperature Cycle5.1 Heat Inactivation of Viruses5.2 Security ConsiderationsⅥ ConclusionⅠ Disinfection Device Production InstructionsThe device aims to create a low-cost portable device that can effectively use UVGI and dry heat to disinfect masks carry SARS-CoV virions, and can be easily operated by those who need it.Device Setup DiagramFigure 1. Device Setup Diagram1) The temperature must be kept within 65±5℃.2) The lamp must provide UV-C wavelength. UVC bulbs that emit very short ultraviolet wavelengths from 100 to 280 nanometers that damages the DNA of bacteria, viruses, and other pathogens. You should be careful, ultraviolet C is the most dangerous type of ultraviolet light in terms of its potential to harm life on earth.3) The duration of the disinfection cycle is at least 30 minutes. Because coronavirus is more sensitive to heat. A temperature of 56 degrees can kill the coronavirus within 30 minutes. So no more than 30 minutes to avoid potential mask degradation and function losses.Figure 2. Device Operational DisplayFigure 3. Device Physical ViewⅡ Device Design Processes2.1 Device SizeFigure 4. Device Size2.2 Thermal TestFigure 5. Thermal Test DiagramFigure 6. Test with ThermometerFigure 7. Test Boite Temperature Manufacturing of heating system:1) A frying pan with a diameter of 22cm (induction compatible) without handle.2) Cover the frying pan with aluminum foil to reflect UV-C light.3) Make a 20cm hole in the center of the bottom surface of the box.4) In order to maintain the position of the frying pan, please use four metal brackets as shown in the figure.Figure 8. Frying PanNote: The frying pan should not close to the wood of the box because it will reduce the thermal efficiency. Therefore, you must select the appropriate hole diameter and shape the metal bracket according to the following figure:Figure 9. Frying Pan Installation Diagram 2.3 Box Lid DesignFigure 10. Box Lid Design2.4 UV-C SystemFigure 11. UV-C LampFor the UV-C source in this device, it is an 11W bulb from household aquarium. As shown in the picture, the UV-C bulb is taken out and installed on the top cove. The installation method of the bulb is to make 4 holes in the top cover, and use the cable tie/cable tie and soft cushion to fix the bulb firmly. And the top surface is covered with aluminum to reflect ultraviolet radiation.You can feel free to use UV-C lamps from other sources. However, if you cannot access the crystal tube (used in this project), please do not use glass as a substitute, because glass will block ultraviolet radiation.2.5 Making the Mask PlacementThe mask will be placed on top of the metal frame. The I wire frame is made of thin copper wires, and each wire has 30mm spacing apart. The wire stand is located 120mm above the bottom surface. Next secure the wire racks together by passing the wires through the small holes on the front and back surfaces of the box.Figure 12. Mask PlacementⅢ Set Up Arduino and Sensor3.1 Arduino OverviewFigure 13. Arduino Overview3.2 MaterialArduino UNO Rev3Grove Basic Shield V2, 0Infrared temperature sensorLight SensorPush ButtonPiezo SpeakersFour-digit LED DisplayAdapter power supply DC 12V3.3 Sensors InstallationFigure 14. Sensor Introduction3.4 Arduino ControlINIT: In this state, the LED display indicates the temperature, but you have to wait for it to reach the threshold (70℃) before starting cycle counting in the COUNT state.Count: The number of minutes from 30 to 0 is displayed on the LED display next to the temperature digits. Additionally, in the case of too low temperature, or if the UV lamp is turned off, the status will change to ERR.END: This is the normal state at the end of the elapsed time. The speaker will remind. Press the button to enter INIT again.ERR: This is an error state, if the temperature is too low or the UV lamp is turned off, it will run. In terms of it, repeat the last step above.Code Download: LED Backpack Libraries and Arduino Wiring.3.5 AlarmIn fact, there are few alarm conditions. If the alarm is on, there will be a specific sequence on the speaker and a message will be displayed on the screen.Alarm condition: If the system is in ERR state (mentioned above) or the temperature is too high (over 75℃).Figure 15. Alarm System Diagram Ⅳ Using Guide1) Put the box on top of the induction (or resistance) stove.2) Turn on the power of Arduino.3) Close the box and start heating at 70~80% of the power of the induction cooker.4) Wait until the temperature reaches 60℃, and then reduce the variable power of the induction cooker to 30%.5) Now you can open the device, put the mask in and close it.7) Press the button to start, the remaining time (30 minutes) should be displayed.8) From now on, you need to wait 30 minutes, and there will be a signal on the speaker.9) If you want to restart a new cycle from the initial state, just press the button.Note: When the timer is counting the elapsed time, the dots between the Timer and Temperature displays will flash at 1 second intervals. Ⅴ Temperature CycleFigure 16. First Heat CycleFigure 17. Cycle with Opening-Closing 5.1 Heat Inactivation of VirusesSince the time of Pasteur, people have known the ability to remove microorganisms through moist heat, usually below 100℃. In this device, we implemented dry heat, which is reported to be effective in eliminating the infectivity of SARS-CoV. The analysis showed that the virus is largely inactivated within 30-90 minutes at 56℃, almost completely inactivated at 65℃ in 20-60 minutes, and at 75℃ in 30-45 minutes. In addition, a recent study showed that SARS-CoV-2 will lose all its infectivity at 56℃ after 30 minutes or at 70℃ after 5 minutes.According to these evidences and additional considerations regarding the effects of these disinfection methods on the function of the mask, we decided to set the heat exposure of the protocol used with the equipment to 65℃/30 minutes.5.2 Security Considerations• UVC radiation is harmful to human skin and eyes, so the UVC bulb should only be turned on when the box is completely closed.• Be careful with the metal parts of the box, they may be very hot after heating and may burn your skin when you touch them directly. Ⅵ ConclusionTaking into account the collected evidence and the technical details of the equipment, we decided to set the disinfection protocol to UVC irradiation for 30 minutes and 65±5℃ dry heat. In addition, the time required for the device should reach the required temperature and light intensity, which must be calculated. Using these specifications of UVC or heating alone should be sufficient to eliminate almost all SARS-CoV-2 infectivity, and the simultaneous action of the two should increase the effectiveness to reach a safer level.According to the available scientific evidence, the disinfection program may eliminate almost all SARS-CoV infectivity and will certainly make the masks safer to reuse than without any disinfection. However, it is designed in good faith and to the best of professional knowledge and ability, but the following must be stated:The use of this equipment to inactivate SARS-CoV-2 has not yet undergone proper laboratory testing, and it is impossible to confidently confirm the actual impact on the filtering capacity of the mask in advance.

Executive Summary: What is a Phototransistor?A phototransistor is a light-sensitive semiconductor device that converts incident light into electric current while providing internal gain amplification. Unlike simple photodiodes, phototransistors utilize a bipolar junction structure (NPN or PNP) to amplify the signal, making them highly effective for optical switching, object detection, and encoding systems in modern 2026 electronics.Ⅰ Introduction to PhototransistorsThe phototransistor is a specialized semiconductor device engineered to detect light levels and modulate the current flowing between the emitter and collector based on the photon intensity it receives.While both phototransistors and photodiodes serve as optical sensors, the phototransistor distinguishes itself through high sensitivity attributed to the internal gain of its bipolar transistor architecture. As of 2026, this intrinsic amplification makes phototransistors the preferred choice for applications requiring robust signal detection without complex external amplification circuitry.Ⅱ Video Tutorial: How Phototransistors WorkVisual learners can understand the practical operation of light detection in the following tutorial.Phototransistor Tutorial Phototransistor Video Description:A comprehensive tutorial demonstrating how to utilize phototransistors for precise light detection in circuit design.  Ⅲ What Is a Phototransistor?A phototransistor is an electronic switching and current amplification component that operates by converting photon energy into electrical signals. When light strikes the exposed base-collector junction, a reverse current flows proportional to the luminance intensity.Widely used to convert light pulses into digital electrical signals, these components are powered by light interactions rather than solely electrical bias at the base. They offer high gain and low cost, making them ubiquitous in 2026 consumer electronics. Figure 1: Phototransistor SymbolFunctionally, phototransistors share similarities with photoresistors (LDRs), but with a key distinction: phototransistors generate current and voltage through the photovoltaic effect and amplification, whereas LDRs only change resistance.Transistors with the base terminal exposed are chemically doped to maximize light sensitivity. Photons striking the depletion layer generate electron-hole pairs, activating the transistor just as a base current would in a standard BJT. Silicon-based photosensors typically respond to visible and near-infrared radiation (approx. 400nm to 1100nm). Ⅳ How are Phototransistors Constructed?The phototransistor's structure is specifically optimized for photo-applications by maximizing the area of the base-collector junction. While ordinary bipolar transistors exhibit some photosensitivity, phototransistors feature significantly larger base and collector areas to capture maximum light flux.Figure 2: Construction of a PhototransistorⅤ Semiconductor Material EvolutionHistorical phototransistors utilized a homo-junction structure, fabricated entirely from germanium or silicon. In contrast, modern 2026 phototransistors often employ type III-V semiconductor materials, such as gallium arsenide (GaAs), to target specific wavelengths and increase efficiency.Key structural variations include:NPN Topology: The most popular configuration due to the higher mobility of electrons compared to holes.Heterostructures: Utilizing different materials on either side of the PN junction to enhance conversion efficiency.Mesa Structure: A common physical layout for optimized light absorption.Schottky Junctions: Occasionally used for the collector to improve switching speeds.To ensure optimal sensitivity, the emitter contact is frequently offset, preventing it from blocking light from reaching the active region. Ⅵ How Does a Phototransistor Work?A phototransistor operates by using light to control the flow of current, effectively replacing the base current of a standard transistor with photon energy.Biasing: The collector is biased positively relative to the emitter (in NPN), creating a reverse-biased Base-Collector (B-C) junction.Injection: Light strikes the B-C junction, generating electron-hole pairs.Amplification: The movement of these carriers constitutes a base current, which the transistor amplifies by its gain factor (hFE).Typically, the physical base terminal is left unconnected (floating), as the device is controlled entirely by incident light. Ⅶ Key Electrical CharacteristicsSince phototransistors are essentially Bipolar NPN Transistors with an exposed junction, their V-I characteristics resemble a standard BJT family of curves, but with Light Intensity (mW/cm²) replacing Base Current (IB).Dark Current: When no light is present, a minuscule leakage current flows from collector to emitter. In high-precision applications, minimizing this Dark Current is crucial.Light Current: As light intensity increases, the base current rises, triggering the amplification process. Figure 3: Reverse Bias Configuration The collector current characteristics curve below demonstrates the linear relationship between light intensity and output current in the active region.Figure 4: Collector Current vs. Irradiance Ⅷ Selection Criteria & PropertiesWhen selecting a component for 2026 designs, engineers must evaluate specific properties to ensure the device matches the optical environment.Critical Datasheet Properties:Peak Wavelength: The specific color of light (e.g., 850nm IR vs. 560nm Visible) the device is most sensitive to.Linearity: How accurately the output follows the input light intensity.Sensitivity: The ratio of output current to incident light power.Response Time: The rise and fall time, which determines the maximum data rate (typically slower than photodiodes).Acceptance Angle: The field of view from which the sensor can detect light. Ⅸ Common Types: BJT vs. FETPhototransistors are primarily categorized by their internal transistor architecture:BJT Phototransistor: The standard type. In darkness, it leaks only ~100 nA. Under illumination, it can conduct up to 50mA. This high current handling capability distinguishes it from photodiodes.Photo-FET (Field Effect Transistor): Utilizes light to generate a gate voltage that controls the drain-source current. Photo-FETs offer extremely high input impedance and are more sensitive to weak light signals, though they are less common in general switching applications. Ⅹ Practical Circuit Examples (2026 Applications)The primary goal of phototransistor circuits is to generate a usable output voltage from light-induced current. Unlike photodiodes which often require Transimpedance Amplifiers (TIA), phototransistors have built-in gain, allowing for simpler circuit designs.Common Configurations:Common-Emitter (Inverting): Output voltage drops as light increases.Common-Collector (Non-Inverting): Output voltage rises as light increases.Figure 5: Basic Amplifier Configurations 10.1 Step-by-Step Circuit Implementations 1. Light Operated Relay (Automatic Day Switch)Mechanism: When light strikes phototransistor Q1, it conducts, supplying base current to the driver transistor Q2. Q2 then activates the mechanical relay, turning on the connected load. 2. Darkness Operated Relay (Night Light)Mechanism: By inverting the logic, the relay activates only when light is absent. In darkness, the phototransistor turns off (high resistance), allowing the bias resistor to trigger Q2. 3. Light Interruption Alarm (Security System)Mechanism: This circuit functions as a tripwire. Under normal conditions (laser/light hitting sensor), the phototransistor pulls the SCR gate LOW (off). When the beam is broken by an intruder, the gate voltage rises, latching the SCR and sounding the alarm until manually reset. Ⅺ Datasheet Specifications to WatchTo ensure system reliability, consult the following parameters in manufacturer datasheets:Collector Current (IC): Maximum current the device can handle (typically 1mA - 50mA).Dark Current (ID): Leakage current in total darkness (lower is better for precision).Peak Wavelength (λp): The wavelength of maximum sensitivity.VCE(sat): Collector-Emitter saturation voltage.Rise/Fall Time (tr/tf): Critical for optical data transmission applications.Power Dissipation (Ptot): Thermal limits of the package. ⅻ Pros and Cons AnalysisSelecting the right optical sensor requires balancing sensitivity, speed, and cost.AdvantagesDisadvantagesHigh Gain: Produces higher current output than photodiodes, reducing the need for external amplifiers.Limited Voltage: Cannot withstand high voltages compared to Thyristors or Triacs.Cost-Effective: Inexpensive to manufacture and integrate into ICs.Slower Speed: Slower response time (lower bandwidth) compared to PIN photodiodes.Simplicity: Can drive small relays or logic gates directly in simple circuits.Temperature Sensitivity: Dark current increases significantly with temperature fluctuations. XIII Modern Applications in 2026Due to their versatility, phototransistors are integral to many modern technologies:Optocouplers (Optoisolators): Protecting low-voltage logic circuits from high-voltage spikes in power supplies.Optical Encoders: Used in robotics and motors to detect position and speed.Object Detection: Proximity sensors in smartphones and automated manufacturing lines.Safety Systems: Smoke detectors and light curtain barriers for industrial machinery.Remote Control Receivers: IR detection for consumer electronics (though often integrated with demodulators). XIV Comparison: Photodiode vs. PhototransistorWhile both detect light, their use cases differ based on speed and sensitivity needs.FeaturePhotodiodePhototransistorOutputLow Current (µA)High Current (mA) - AmplifiedResponse SpeedVery Fast (Nanoseconds)Moderate (Microseconds)ApplicationsFiber Optics, High-Speed DataRemote Controls, Light Switches, EncodersNoiseLow NoiseHigher Noise levels XV Frequently Asked Questions1. What type of device is a phototransistor?A phototransistor is a bipolar semiconductor device. It functions as a transistor where the base current is generated by incident photons striking the exposed semiconductor junction, rather than an electrical connection.2. What is the main difference between a standard transistor and a phototransistor?Physically, the primary difference is the packaging. A phototransistor has a transparent lens or window to allow light to reach the junction, and it often lacks an external base pin. Electrically, it is controlled by light intensity rather than input current.3. Is a phototransistor considered a sensor?Yes, it is a discrete photosensor. It detects the presence and intensity of light and converts it into a measurable electrical signal.4. How do you test if a phototransistor is working?You can test it using a multimeter or a simple circuit:Connect the phototransistor in series with a resistor and LED to a power source (checking polarity).Expose the sensor to light; the LED should brighten.Cover the sensor; the LED should dim or turn off.5. Which is better: Photodiode or Phototransistor?Neither is universally "better"; it depends on the application. For high-speed data (like fiber optics), a photodiode is superior. For switching and sensing without extra amplifiers, a phototransistor is more efficient due to its internal gain.{ "@context": "https://schema.org", "@graph": [ { "@type": "Article", "headline": "Phototransistors: The Ultimate 2026 Guide", "datePublished": "2021-12-02", "dateModified": "2026-01-07", "description": "A comprehensive guide to phototransistors, covering construction, working principles, circuit diagrams, and 2026 applications.", "image": "https://www.kynix.com/editor_u/image/20211202/2021120216390176.jpg", "author": { "@type": "Organization", "name": "Kynix Electronics" } }, { "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "What type of device is a phototransistor?", "acceptedAnswer": { "@type": "Answer", "text": "A phototransistor is a bipolar semiconductor device where the base current is generated by incident photons striking the exposed junction." } }, { "@type": "Question", "name": "What is the difference between a transistor and a phototransistor?", "acceptedAnswer": { "@type": "Answer", "text": "The main difference is that a phototransistor has an exposed optical window and is controlled by light intensity, whereas a standard transistor is controlled by electrical current at the base pin." } }, { "@type": "Question", "name": "Is a phototransistor a sensor?", "acceptedAnswer": { "@type": "Answer", "text": "Yes, a phototransistor is a discrete photosensor that converts light intensity into an electrical signal." } }, { "@type": "Question", "name": "Which is better: Photodiode or Phototransistor?", "acceptedAnswer": { "@type": "Answer", "text": "Photodiodes are better for high-speed data applications, while phototransistors are better for switching and sensing applications requiring higher sensitivity and gain." } } ] }, { "@type": "HowTo", "name": "How to Build a Simple Light Interruption Alarm", "step": [ { "@type": "HowToStep", "name": "Setup the Phototransistor", "text": "Connect the phototransistor to a pull-down resistor to create a voltage divider." }, { "@type": "HowToStep", "name": "Connect the SCR", "text": "Connect the output of the phototransistor junction to the Gate of an SCR (Silicon Controlled Rectifier)." }, { "@type": "HowToStep", "name": "Align the Light Source", "text": "Point a laser or light beam directly at the phototransistor. This keeps the SCR gate low (Off)." }, { "@type": "HowToStep", "name": "Trigger the Alarm", "text": "Interrupt the light beam. The phototransistor turns off, voltage spikes at the SCR gate, latching the alarm on." } ] } ]}

IntroductionIn the lighting industry, people often have a misunderstanding about dimming LED lights. And the reality is that the application of LED light source dimming technology in engineering is often unsatisfactory. Why is this the case? Is the LED light source dimming technology immature, or the technology is difficult to master? So this article analyzes the LED dimmer to help readers to fully understand and master it.Dimming all kinds of LEDs?CatalogIntroductionⅠ Dimming LED Lights1.1 What is Dimming?1.2 LED Dimming Circuit Example1.3 LED Dimming Using SCRⅡ Dimming LED Using PWM2.1 LED Dimming Current2.2 LED PWM Dimmer2.3 LED PWM Dimming Advantages2.4 LED PWM Dimming Problems2.5 DALI PWM Dimmer IntroductionⅢ Main LED Dimmers ComparisonsⅠ Dimming LED Lights1.1 What is Dimming?LED dimmer switch is an electrical device that changes the luminous flux of the light source in the lighting device and adjusts the illuminance level. The purpose of the dimmer is to adjust the different brightness of the light. By reducing or increasing the rms voltage, the light output of different intensities produced by the average power lamp is promoted. Although variable voltage devices can be used for various purposes, this regulation is aimed at controlling lighting. Regarding the LED dimmer switch, we must first understand the volt-ampere characteristics of the LED. That is, the characteristics of the current flowing through the LED PN junction with voltage. Generally, the reverse characteristic curve changes steeply. When the voltage exceeds a certain threshold, the current will rise exponentially, thereby breaking down the LED PN junction. The forward voltage of the LED is also determined by its forward current. It can be seen from the figure that the change of the forward current will cause the corresponding change of the forward voltage, to be precise, the decrease of the forward current will also cause the decrease of the forward voltage. Therefore, when the current is lowered, the voltage of the LED will also decrease, which will change the relationship between the power supply voltage and the load voltage.Figure 1. Diode Volt-Ampere Characteristics CurveTherefore, from the volt-ampere characteristics of the LED, we can know that the dimming of the light source cannot be achieved simply by reducing the input voltage or input current of the LED. In addition, the waveform of the sine wave of the LED is different from the waveform of the incandescent lamp, so it cannot simply change its conduction angle to achieve the purpose of dimming.LED dimming methods can be divided into analog dimming and digital dimming. Analog dimming is to achieve dimming by changing the current in the LED loop. The power supply voltage remains unchanged, and the current in the loop is changed by changing the resistance value to achieve the effect of changing the brightness of the LED. Many analog dimming is an extension of this method. Its advantage is that the current can be continuous, but the range of adjustable current is often limited by hardware, and there are few adjustment gears. This method is not ideal for high-precision lighting equipment.Digital dimming, also known as PWM (Pulse Width Modulation) dimming, uses PWM waves to turn on and off the LED to change the on-time of the forward current to achieve the effect of brightness adjustment. This method is based on the fact that the human eye is not sensitive enough to the brightness flicker. If the frequency of brightness and darkness exceeds 100Hz, the average brightness is seen by the human eye, not the LED flickering. PWM adjusts the brightness by adjusting the ratio of light and dark time. In a PWM cycle, because the perceived brightness of human eyes to flicker is a cumulative process, that is, the brighter time accounts for the greater the proportion of the entire cycle. The longer the time, the brighter the human eye feels.1.2 LED Dimming Circuit ExampleFor example, in an LED lamp with an input of 24V, 8 1W high-power LEDs are connected in series. When the forward current is 350mA, the forward voltage of each LED is 3.3V, then 8 pieces in series is 26.4V, so a constant current source greater than 24V should be used. However, in order to dimming, the current is reduced to 100mA. At this time, the forward voltage is only 2.8V, and 8 pieces are connected in series to 22.4V. The load voltage becomes lower than the input voltage, so that a constant current source larger than 24V cannot work, and finally the LED will flicker.In this case, you may choose a step-down (wide voltage) constant current source, such as a 10V-30V constant current source for dimming. However, if this type is adjusted to a low forward voltage, the LED load current will also become very low. So the step-down ratio is very large, beyond the normal working range of constant current source, which will make LED unable to work and cause flicker. In addition, LED works at low brightness for a long time, which will reduce its efficiency and increase the temperature rise. Because the efficiency of the step-down constant current source is related to the voltage ratio, the larger the voltage drop ratio, the lower the efficiency. And greater power loss on the chip will damage the life of the constant current source and the LED light source.1.3 LED Dimming Using SCROrdinary incandescent lamps and halogen lamps usually use thyristors for dimming. Because they are pure resistance devices, and do not require the input voltage to be a sine wave. Their current waveform is always the same as the voltage waveform, no matter how the voltage waveform deviates from the sine wave, changing the effective value of the input voltage will dim the LED light .However, the adjustment of LED light source by thyristor dimming will cause unexpected problems, that is, the LC filter at the input will cause the thyristor to oscillate. This oscillation is indifferent to the incandescent lamp, human eyes can't see it at all because of thermal inertia. However, this dimming method will cause the driving power of LED produce audio noise and flicker. It will also destroy the waveform of the sine wave, thereby reducing its power factor value (usually lower than 0.5), which greatly reduces the system efficiency of the LED. Moreover, the thyristor dimming waveform increases the harmonic coefficient, and the non-sinusoidal waveform will cause serious electromagnetic interference on the line to pollute the power grid.Ⅱ Dimming LED Using PWM2.1 LED Dimming CurrentHere, you may ask: Lower voltage or current or thyristor dimming methods are not suitable for LED light source dimming, so what is the most suitable method?Is it an analog (0-10V) dimming method? May be not. Analog dimming faces a severe challenge, which is the output current accuracy. Almost every LED driver needs some kind of series resistance to distinguish the current, and the tolerance, offset and delay in the analog (0-10V) dimming drive cause a relatively fixed error, which will reduce the accuracy of the output current, and the final output current cannot be specified, controlled or guaranteed. Therefore, to ensure the dimming effect of the LED light source, one of the important rules is to reduce the output current error and improve the current accuracy in a closed loop system.2.2 LED PWM DimmerThe PWM dimming method can solve the above problems very well. Because diode characteristics, LED can realize fast switching, and its allowable switching speed can be as high as microseconds or more. Therefore, as long as the power supply is changed to a pulse constant current source, the brightness can be changed by PWM. This PWM dimming. This method is like a sluice that opens and closes in microseconds or more. The switching frequency of it is so fast that humans can’t recognize the state of its opening with the naked eye. As a result, people can only identify the speed of its switching frequency by the amount of water downstream. In addition, because the sluice changes the duty cycle of the output water flow (effective water flow), it does not change the instantaneous water pressure and flow rate, so the opening and closing action of the sluice gate will not affect the hydropower generation. The amount of water flowing down and power generation are just changed. Therefore, the PWM dimming method does not change the instantaneous voltage and current of the input LED PN junction, but changes the duty cycle of the output current to change LED brightness.2.3 LED PWM Dimming Advantages1) There will not be any LED chromatogram shift, because the LED always works between the full amplitude current and 0.2) It has a very high dimming accuracy, because the pulse waveform can be controlled to a high precision.3) Even if the light is dimmed in a wide range, there will be no flicker. Because it will not change the working conditions of the constant current source (boost ratio or step-down ratio), problems such as overheating are less to occur.4) It can be combined with digital (DALI/DSI/DMX 512) control technology for control, because the digital control signal can easily be transformed into a PWM signal.2.4 LED PWM Dimming Problems1) Because the LED is in a fast switching state, if the working frequency is very low, the human eye will feel flicker. In order to make full use of the residual visual phenomenon of the human eyes, its operating frequency should be higher than 100Hz, preferably 200Hz.2) Eliminate the howling caused by dimming. Although the human eye can't detect it above 200Hz, it is within the range of human hearing until 20kHz. At this time, it is possible to hear the slightest voice. There are two ways to solve this problem: One is to increase the switching frequency above 20kHz, out of the range of human hearing, another is to find out the sound-producing device and deal with it.At present, some manufacturers have solved the above problems well. A good LED light source dimming technology needs a good LED control signal technology to match and cooperate in order to become an effective, stable and reliable system. For example, the LED PWM dimming method has the advantage that the digital control signal can easily be converted into a PWM signal. At the same time, in the digital control signal of lighting, DALI (Digital Addressable Lighting Interface) has the unparalleled superiority of other lighting digital control methods, and it is also the mainstream of the current digital control application in the lighting industry. Therefore, the matching of PWM dimming mode and DALI takes into account their respective advantages, where PWM dimming technology solves the final dimming problem of LED light sources, and DALI solves the control, feedback and networking of each LED light.Figure 2. LED PWM Dimming Circuit2.5 DALI PWM Dimmer IntroductionThe biggest feature of DALI technology is that each lamp has an independent address. Through the DALI system software, a single lamp or any lamp set can be accurately dimmed and switched, regardless of whether the lamps are on strong current loop or not. That is to say, the lighting control has nothing to do with the strong current circuit. The DALI system software can independently address single or multiple lamps on the same strong current circuit or different circuits, to achieve individual control and arbitrary grouping set. This concept brings great flexibility to lighting control, which can meet different LED lighting requirements. Even after installation, they can still modify the control requirements at will, without having to do anything to the wiring.The following are the application advantages of PWM dimming method combined with DALI.1) The design is simple and easy to implement.In the design, as long as they are connected to each other through the digital signal interface, they are connected in parallel to the 2-core control line. All design process can be programmed by computer software during installation and debugging, which not only saves design costs, but also improve working efficiency.2) Simple and economical installationThe DALI control line has no special requirements for the wire and no polarity requirements during installation. It only requires the main power line to be separated from the control line. The control line does not need to be shielded. When the current on the control line is 250mA and the line is 300 meters long, the drop does not exceed 2V. The control line and the power line can be parallel, no need to bury the line separately. The compact design of the control components does not require a special control cabinet, so installation is simple and economical.3) Simple and convenient operationThe PWM LED driver with DALI control can automatically handle filament preheating, ignition, dimming, switching, fault detection and other functions. The user interface is very friendly. Users can operate and control without deep understanding, such as sending a change. According to the command of the scene, each relevant LED driver calculates the dimming rate according to the difference between the current brightness and the required installation brightness to achieve that all the LED light sources are synchronized to the required scene brightness.4) Accurate and reliable controlDALI is a digital signal, which is different from an analog signal. The signal of 1010 can realize disturbance-free control, and will not distort the control signal due to long-distance voltage drop. Therefore, even if the DALI digital signal control line and the strong wire are in the same line and tube, it will not be disturbed. The DALI signal is two-way transmission, which not only transmits control commands forward, but also feeds back the information of the LED driver's status, fault information, switch, and actual brightness value to the system.5) Wide range of applicationsNowadays, DALI interface is not only used for fluorescent lamp ballast dimming, various electronic transformers for halogen lamps, electronic ballasts for gas discharge lamps. DALI technology also employed in wide range of LED light control makes it more and more widely. Ⅲ Main LED Dimmers Comparisons1) SCR DimmingFigure 3. SCR Dimming Circuit Diagram✅Advantages: It has the advantages of high adjustment accuracy, small size, light weight, easy remote control, etc., which occupies a leading position in the market.❎Disadvantages: The front-cut LED dimmer is prone to generate noise, so it is not recommended for high-demand occasions. The minimum load will vary depending on the LED dimmer and light source. It is necessary to consider derating to adapt to the spike caused by the driver. The typical derating percentage should be 25%-30% of the maximum rated load of the dimmer circuit. 2) CMOS DimmingFigure 4. CMOS Dimming Circuit Diagram✅Advantages: There is no minimum load requirement, so that better performance can be achieved on a single LED lighting device or a very small load.❎Disadvantages: High cost, complicated dimming circuits, lack of high-power products, and poor stability. 3) 0-10V DimmingFigure 5. 0-10V Dimming Circuit Diagram✅Advantages: Simple application, good compatibility, high precision, better dimming effect than phase-cut dimming.❎Disadvantages: Need to add additional control lines and controllers. The dimming effect is related to the wire diameter, cable material, power current, and power supply quantity of 0-10V dimming. 4) DALI DimmingFigure 6. DALI Dimming Circuit Diagram✅Advantages: Accurate and smooth dimming, two-way communication, and strong anti-interference ability, mainly used in single lamp control.❎Disadvantages: Like 0-10V products, additional control circuits and controllers need to be added. 5) DMX512 DimmingFigure 7. DMX512 Dimming Circuit Diagram✅Advantages: Powerful control functions bring rich lighting effects to architectural lighting, night lighting, studios and variety shows.❎Disadvantages: Special wiring layout and types are required, and certain programming is required to set the basic colors and scenes, which is more costly for later maintenance. The ideal transmission distance of DMX signal is less than 200 meters. And meanwhile, in actual use, the signal is greatly interfered by the outside world. 6) SLC and Ready2mains DimmingFigure 8. LED Dimming via Ready2mains✅Advantages: The digital dimming signal is transmitted through the AC wire, without additional signal wires and wiring. Digital signal transmission has good anti-interference performance and excellent dimming effect.❎Disadvantages: At present, there are relatively few products using this type of digital dimming technology, so there are relatively few compatible products. Frequently Asked Questions about LED Dimmer1. What are LED dimmers?An LED dimmer is the term for a device that performs a dimming control operation within such an LED lighting device. LEDs react instantaneously to alterations in power input, making solid state lighting especially suitable for dimming scenarios. 2. Why do my LED dimmer lights flicker?LED bulb flickering can be traced in almost every instance to a non-compatible dimmer switch in the lighting circuit. ... LED bulbs don't have glowing filaments. When the dimmer switch goes off and on many times per second, the LED bulb becomes a flickering strobe light. 3. Do you need a special dimmer for LED lights?Use an LED Dimmer switchA standard dimmer switch cannot be used with an LED light as you will never be able to dim the LED light either completely or not very well. LED lights need their own special electronic dimmer switch to have a fully functioning and dimming light. 4. How do LED dimmer switches work?In the case of PWM, dimmable LEDs work by creating a dimming effect. Unlike traditional lighting such as incandescent, dimmable LED bulbs don't rely on voltage to dictate their level of brightness. Instead, they essentially rely on a cycle of being on and off. 5. What is the best dimmer switch for LED lights?Best Overall: Lutron Toggler Single-Pole/3-Way Light Dimmer.Best Budget: GE Slide Dimmer Rocker Wall Switch, Single Pole.Best Smart: Kasa Smart Dimmer Switch HS220.Best for Bedrooms: Lutron Maestro LED+ Dimmer Switch, Single-Pole or Multi-Location.Best for LED: Lutron Diva LED+ Dimmer Switch, Single-Pole or 3-Way.

I IntroductionSummary: A photoresistor, or light-dependent resistor (LDR), is a passive electronic component that decreases in resistance as light intensity increases. Driven by the expansion of IoT and smart home automation, the global photoresistor market is projected to reach $553.75 million by 2025. This guide covers LDR working principles, circuit diagrams, types, and step-by-step Arduino integration.Photoresistor or light-dependent resistor (abbreviated as LDR) or photoconductor is a special resistor made of semiconductor materials such as cadmium sulfide or cadmium selenide. Its working principle is based on the internal photoelectric effect. The stronger the light, the lower the resistance value. With the increase of the light intensity, the resistance value decreases rapidly, and the bright resistance value can be as small as 1KΩ or less. The photoresistor is very sensitive to light, and it shows a high resistance state when there is no light, and the dark resistance can generally reach 1.5MΩ.This article includes an overview of the basic information of the photoresistor and two Arduino tutorials for the photoresistor. The content is very comprehensive and detailed. You can choose the part you want to read or read the full text. We hope this article is helpful to you!II What is a Photoresistor?2.1 What is the Definition of a Photoresistor?A photoresistor (also known as a light-dependent resistor, LDR, or photo-conductive cell) is a passive electronic component that decreases its electrical resistance as the luminosity on its sensitive surface increases.2.2 What is the Symbol for a Photoresistor?The standard schematic symbols for a photoresistor are generally represented by the designators "RL", "RG", or "R", often accompanied by a resistor icon enclosed in a circle with incoming arrows indicating light. The following figure shows the schematic symbols of the photoresistor.Figure1. Photoresistor SymbolRecommended Reading: To learn more about Resistor Symbol.2.3 What is the Composition of a Photoresistor?(1) The structure of the photoresistorA photoresistor is primarily composed of a photosensitive semiconductor layer, a glass substrate or moisture-proof film, and comb-shaped ohmic electrodes.Figure2. The Structure of PhotoresistorMaterials for manufacturing photoresistorsThe materials used for manufacturing photoresistors are primarily semiconductors such as metal sulfides, selenides, and tellurides. Usually, coating, spraying, sintering and other methods are used to make a very thin photoresistor and comb-shaped ohmic electrode on the insulating substrate, and then the lead is taken out and encapsulated in a sealed housing with a light-transmitting mirror to prevent moisture from affecting its sensitivity.III How Does the Photoresistor Work?3.1 What is the Working Principle of Photoresistors?How does a photoresistor workThe working principle of a photoresistor is based entirely on the internal photoelectric effect, where incident light energy excites electrons into the conduction band, thereby lowering the component's electrical resistance.A voltage is applied to the metal electrodes at both ends of the photoresistor, and a current flows through it. When irradiated with light of a certain wavelength, the current will increase with the increase of light intensity, thereby achieving photoelectric conversion. After the incident light disappears, the electron-hole pairs generated by the photon excitation will recombine, and the resistance of the photoresistor will return to its original value.The photoresistor has no polarity and is purely a resistive device. It can be used with either DC voltage or AC voltage. The conductivity of a semiconductor depends on the number of carriers in the semiconductor conduction band. Why is the value of the photoresistor related to the wavelength of the incident light?Simply put, it is the effect of transitions between energy levels. Photons at different wavelengths have different energies, and an electron can only absorb one photon. After an electron absorbs a photon, whether it can be converted from non-conductive to conductive electrons depends on the photon’s Energy, and the number of electrons that can conduct electricity determines the resistance of the photoresistor. Therefore, the light wavelength also affects the resistance of the photoresistor.Recommended Reading: See more about light sensor, wavelength, spectrum and photometric physical quantity.3.2 What is the Internal Photoelectric Effect?The internal photoelectric effect is a phenomenon where the absorption of photons causes a change in the electrical conductivity of a semiconductor material. This differs from the external photoelectric effect, which involves the complete escape of electrons from the material's surface.The internal photoelectric effect can be divided into two main categories:Photoconductive effect: The change in electrical resistance due to light exposure.Photovoltaic effect: The generation of a photo-induced electromotive force (voltage) across a P-N junction. PhotoconductivityThe photoconductive effect is one of two internal photoelectric effects. The internal photoelectric effect refers to the phenomenon that the electrical conductivity of a semiconductor exposed to light changes or a photo-induced electromotive force is generated. Among them, the phenomenon that the conductivity of the semiconductor changes due to light is called the photoconductivity effect.Figure3. Energy Level of AtomPhotovoltaic EffectThe photovoltaic effect occurs when a P-type and N-type semiconductor are combined, creating a P-N junction. The process unfolds as follows:Electrons in the N-type semiconductor and holes in the P-type semiconductor diffuse, forming a depletion region near the interface.When light irradiates the P-N junction, photons with sufficient energy generate minority carriers (electron-hole pairs).Under the action of the internal electric field, excited electrons flow to the N-type region, and holes flow to the P-type region.This accumulation generates an additional electromotive force (voltage) at both ends of the P-N junction.If connected to an external circuit, current flows from the P region to the N region, producing usable electrical power.Figure4. Photovoltaic EffectIV How Do You Wire a Photoresistor Application Circuit?Schematic circuit for conventional applicationsFigure5. Schematic CircuitModule parameters:Working voltage: DC3.3-5VPhotoresistor Model: 5516Module pins: 3-pin or 4-pin (an additional analog output AO for 4-pin)Common circuit diagram （3）Photoresistor application circuit diagramThe following figure is a schematic diagram of the application of the photoresistor in the light control switch. The photoresistor is connected in series with the resistor R1. When there is no light, that is, the voltage across R1 does not reach the turn-on voltage of the Q1 transistor. Once exposed to light, the resistance of the photoresistor drops rapidly. The voltage across R1 rises and the transistor turns on, which causes the transistor Q2 in the subsequent stage to turn on, and finally, the switch K opens and the bulb works.Figure6. Common Photoresistor Application Circuit Diagram(4) Photoresistor dimming circuitThe following figure is a typical light-controlled dimming circuit. Its working principle is: when the surrounding light becomes weak, the resistance of the photoresistor RG increases, which increases the partial voltage added to the capacitor C, which in turn makes the thyristor's conduction angle is increased to achieve the purpose of increasing the voltage across the lamp. Conversely, if the surrounding light becomes brighter, the resistance of RG decreases, resulting in a smaller conduction angle of the thyristor, and the voltage across the lamp decreases at the same time, dimming the light, thereby controlling the illuminance of the lamp.Figure7. Photoresistor Dimming CircuitNote: The rectifier bridge in the above circuit must be a DC pulsating voltage, and it cannot be converted into a smooth DC voltage by capacitor filtering, otherwise the circuit will not work properly. The reason is that the DC pulsating voltage can not only provide the basic conditions for the zero-crossing shutdown of the thyristor, but also enable the charging of the capacitor C to start from zero every half cycle, and accurately complete the synchronous phase-shift triggering of the thyristor.V What Are the Types of Photoresistors?5.1 Classification by MaterialsBased on material composition, photoresistors are classified into intrinsic (pure semiconductor) and extrinsic (doped semiconductor) types. Polycrystalline and single crystal photoresistors can also be divided into cadmium sulfide (CdS), cadmium selenide (CdSe), lead sulfide (PbS), lead selenide (PbSe), indium antimonide (InSb) photoresistors, etc. 5.2 Classification by Spectral CharacteristicsSpectral TypeCommon MaterialsPrimary Applications (2026)Ultraviolet (UV)Cadmium sulfide, Cadmium selenideUV detection, environmental monitoringInfrared (IR)Lead sulfide, Lead telluride, Indium antimonideAstronomical detection, non-contact measurement, IR communicationVisible LightSelenium, Silicon, Germanium, Zinc sulfideIoT smart lighting, automatic street lights, exposure devices(1) Ultraviolet photoresistor: sensitive to ultraviolet rays, including cadmium sulfide, cadmium selenide photoresistors, etc., used to detect ultraviolet rays.(2) Infrared photoresistors: mainly lead sulfide, lead telluride, and lead selenide. Photoresistors such as indium antimonide are widely used in missile guidance, astronomical detection, non-contact measurement, human disease detection, infrared spectroscopy, infrared communication and other national defense, scientific research, and industrial and agricultural production.(3) Visible light photoresistors: including selenium, cadmium sulfide, cadmium selenide, cadmium telluride, gallium arsenide, silicon, germanium, zinc sulfide photoresistors, etc. Mainly used in various photoelectric control systems, which account for a significant portion of the projected $553.75 million global photoresistor market in 2025. Applications include IoT smart lighting, automatic turning on and off of navigation lights, street lights and other lighting systems, automatic water supply and automatic water stop devices, automatic protection devices on machinery and "position detectors" Thickness detectors for thin parts, automatic exposure devices for cameras, photoelectric counters, smoke alarms, photoelectric tracking systems, etc.Figure8. Light Dependent ResistorVI The Main Parameters and Basic Characteristics of the Photoresistor6.1 What Are the Main Parameters of a Photoresistor?The main parameters of a photoresistor define its operational limits, sensitivity, and response time in various lighting conditions.1) Bright resistance (kΩ): refers to the resistance value of the photoresistor when exposed to light.2) Dark resistance (MΩ): refers to the resistance value of the photoresistor when there is no light exposure (dark environment).3) Maximum working voltage (V): refers to the highest voltage the photoresistor is allowed to withstand under the rated power.4) Bright current: refers to the current that the photoresistor passes when it is irradiated by light under the specified applied voltage.5) Dark current (mA): refers to the current that the photoresistor passes under the specified applied voltage when there is no light.6) Time constant (s): refers to the time required for the photoresistor to start from the light jump to stabilize 63% of the bright current.7) Resistance temperature coefficient: refers to the relative change of the resistance value of the photoresistor when the ambient temperature changes by 1°C.8) Sensitivity: refers to the relative change of the resistance value of the photoresistor with and without light irradiation.Figure9. LDR6.2 Basic Characteristics(1) Dark resistance and bright resistanceThe stable resistance value measured by the photoresistor under room temperature and total darkness is called dark resistance. The current flowing at this time is called dark current. For example, MG41-21 type photoresistor dark resistance is greater than or equal to 0.1M.The stable resistance value measured by the photoresistor at room temperature and under certain lighting conditions is called bright resistance. The current flowing at this time is called the bright current. The bright resistance of MG41-21 type photoresistor is less than or equal to 1k.    The difference between bright current and dark current is called photocurrent.    Obviously, the larger the dark resistance of the photoresistor, the better, and the smaller the bright resistance, the better, that is, the dark current should be small and the bright current should be large, so the sensitivity of the photoresistor is high.Figure10. Bright Current and Dark Current(2) Volt-ampere characteristicsUnder a certain illuminance, the relationship between the voltage applied across the photoresistor and the current flowing through the photoresistor is called the volt-ampere characteristic. The volt-ampere characteristic of the photoresistor is approximately a straight line, and there is no saturation phenomenon. Due to the limitation of power dissipation, the voltage across the photoresistor cannot exceed the maximum operating voltage during use. The dotted line in the figure is the allowable power consumption curve, from which the normal operating voltage of the photoresistor can be determined. (3) Photoelectric characteristics    The relationship between the photocurrent of the photoresistor and the illuminance is called the photoelectric characteristic. The photoelectric characteristics of the photoresistor are nonlinear. Therefore, it is not suitable as a detection element, which is one of the shortcomings of the photoresistor. In automatic control, it is often used as a switching photoelectric sensor.Figure11. Characteristics of the Photoelectric Effect(4) Spectral characteristicsFor incident light of different wavelengths, the relative sensitivity of the photoresistor is different. The spectral characteristics of various materials are shown in Figure 2.6.4. It can be seen from the figure that the peak value of cadmium sulfide is in the visible light region, and the peak value of lead sulfide is in the infrared region. Therefore, when selecting the photoresistor, the types of components and light sources should be considered in order to obtain satisfactory results. (5) Frequency characteristicsWhen the photoresistor is exposed to pulsed light, the photocurrent will reach a steady-state value after a period of time. When the light suddenly disappears, the photocurrent will not be zero immediately. This shows that the photoresistor has time-delay characteristics. Because different materials have different time delay characteristics of photoresistors, their frequency characteristics are also different. Figure 2.6.5 shows the relationship between the relative sensitivity Kr and the light intensity change frequency f. It can be seen that the use frequency of lead sulfide is much higher than that of thallium sulfide. However, most photoresistors have large time delays, so they cannot be used in situations where fast response is required. This is a defect of photoresistors. (6) Temperature characteristicsLike other semiconductor devices, the photoresistor is greatly affected by temperature. When the temperature increases, its dark resistance will decrease. Changes in temperature also have a great influence on spectral characteristics. Figure 2.6.6 is the spectral temperature characteristic curve of the lead sulfide photoresistor. It can be seen from the figure that its peak value moves to the short wavelength direction as the temperature rises. Therefore, in order to improve the sensitivity, or in order to receive far-infrared light, cooling measures are taken.Figure12. Temperature CharacteristicsSpectral Temperature Characteristics of Lead Sulfide Photoresistor A commonly used photoresistor is a cadmium sulfide photoresistor, which is made of semiconductor material. The resistance of the photoresistor changes with the intensity of the incident light (visible light). Under dark conditions, its resistance (dark resistance) can reach 1~10MΩ; under strong light conditions (100LX), its resistance (Bright resistance) Only a few hundred to thousands of ohms. The sensitivity of the photoresistor to light (the spectral characteristics) is very close to the human eye's response to visible light (0.4~0.76) μm. As long as the human eye can sense the light, it will cause its resistance to change. Therefore, when designing the light control circuit, the incandescent bulb (small electric bead) light or natural light is used as the control light source, which greatly simplifies the design.Figure13. Photoresistor Characteristic CurveThe corresponding resistance change of the photoresistor with the intensity of the incident light is not linear, so it cannot be used for the linear conversion of the photoelectricity. This is where the user should pay attention. Beginners can purchase a photoresistor (MG45 type), at night a 60~100W incandescent lamp, use a multimeter to directly measure the resistance of the photoresistor. When measuring, the photoresistor should be aimed at the light of the incandescent lamp, and then gradually distance from the lamp (from near to far), observe the change of the resistance value indicated by the multimeter, and the special characteristics of the photoresistor can be visually verified.Commonly used photoresistor models are sealed MG41, MG42, MG43 and unsealed MG45 (cheap price). Their rated power is below 200mW.VII How to Use a Photoresistor with Arduino?7.1 LED Control with Photoresistor and ArduinoLED Control with LDR (Photoresistor) and Arduino7.2 How to Measure Light Intensity Using a Photoresistor (Arduino)In the data collection of modern smart home systems, the measurement of light intensity is highly necessary. For example, indoor IoT lighting can be automatically adjusted according to the intensity of the light to provide users with the most comfortable environment. The tutorial here will use a photoresistor to cooperate with Arduino to complete the light data collection.(1) MaterialsArduino UNO development boardBreadboardPhotoresistor1K-10K resistance(2)Wiring method Figure14. Wiring MethodThe resistance of photosensitive resistors is very high in the condition of no light. The stronger the light, the smaller the resistance. By measuring the voltage variation on both sides of the photosensitive resistance, the variation of the photosensitive resistance can be known and the light intensity can be obtained. In the connection diagram, we find that a partial voltage resistor is connected in series for the photosensitive resistor.Figure15. CircuitIn the above figure, RL is a photoresistor, R1 is a series resistor, Vout=RLR1+RL∗Vin, in the dark, the resistance of RL will be very large, so Vout is also very large, close to 5V. Once the light is irradiated, the value of RL will decrease rapidly, so Vout will decrease accordingly. It can be seen from the above formula that R1 should not be too small, preferably around 1k~10k, otherwise the ratio will not change significantly. (3) CodeThe code part is very simple, just read the analog value of the interface connected to the photoresistor.1 light = analogRead(0);Open the serial monitor of Arduino, illuminate the photoresistor with the flashlight of the mobile phone, and observe the result:2 Serial.println("lignt :");3 Serial.println(light);7.3 Use Experiment of Arduino Photoresistor(1) MaterialsArduino UNO x1Photoresistor x1resistance 10K, 4.7K, 1K x several (or need one, but you can test the difference between different resistance values and data)(2)Wiring method Figure16. Wiring Method(3)Program#define AD5 A5 //Define analog port A5#define LED 13 //Define digital port 13 int Intensity = 0;//Illuminance value void setup() //Program initialization{   pinMode(LED, OUTPUT);//Set LED to output mode   Serial.begin(9600);//Set baud rate 9600} void loop() // Program body loop{   Intensity = analogRead(AD5); //Read the value of analog port AD5 and save it in the Intensity variable   Serial.print("Intensity = "); //Serial output "Intensity = "   Serial.println(Intensity); //The serial port outputs the value of the Intensity variable and wraps   delay(500); //Delay 500ms}(4) Power on, view serial dataTest Results:Figure17. Test ResultsThe above data is the change of the value with the flashlight and no light.(5) SummaryThe positive and negative poles are reversed and the values are reversed. The larger the resistance value, the larger the change range. Using 5V, the range is larger than 3.3V.Recommended Reading: Arduino&mBlock light sensorVIII How to Use Multimeter to Detect the Quality of Photoresistor?Measure the dark resistance: Use a black piece of paper to cover the light-transmitting window of the photoresistor. At this time, the pointer of the multimeter remains basically unchanged, and the resistance value is close to infinity. The larger the value, the better the performance of the photoresistor. If this value is very small or close to zero, it means that the photoresistor has been burnt through and damaged and can no longer be used.Measure the bright resistance value: Point a light source to the light-transmitting window of the photoresistor. At this time, the pointer of the multimeter should have a large amplitude swing, and the resistance value is significantly reduced. The smaller the value, the better the photoresistor performance. If this value is large or even infinite, it indicates that the internal open circuit of the photoresistor is damaged and can no longer be used.Test intermittent light response: Align the light-transmitting window of the photoresistor with the incident light, and use a small piece of black paper to shake the upper part of the light-shielding window of the photoresistor to make it receive light intermittently. At this time, the pointer of the multimeter should swing left and right with the black paper. If the pointer of the multimeter always stops at a certain position and does not swing with the shaking of the paper, it means that the photosensitive material of the photoresistor has been damaged.IX A Quiz about the PhotoresistorPhotoresistors, potentiometers, and thermistors are all ________.A. OutputsB. Digital inputsC. Analog inputsD. ThroughputsAnswer: CFrequently Asked QuestionsWhat is the difference between a photoresistor and a photodiode?A photoresistor is a passive component that changes resistance based on light intensity, making it slower but easier to use. A photodiode is an active semiconductor with a P-N junction that converts light into current, offering much faster response times for high-speed applications.Is a photoresistor an analog or digital component?A photoresistor is fundamentally an analog component. Its resistance changes continuously in response to varying light levels. However, when paired with a microcontroller like an Arduino and a voltage divider, its analog signal can be easily converted into digital data.What are the main types of photoresistors?Photoresistors are primarily categorized into intrinsic and extrinsic types. Intrinsic photoresistors use pure semiconductors like silicon, while extrinsic types use doped materials to detect longer wavelengths, such as infrared light, making them ideal for specialized sensors.How is a photoresistor used in smart home circuits?In modern IoT and smart home systems, photoresistors act as ambient light sensors. They automatically trigger actions like turning on outdoor security lights, adjusting indoor smart bulb brightness, or activating motorized blinds when sunlight reaches a specific threshold.{ "@context": "https://schema.org", "@graph":[ { "@type": "Article", "headline": "Photoresistor Basics: Working Principle, Types, and Arduino Tutorial", "datePublished": "2020-06-19T00:00:00Z", "dateModified": "2026-03-14T15:57:00+08:00", "author": { "@type": "Organization", "name": "ApogeeWeb" }, "publisher": { "@type": "Organization", "name": "ApogeeWeb" } }, { "@type": "FAQPage", "mainEntity":[ { "@type": "Question", "name": "What is the difference between a photoresistor and a photodiode?", "acceptedAnswer": { "@type": "Answer", "text": "A photoresistor is a passive component that changes resistance based on light intensity, making it slower but easier to use. A photodiode is an active semiconductor with a P-N junction that converts light into current, offering much faster response times for high-speed applications." } }, { "@type": "Question", "name": "Is a photoresistor an analog or digital component?", "acceptedAnswer": { "@type": "Answer", "text": "A photoresistor is fundamentally an analog component. Its resistance changes continuously in response to varying light levels. However, when paired with a microcontroller like an Arduino and a voltage divider, its analog signal can be easily converted into digital data." } }, { "@type": "Question", "name": "What are the main types of photoresistors?", "acceptedAnswer": { "@type": "Answer", "text": "Photoresistors are primarily categorized into intrinsic and extrinsic types. Intrinsic photoresistors use pure semiconductors like silicon, while extrinsic types use doped materials to detect longer wavelengths, such as infrared light, making them ideal for specialized sensors." } }, { "@type": "Question", "name": "How is a photoresistor used in smart home circuits?", "acceptedAnswer": { "@type": "Answer", "text": "In modern IoT and smart home systems, photoresistors act as ambient light sensors. They automatically trigger actions like turning on outdoor security lights, adjusting indoor smart bulb brightness, or activating motorized blinds when sunlight reaches a specific threshold." } } ] }, { "@type": "HowTo", "name": "How to Use Multimeter to Detect the Quality of Photoresistor", "step":[ { "@type": "HowToStep", "name": "Measure the dark resistance", "text": "Use a black piece of paper to cover the light-transmitting window of the photoresistor. At this time, the pointer of the multimeter remains basically unchanged, and the resistance value is close to infinity. The larger the value, the better the performance of the photoresistor. If this value is very small or close to zero, it means that the photoresistor has been burnt through and damaged and can no longer be used." }, { "@type": "HowToStep", "name": "Measure the bright resistance value", "text": "Point a light source to the light-transmitting window of the photoresistor. At this time, the pointer of the multimeter should have a large amplitude swing, and the resistance value is significantly reduced. The smaller the value, the better the photoresistor performance. If this value is large or even infinite, it indicates that the internal open circuit of the photoresistor is damaged and can no longer be used." }, { "@type": "HowToStep", "name": "Test intermittent light response", "text": "Align the light-transmitting window of the photoresistor with the incident light, and use a small piece of black paper to shake the upper part of the light-shielding window of the photoresistor to make it receive light intermittently. At this time, the pointer of the multimeter should swing left and right with the black paper. If the pointer of the multimeter always stops at a certain position and does not swing with the shaking of the paper, it means that the photosensitive material of the photoresistor has been damaged." } ] } ]}

I IntroductionThe light-emitting diode is a commonly used light-emitting device, which emits energy through the recombination of electrons and holes. It is widely used in the field of lighting. Light-emitting diodes can efficiently convert electrical energy into light energy. Light-emitting diodes have a wide range of uses in modern society, such as lighting, flat panel displays, and medical devices.Light Emitting Diode (LED) Working PrincipleThis kind of electronic component appeared as early as 1962. In the early days, it could only emit low brightness red light. Later, other versions of monochromatic light were developed. The light that can be emitted today has spread to visible light, infrared light, and ultraviolet light. Initially,  the light-emitting diodes were used as indicator lights, display panels, etc. With the continuous progress of technology, light-emitting diodes have been widely used in displays and lighting.CatalogI IntroductionII Parameters of Light-emitting Diode2.1 Significance of Limit Parameters2.2 Significance of Electrical ParametersIII Working Principle of Light-emitting DiodeIV Types of Light-emitting DiodeV Materials of a Light-emitting Diode5.1 Wafer5.2 Bracket5.3 Silver glue 5.4 Gold wire 5.5 Epoxy resinVI Applications of Light-emitting Diode6.1 Display Screen and Communication Signal Display6.2 Automotive Industry6.3 LCD Backlight6.4 LED Lighting6.5 Other ApplicationsVII Trends of LED Lighting TechnologyII Parameters of Light-emitting Diode2.1 Significance of Limit Parameters(1) Allowable power consumption Pm: the maximum value of the product of the forward DC voltage applied to both ends of the LED and the current flowing through it. If this value is exceeded, the LED becomes hot and damaged.(2) Maximum forward DC current IFm: the maximum forward DC current allowed to be added. Exceeding this value can damage the diode.(3) Maximum reverse voltage VRm: the maximum reverse voltage allowed to be applied. Above this value, the light-emitting diode may be damaged by the breakdown.(4) Working environment topm: the ambient temperature range where the LED can work normally. Below or above this temperature range, the light-emitting diode will not work properly and the efficiency is greatly reduced.2.2 Significance of Electrical Parameters(1) Spectral distribution and peak wavelength: the light emitted by a certain light-emitting diode is not a single wavelength, and its wavelength is generally shown in Figure.Figure 1. Spectral Distribution and Peak WavelengthIt can be seen from the figure that the light intensity of a certain wavelength λ0 in the light emitted by the light-emitting tube is the largest, and this wavelength is the peak wavelength.(2) Luminous intensity IV: The luminous intensity of the light-emitting diode usually refers to the luminous intensity in the direction of the normal. When the radiation intensity in this direction is (1/683) W / sr, it emits 1 candela (symbol cd). Since the general LED has a low luminous intensity, the luminous intensity is usually measured in candela (mcd).(3) Spectral half-width Δλ: It represents the spectral purity of the light-emitting tube. It refers to the interval between the two wavelengths corresponding to the 1/2 peak light intensity in Figure 3.(4) Half value angle θ1 / 2 and viewing angle: θ1 / 2 refers to the angle between the direction in which the luminous intensity value is half of the axial intensity value and the luminous axis (normal direction).Two times the half-value angle is the viewing angle (or half-power angle).Figure 2. Angle Distribution of Luminous Intensity of the LEDFigure above shows the angular distribution of the luminous intensity of two different types of LEDs. The coordinates of the perpendicular (normal) AO are the relative luminous intensity (ie, the ratio of the luminous intensity to the maximum luminous intensity). Obviously, the relative luminous intensity in the normal direction is 1. The larger the angle away from the normal direction, the smaller the relative luminous intensity. From this graph, the half-value angle or viewing angle value can be obtained.(5) Forward working current If: It refers to the forward current value when the light-emitting diode is normally emitting light. In actual use, the IF should be selected below 0.6·IFm.(6) Forward working voltage VF: The working voltage given in the parameter table is obtained under a given forward current. Generally measured at IF = 20mA. The forward working voltage VF of the light-emitting diode is 1.4 ~ 3V. When the outside temperature increases, VF will decrease.(7) V-I characteristics: The relationship between the voltage and current of the light-emitting diode can be represented in the figure below.Figure 3. The Relationship between the Voltage and Current of the LEDWhen the forward voltage is less than a certain value (called a threshold), the current is extremely small and does not emit light. When the voltage exceeds a certain value, the forward current increases rapidly with the voltage and emits light. From the V-I curve, parameters such as the forward voltage, reverse current, and reverse voltage of the light-emitting tube can be obtained. The forward leakage current IR of the LED tube is less than 10μA.III Working Principle of Light-emitting DiodeThe core part of the light-emitting diode is a wafer composed of a P-type semiconductor and an N-type semiconductor. There is a transition layer between the P-type semiconductor and the N-type semiconductor, called a PN junction. In the PN junction of some semiconductor materials, the injected minority carriers and majority carriers will release excess energy. The energy is in the form of light, thereby directly converting electrical energy into light energy. The reverse voltage is added to the PN junction. Minority carriers are difficult to inject, so they do not emit light. This kind of diode is called a light-emitting diode, commonly known as LED. When it is in the forward working state (that is, the forward voltage is applied to both ends), and when the current flows from the anode to the cathode of the LED, the semiconductor crystal emits light of different colors from ultraviolet to infrared. The intensity of the light is related to the current.The principle of light-emitting diode needs to be analyzed from the following three situations:When no voltage is applied across the diode, the electrons in the N-type material will move along the PN junction between the layers. The electrons fill the holes in the P-type material and form a depletion region. In the depletion region, the semiconductor material returns to its original insulation state. That is, all holes are filled, so there is neither free electrons nor space for electrons to move in the depletion region, and the charge cannot flow.Figure 4. No Voltage is Applied Across the DiodeWhen a forward voltage is applied to the light-emitting diode, the holes injected from the P region to the N region. And the electrons injected from the N region into the P region within a few microns near the PN junction. They recombine with electrons in the N region and holes in the P region respectively. Therefore, they produce spontaneously emitted fluorescence. Different semiconductor materials have different energy states for electrons and holes. The more energy released, the shorter the wavelength of the emitted light. Diodes that emit red, green, or yellow light are commonly used.Figure 5. Apply a Forward Voltage to the LEDWhen a reverse voltage is applied to the light-emitting diode, the P-type terminal is connected to the negative electrode of the circuit, and the N-type terminal is connected to the positive electrode. And the current will not flow. Negatively charged electrons in N-type materials will be attracted to the positive electrode. Positively charged holes in P-type materials will be attracted to the negative electrode. Since holes and electrons move in the wrong direction. No current will flow through the PN junction, and the depletion region will also expand.Figure 6. Apply a Reverse Voltage to the LED LED materialColorAlGaAs GaAsP AlGaInP GaP:ZnOred and infrared InGaN/GaN GaP AlGaInP AlGaPgreenGaAsPAlGaInP AlGaInP GaPhigh brightness orange red, orange, yellow, greenGaAsPred, orange, yellowGaP ZnSe InGaN SiCred, yellow, greenGaNgreen, emerald green, blueInGaNnear ultraviolet, blue green, blueSiCblueSiblueAl2O3blueZnSeblueCultravioletAlN AlGaNUV with wavelengths far to nearTable: Inorganic Semiconductor Materials Used in Light-emitting Diodes and the Colors They EmitIV Types of Light-emitting DiodeThere are various types of light-emitting diodes according to different aspects. According to the materials used, there are gallium phosphide (GaP) light-emitting diodes, phosphorous gallium arsenide (GaAsP) light-emitting diodes, gallium arsenide (GaAs) light-emitting diodes, phosphorous indium gallium arsenide (GaAsInP) light-emitting diodes and gallium arsenide aluminide (GaAlAs) light-emitting diodes.According to its packaging structure and packaging form, there are metal packaging, ceramic packaging, plastic packaging, resin packaging, and leadless surface packaging. It can also be divided into additive color scattering package (D), colorless scattering package (W), colored transparent packaging (C), and colorless transparent packaging (T).Figure 7. Kinds of Light-emitting DiodeAccording to its package shape, it can be divided into circular, square, rectangular, triangular, and combined shapes. The figure shows the shape of several light-emitting diodes.Plastic light-emitting diodes are divided into red, amber, yellow, orange, light blue, green, black, white, transparent, and colorless according to the color of the tube body. The outer diameter of the round light-emitting diode is from ￠ 2 to ￠ 20mm. According to the light-emitting color of the light-emitting diodes, it can also be colored light and infrared light. Colored lights include red light, yellow light, orange light, green light, and so on. In addition, light-emitting diodes can be divided into ordinary monochrome light-emitting diodes, high-brightness light-emitting diodes, ultra-high-brightness light-emitting diodes, color-changing light-emitting diodes, flashing light-emitting diodes, voltage-controlled light-emitting diodes, infrared light-emitting diodes, and negative resistance light-emitting diodes.V Materials of a Light-emitting DiodeWafer, bracket, silver glue, gold wire, and epoxy resin are the five LED raw materials of light-emitting diode5.1 WaferThe structure of the wafer: it consists of a gold pad, P-pole, N-pole, PN junction, and a back gold layer (the double-pad wafer has no back gold layer). The wafer is composed of P-layer semiconductor elements and N-layer semiconductor elements. They are rearranged and combined by electron movement. It is this change that enables the wafer to be in a relatively stable state. When the positive electrode is applied to the wafer with a certain voltage, the holes in the positive P region will continue to swim toward the N region. And the electrons in the N region will move to the P region relative to the holes. While the electrons and holes move relatively, the electron holes pair with each other, exciting photons and generating light energy.The main classification of wafer: surface-emitting type: most of the light is emitted from the surface of the wafer. Five-sided light-emitting type: there is more light emitted on the surface and side.5.2 BracketThe structure of the bracket is 1 layer of iron, 1 layer of copper (good conductivity, fast heat dissipation), 1 layer of nickel (anti-oxidation), 1 layer of silver (good reflectivity, easy to solder wire)5.3 Silver glue Take H20E as an example. Silver glue is also called white glue, milky white. The role of silver glue is to conduct and bond materials (baking temperature: 100°C / 1.5H). Storage conditions: Silver glue manufacturers generally store silver glue at -40°C, and application units generally at -5°C. Single-agent is 25°C / 1 year (dry, ventilated place), mixed agent 25°C / 72 hours. Baking conditions: 150°C / 1.5H. Stirring conditions: Mix for 15 minutes in one direction.5.4 Gold wire Take φ1.0mil as an example. The gold wires used for LEDs are φ1.0mil and φ1.2mil. The material of the gold wire is generally 99.9% of the gold content of the gold wire for LED. The purpose of the gold wire: with its characteristics such as high gold content, soft, easy to deform, good conductivity and good heat dissipation, a closed circuit is formed between the wafer and the bracket. (Conversion relationship: 1 mil = 0.0254mm, 1 in = 25.4mm)5.5 Epoxy Resin Ttake EP400 as an example. Composition: A and B two parts: Glue A: it is the main agent, which consists of epoxy resin + defoamer + heat resistance agent + thinner. Agent B: it is a curing agent, consisting of acid, mold release agent, and accelerator.VI Applications of Light-emitting Diode6.1 Display Screen and Communication Signal DisplayLED lamp has the characteristics of shock resistance, fast light response, power-saving, and long life, etc. It is widely used in various indoor and outdoor displays. It is divided into full-color, three-color, and monochrome displays that are developed and produced by more than 100 units nationwide. Traffic lights mainly use ultra-high-brightness red, green, and yellow LEDs. Because LED lights are energy-saving and reliable, the traffic lights are gradually being replaced throughout the country and the speed of promotion is fast.Figure 8. Traffic Lights6.2 Automotive IndustryAutomotive lamps include dashboards, audio indicators, backlights for switches, reading lights and external brake lights, tail lights, sidelights, and headlights. Incandescent lamps for automobiles are not resistant to shock that require frequent replacement. Due to the fast response speed of the LED, the driver can be reminded of the brakes early to reduce the rear-end accident. In developed countries, the central rear high-position brake light made of LED has become a standard part of the car. The LED car tail light model launched by the American HP company in 1996 Groups can be combined into various car taillights at will. In addition, the light sources in the car dashboard and other various lighting parts can be used as ultra-high brightness light-emitting lamps. In recent years, an annual output value of 1 billion yuan will be formed, and within 5 years, an annual output value of 3 billion yuan will be formed.Figure 9. Automotive Headlight6.3 LCD BacklightLED backlights are most noticeable with high-efficiency side-emitting backlights. As an LCD backlight application, LEDs have the characteristics of long life, high luminous efficiency, no interference, and high-cost performance. They have been widely used in electronic watches, mobile phones, BP, computers, electronic calculators, and credit card machines. With the increasing miniaturization of portable electronic products, the LED backlight has more advantages.  The backlights manufacturing technology will be developed to thinner, low power consumption, and uniformity. LED is the key device of a mobile phone. An ordinary mobile phone needs about 10 LED devices, while a color screen and a mobile phone with camera function need to use about 20 LED devices. At present, the amount of mobile phone backlight is very large. 3.5 billion LED chips are used a year.6.4 LED Lighting  Early lighting products have low luminous efficiency. The light intensity can only reach a few to dozens of mcd, which is suitable for indoor occasions, such as home appliances, instrumentation, communication equipment, microcomputers, and toys. At present, the direct goal is to replace incandescent lamps and fluorescent lamps with LED light sources. This substitution trend has started to develop from local application fields. To save energy, Japan is planning to replace the incandescent light-emitting diode project (called "illuminate Japan"). The budget for the first five years is 5 billion yen. If LED replaces half of the incandescent and fluorescent lamps, the annual savings can be equivalent to the energy of 6 billion liters of crude oil. That is equivalent to the power generation of five 1.35 × 106kW nuclear power plants. It can reduce the production of carbon dioxide and other greenhouse gases and improve the living environment.6.5 Other ApplicationsFigure 10. LED Christmas LightsOther applications such as a kind of flash shoes popular with children, the built-in LED will flash when walking; the power indicator of electric toothbrushes; the popular LED Christmas lights. Due to the novel shape, rich colors, unbreakable and low-voltage safety Sexuality, LED Christmas light is generally welcomed by people. It is threatening and replacing the existing Christmas market of electric bulbs.VII Trends of LED Lighting Technology1. The mainstream light source of lighting will be converted to LED. At present, the luminous efficiency of high-power led commercial products has reached more than 150lm / W. The life span has reached more than 30,000 hours. The comprehensive performance of LEDs has exceeded other light sources. At the same time, in addition to large power, the price of LED lamps is close to lamps composed of other light sources. Therefore, LED already has certain advantages. At the same time, the light efficiency of LED laboratory products has reached more than 300lm / W. Through a reasonable heat dissipation design, the life span of more than 50,000 hours can be fully achieved. In principle, there is not much room for other light sources to improve light efficiency and life. Therefore, it can be expected that LED becoming the mainstream light source in the lighting market.2. The research of LED device technology will mainly focus on the improvement of green LED efficiency. The core device of semiconductor technology-LED, currently the red LED and the blue LED has high photoelectric efficiency, but the photoelectric efficiency of the green LED is very low. This limits the substantial application of LED spectral flexibility. Therefore, improving the light efficiency of green LEDs is the most important research topic of LED devices.3. Another study of LED technology will be the study of narrow-spectrum LED devices. The narrow spectral width of a single LED will help to truly achieve unlimited flexibility in assembling the LED spectrum. At the same time, one of the main applications of LEDs at present-LED displays, if the spectral width of monochromatic LEDs can be reduced, a larger color gamut space can be achieved.4. White LEDs for general lighting will gradually shift to RGB mode. The light sources used for general lighting are presented in the form of white light or near-white light. At present, the most comprehensive and cost-effective white LEDs on the market are also implemented by blue LEDs and YAG phosphors. However, the RGB method has higher light efficiency. It will enable the lamp to be dimmed, toned, and even adjusted the color rendering index. Therefore, with the improvement of green LED light efficiency, it is believed that the RGB method (further extended to 3 or more monochromatic LED mixed colors) will become the mainstream white LED mode.5. The characterization of the color rendering of the light source will be a long-term debate. The characterization in the form of the spectrum may be the ultimate result. The current parameter that characterizes the color rendering of the light source is the color rendering index. However, this is based on the limited spectral form of traditional light sources. The infinite flexibility of the LED spectrum will make this characterization problematic. It can be predicted that if the LED achieves true spectrum unlimited flexibility. Any single-parameter color rendering will actually be flawed, and the ultimate characterization method should be the spectrum itself.6. The application of light sources will include two basic aspects of visual applications and non-visual applications. The flexibility of LEDs in spectral assembly makes it possible to achieve various visual and non-visual optimized applications through spectral assemblies, such as agricultural lighting, medical lighting, LED Visible light communication, etc. But relatively speaking,  in the non-visual field, there are still many problems to be solved, including what kind of lighting conditions are optimized, the price of LED needs to be further reduced. The former is a scientific problem, while the latter is an industrialization problem.7. Lighting technology will be deeply integrated with information technology to create smart lighting. As a semiconductor device, LED is a good physical carrier of information technology because LED is easy to control plus the relevance of lamps and human life. Therefore, LED can be deeply integrated with information technology, and smart lighting will be born. This will be an important development direction for future LED lighting technology.8. The appearance of the lamps and lanterns will have great innovation potential. At present, most LED lamps and lanterns include LED bulbs, LED downlights, LED tubes, etc., all of which are designed to cater to people's consumption habits. Whether this is the best mechanical form of the lamp or not remains to be studied. At least, there is a lot of room for innovation in the future mechanical form of LED lamps.9. OLED will occupy an important position in the display field. Relative to LEDs that emit light similar to point light sources, OLEDs emit light in the form of surface light sources. Therefore, after LED occupies the vast majority of lighting applications in the future, OLED still has certain advantages in the display field.10. Natural lighting will be valued. In recent years, energy-saving lighting, health lighting, and ecological lighting have received great attention. The use of sunlight to achieve lighting naturally becomes the best choice. Therefore, with the advancement of technology, natural light lighting will receive more and more attention.Due to the great flexibility of LEDs in the three dimensions of scale, spectrum, and time, many innovative applications and concepts may be born in the future of LED development. This is the development trend of lighting based on artificial light sources. At the same time, as people continue to deepen the concept of green environmental protection, natural lighting will also get greater development. Frequently Asked Questions about Light-emitting Diode Tutorial1. What does light emitting diode mean?In the simplest terms, a light-emitting diode (LED) is a semiconductor device that emits light when an electric current is passed through it. Light is produced when the particles that carry the current (known as electrons and holes) combine together within the semiconductor material. 2. What is a light emitting diode used for?Light emitting diodes, commonly called LEDs, are real unsung heroes in the electronics world. They do many different jobs in all kinds of devices. They form numbers on digital clocks, transmit information from remote controls, light up watches and tell you when your appliances are turned on. 3. What type of light does LED emit?LED lighting differs from incandescent and fluorescent in several ways. When designed well, LED lighting is more efficient, versatile, and lasts longer. LEDs are “directional” light sources, which means they emit light in a specific direction, unlike incandescent and CFL, which emit light and heat in all directions. 4. Why are LED lights so bright?LED lights are so bright because they have a high lumen/watt score. ... This is an enormous difference between the levels of light you are getting from each bulb and because the LED bulb is so much higher there is no way that you would need to replace a 40W incandescent bulb with the equivalent Watt in a LED. 5. What is the difference between diode and LED?The most significant difference between the LED and diode is that the LED emits the light while the diode allows the current to flow only in one direction and opposes the flow in the opposite direction. 6. What is the basic principle of LED?Working Principle: A light-emitting diode is a two-lead semiconductor light source. It is a p–n junction diode that emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. 7. Do LED lights give off UVB?Some in the lighting business have stated that LEDs do not produce UV radiation. However studies have shown that standard LEDs do create a small amount of UV. That said, the amount of UV they actually emit is even less. This is due to the phosphors within an LED lamp that convert the Ultraviolet light to white light. 8. What are the two basic types of LEDs?The two basic types of LEDs are indicator-type LEDs and illuminator-type LEDs. Indicator-type LEDs are usually inexpensive, low-power LEDs suitable for use only as indicator lights in panel displays and electronic devices, or instrument illumination in cars and computers. 9. What is LED and its advantages?Safety is perhaps the most often overlooked advantage when it comes to LED lighting. The number one hazard when it comes to lighting is the emission of heat. LEDs emit almost no forward heat while traditional bulbs like incandescents convert more than 90% of the total energy used to power them directly into heat. 10. What is the O in OLED?Organic contrastOLED stands for organic light-emitting diode. Each pixel in an OLED display is made of a material that glows when you jab it with electricity.

I IntroductionThis article introduces the basics of low voltage transformer, including the definition of low voltage transformer, the principle of low voltage transformer, its installation method, malfunction, and how to repair a household low voltage transformer. A transformer is an electronic instrument that we can use everywhere in our lives. For example, we are inseparable from the mobile phone chargers. The internal components also have transformers. For example, the power supply in our computers is also composed of transformers. Therefore, all electronic products are indispensable for transformers. The transformers used in electronic components are all power transformers (included low voltage transformers). The power transformer is mainly used in electronic products to convert the power supply to the voltage required by the electronic circuit.CatalogⅠIntroductionⅡ Basics of low voltage transformer2.1 Definition of low voltage transformer2.2 Types of low voltage transformers2.3 How does low voltage transformer work?2.4 Design requirements of low voltage transformer2.5 Application environmentⅢ Differences between low&high voltage transformerⅣ How to Estimate the Loss of Low Voltage TransformerV Guide to What You May be Interested in5.1 How to Install Low Voltage Transformer for Household?5.2 How to Troubleshoot a Low-Voltage Transformer5.3 Repairing a household transformer5.4 Malfunction of factory low voltage transformerVI One Question Related to Low Voltage Transformer6.1 Question (Multiple choice questions)6.2 AnswerVII FAQII Basics of Low Voltage Transformer2.1 Definition of Low Voltage Transformer Transformers are important power equipment in our life, especially low-voltage transformer. Whether it is for large-scale power plants or home circuits, it is inseparable from the transformer. There are two kinds of transformers used in our life, one is the high-voltage transformer which used in the high-voltage or ultra-high-voltage circuit, the other is the low-voltage transformer which used in the family lighting circuit or small power circuit.The so-called low-voltage transformer refers to the transformer with low load voltage. As long as the load is lower than 600V, it can be called a low-voltage transformer. The low-voltage transformer is mainly composed of primary coil, secondary coil, and a magnet iron circuit. Low voltage transformers are commonly used for low voltage lighting, which typically only uses 12 or 24 volts. 2.2 Types of Low Voltage TransformersThere are two main types of low voltage transformers: electronic and magnetic.（1）Electronic Low Voltage TransformersElectronic transformers are much smaller, lighter, and less expensive than magnetic counterparts. But they only have about a 5-6 year lifespan. Also, electronic low voltage transformers are known for being noisy.Electronic Low Voltage TransformersAdvantagesDisadvantages▪ Smaller and lighter, easier to hide▪ Less expensive▪ Shorter life span▪ Noisy▪ Heat-sensitive（2）Magnetic Low Voltage TransformersThere are two types of magnetic transformers: stack laminated and toroidal.  Stack laminated transformers have a longer lifespan, about 15 to 20 years. But they only operate at about 80 to 85 percent efficiency, also are known for being noisy.Toroidal transformers are very quiet and more energy efficient. They can operate at about 90 to 95 percent efficiency. And they are long-lived, lasting 20 to 25 years.Magnetic Low Voltage TransformersAdvantagesDisadvantages▪ Long life span of over 15 years▪ Energy efficient▪ Quiet▪ Heavy, big, and difficult to hide▪ Expensive2.3 How Does Low Voltage Transformer Work?Electricity and magnetism are two kinds of energy that can mutually transform. Electricity can generate magnetism, and magnetism can also generate electricity. The low-voltage transformer uses this principle to adjust the voltage through the mutual conversion of electricity and magnetism.A low voltage transformer consists of two electrical coils of wire, one of which is called primary winding and the other is called secondary winding. The primary side of the transformer collects power and the secondary side provides power.Figure 1. Low Voltage Transformer StructureThe two coils intertwine together on a magnet iron circuit core, but without electrically in contact with each other. The magnetic core is made of soft magnetic material, which consists of laminations connected together to help reduce core loss. The core allows power to be transferred from one coil to another. When the primary winding is connected to the power supply, the generated magnetic field transfers the voltage to the secondary winding.Figure 2.  How Does Low Voltage Transformer Work?In summary, the primary winding transforms the electrical power into magnet field when connected to the input voltage supply while secondary winding transforms alternating magnetic field into electrical power of required output.2.4 Design Requirements of Low Voltage TransformerThe low-voltage transformer should be vacuum cast, molded resin encapsulated, 60Hz, Class F insulation, comply with the requirements of IEC726, and meet the requirements of capacity, voltage, phase number, and wiring shown. Each low-voltage transformer has separate primary and secondary windings, and there are two 2.5% normal voltage full-capacity taps above and below the rated voltage on the primary side. The low-voltage transformer should be installed on a base that can isolate, reduce vibration and noise, and the iron core and coil should be properly fixed to withstand the mechanical stress generated in the event of line failure and can withstand 16460 Lite 16460-6 V2. 0 2002/ 11/ 25 Vibration and impact during shipment. Unless otherwise specified, the impedance of low-voltage transformers shall be in accordance with IEC 726. The average noise level of the low-voltage transformer should not exceed the value specified in IEC 726. Each dry-type low-voltage transformer should have appropriate terminals to accommodate the required primary and secondary wiring connections. Low-voltage transformers can be reserved for cable entry from either side or bottom.2.5 Application Environment(1) Ambient air temperature - 5 ℃ to + 40 ℃, 24-houraverage value not more than + 35 ℃(2) The altitude of the installation site shall not exceed 2000m(3) The relative humidity of the atmosphere shall not exceed50% when the ambient air temperature is + 40 ℃(4) A place without violent shaking and impact vibrationIII Differences Between Low&High Voltage Transformer Low Voltage TransformerHigh Voltage Transformerwindingcontinuous windingInterleaved WindingscoolingOil-immersed cooling or air coolingOil-immersed coolingstructureoil tank structurebell jar type oil tankⅣ How to Estimate the Loss of Low Voltage TransformerTransformer loss include copper loss and iron loss. The loss of iron loss is also called no-load loss, and the loss of copper loss is also called load loss. The open circuit of the secondary winding of the transformer applies the no-load current of rated frequency and rated voltage to the primary side, and the active loss caused by the transformer core is called the no-load loss of the transformer. The loss figure can be obtained by the unit loss of the iron core silicon steel sheet multiply the quality of the silicon steel sheet. In general, its loss is very small. For example, the S9-100/10 distribution transformer has a no-load loss of 290W. The larger the transformer capacity, the smaller the no-load loss, generally between 0.3-0.15% of the rated capacity. However, the transformer works continuously for 24 hours, and this loss cannot be ignored. The load loss: The short-circuit of the coil on the secondary side apply the rated current at the rated frequency on the primary side. The transformer loss at this time is the loss of the transformer coil and the iron core. Let's take the S9 series transformer as an example and see its load loss value:The load loss of S9-100/10000 transformer is 1500W.The load loss of S9-1000/10000 transformer is 10300W.The load loss of a transformer is generally between 0.9-1.8%. The larger the transformer, the smaller the load loss.V Guide to What You Maybe Interested in 5.1 How to Install Low Voltage Transformer for Household? First, make sure you have an outlet available. Most family homes will have several outdoor power outlets installed. Second, think about the layout of the lighting. It is important to plan ahead when installing low voltage lighting so that you can avoid any potential problems, especially with the setup.Third, choose a transformer.①Magnetic or Electronic.②Make sure to buy a transformer that can handle the lighting load you need it to.Fourth, install the transformer. Transformers are installed simply by plugging them into your outdoor outlet.5.2 How to Troubleshoot a Low-Voltage Transformer(1) First, check whether there are obvious abnormalities by observing the appearance of the transformer: such as whether the coil lead is broken, whether the insulating material has scorch marks, whether the fastening screw of the iron core is loose, whether the silicon steel sheet is rusted, and whether the winding coil is exposed Wait. (2) Test a transformer with a digital multimeter, open all secondary windings, put the multimeter in the AC block (500mA, in series into the primary winding). When the plug of the primary winding is inserted into the 220V AC mains supply, the multimeter indicates the no-load current value. This value shall not be greater than 10% - 20% of the full load current of the transformer. Generally, the normal no-load current of the power transformer of common electronic equipment should be about 100mA. If too much is exceeded, the transformer has a short-circuit fault. Low Voltage Electronic Transformer Troubleshooting Guide5.3 Repairing a Transformer(1) Understand the reasons for the problem. Generally, a transformer has failed due to some fault in the electrical circuit.(2) Check the replacement transformer. If the short circuit is caused by component failure, the new transformer may still burn out. If you replace the transformer, examine it to make sure that the incident will not occur again.(3) Check the condition of the external fuse. If the transformer has an internal fuse, there may not be a fuse on the power line. On the contrary, the device must be protected by a fuse mounted on the power circuit. Check whether the fuse is intact and replace the faulty fuse.(4) Check the secondary power consumption. Sometimes, this kind of consumption is very high, which leads to equipment failure. If the transformer has multiple ratings and the multimeter shows the value "OL" during the measurement, it may be a short circuit in the secondary winding.5.4 Malfunction of Factory Low Voltage Transformer(1) Abnormal sound in transformerThe abnormal sound inside the transformer may be caused by the following reasons:①Heavy overload causes buzzing sound inside the transformer; ② Due to poor internal contact or breakdown point, the transformer occurs crackle sound③ Some parts of the connection shaft and the core of the transformer are loose, which causes the silicon steel sheet to vibrate④ When there is a grounding or short-circuit fault in the power grid, a large current flows through the winding, which will produce strong noise⑤ The iron core, the winding discharges to the shell, or the core ground wire is disconnected. All these can make the transformer discharge sound. (2) The oil level of the transformer is too high or too lowUnder normal circumstances, the changes in oil temperature can cause a change in oil level. As the oil temperature changes, the oil level also changes accordingly. However, under abnormal conditions, abnormal oil levels can also be caused by faults such as oil seepage and water seepage and other accidents. Second, the change in oil temperature is related to load conditions, ambient temperature and other conditions. When the change of oil level is inconsistent with these elements, it may be a false oil level. (3) Transformer oil quality has deteriorated or oil temperature has suddenly increasedIn working condition, the main function of transformer oil is cooling and insulation. When running overheated for a long time or if water enters the casing and absorbs moisture, the oil quality will deteriorate. Through the oil mark, we can found  that the oil color is abnormally deepened or blackened. Through sampling and analysis, it can be detected that the oil contains carbon particles and moisture, the acid value increases, the flashpoint decreases, and the insulation strength decreases. This situation can easily lead to serious accidents. A sudden rise in oil temperature when the transformer is operating normally is often related to the overheating inside the transformer. The iron core catches fire, the internal screws are loose, the cooling device is faulty, the transformer is heavily overloaded, all may cause the oil temperature to rise suddenly. (4) Transformer on fireWhen the transformer is out of order and it is not handled in time, it may catch fire. When the transformer is on fire, the insulating oil burns and turns into gas, which makes the oil tank burst. The burning insulating oil sprays out of the transformer, which will cause equipment damage and property loss. The short circuit inside or outside the transformer wire, severe overload, a lightning strike may cause the transformer to catch fire.VI One Question Related to Low Voltage Transformer6.1 Question (Multiple choice questions)The winding of wire around a core which is connected to a source of energy is called the ______ coil.primarysecondarytertiary6.2 AnswerA、B  VII FAQ1. What are low voltage transformers?A low voltage transformer is at the heart of every landscape lighting system. It converts 120-volt current to a low voltage current (between 12-15 VAC). ... Magnetic transformers use two coils to reduce the voltage from 120 volts down to 12 volts. 2. What low voltage transformer do I need?Transformers generally range from 150- to 900-watt capacity. Matching the size of the transformer to the lighting design is important for the efficient operation and function of the system. House current, 120 volts, is reduced by a transformer to 12 to 20 volts, the current needed to operate low-voltage landscaping lights. 3. What are low voltage transformers used for?Low Voltage Transformers Low voltage transformers are power transformers that are used to change the voltage capacity of a low-voltage electrical transmission line. Typically, electronic low voltage transformers convert 120 volts into 12 volts or 24 volts. 4. How do you test a low voltage transformer?• Identify the transformer's terminals, using its label as a guide. • Turn a multimeter to its VAC function. • Test the transformer's input voltage with the multimeter, using the transformer's label as a terminal guide. • Test the transformer's output voltage with the multimeter. 5. How long do low voltage transformers last?20 to 25 years.They operate at about 90 to 95 percent efficiency and can run for a very long time, anywhere from 20 to 25 years. They also are much quieter, so you can place them close to the fixtures, rather than having to run wires a long way from the transformer to the fixture itself. 6. Can I plug a low voltage transformer into an extension cord?One warning though to be observed is to never use an extension cord between the transformer and the electrical outlet. Always plug the transformer directly into the power outlet. As you can see, low voltage outdoor lighting is not all that hard to install or maintain. 7. Can you hardwire a low voltage transformer?To hardwire a low voltage transformer, the main power should be turned off at the breaker panel before making any electrical connections. ... The polarity of these wires is not important; either wire on the output side of the transformer may be connected to either wire of the low voltage circuit. 8. Do you need a transformer for low voltage lighting?When operating low voltage lights, you need a transformer to convert your standard line voltage (120V or 277V) into low voltage (12V or 24V). This allows your lights to function properly. If you connect low voltage lights directly to line power, the higher voltage would cause them to burn out immediately. 9. How do you tell if a transformer is going bad?Symptoms of power quality issues include vibration, excessive buzzing or humming and overheating. Technicians should occasionally check the power of transformers that supply nonlinear loads, such as variable frequency drives (VFDs) or switching power supplies. 10. Can you replace a transformer with a light fitting?They will have a transformer either in the ceiling or light fitting. Some LED bulbs, like the Philips Master LED range, have in-built circuitry that can deal with most (but not all) transformers, so you don't have to change them. In other cases, you need to replace the transformer with an LED driver.