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I IntroductionThe ballast has become an important additional device in the gas discharge light source circuit. Because most gas discharge lamps are made using arc discharge characteristics and have negative characteristics (also known as negative resistance characteristics) where the voltage decreases with increasing current, it is impossible to establish a stable operating point. In order to stabilize the discharge and limit the working current of the lamp, ballast must be installed in the gas discharge light source circuit. This article will introduce what is a ballast, how does the ballast work, its function, type, fault symptoms, and how to replace a broken ballast.What is a ballast?CatalogI IntroductionII What is a Ballast?III Types of Ballasts 3.1 Inductive Ballast(Magnetic Ballast) 3.2 Electrical Ballast 3.3 Resistance Ballast 3.4 Magnetic Leakage Ballast 3.5 Capacitive Ballast 3.6 LC BallastIV The Function of the BallastV How to Replace a Ballast? 5.1 How to Tell If the Lamp is Broken or the Ballast is Broken 5.2 Symptoms of Ballast Failure 5.3 Replacement ProcedureVI Several Common Terms for Ballasts 6.1 Ballast Loss 6.2 Ballast Factor 6.3 Ballast Efficacy Factor 6.4 Crest Factor 6.5 Power FactorVII One Quiz about the BallastVIII FAQII What is a Ballast?The ballast is a device that acts as a current limiter and generates an instantaneous high voltage on the fluorescent lamp. It is made by wrapping the enameled wire around an iron core made of silicon steel. Such a coil with an iron core, when instantaneously turned on / off and powered on, will generate a high voltage by self-induction, which is added to the electrodes (filament) at both ends of the fluorescent tube. This action is carried out alternately. When the starter (bubble jump) is closed, the filament of the lamp tube conducts heat through the current limit of the ballast; when the starter is open, the ballast will generate a high voltage on the filament at both ends of the lamp tube. The filament emits electrons to hit the fluorescent powder of the tube wall, and the starter repeatedly turns on and off a few times, thereby turning on the lamp. When the lamp emits light normally, the internal resistance becomes smaller, and the starter will always maintain an open-circuit state so that the current will work stably through the lamp and the ballast to make the lamp emit light normally.Figure1. BallastIII Types of Ballasts3.1 Inductive Ballast(Magnetic Ballast)3.1.1 DefinitionInductive ballast, also known as magnetic ballast, is an iron core inductance coil. The nature of the inductance is that when the current in the coil changes, the magnetic flux will change in the coil, which will generate an induced electromotive force. Thus hindering the current changes. 3.1.2 How Does the Inductive Ballast Work?When the switch is a closed circuit of 220V, 50Hz AC power, the electric current flows through the ballast to the starter, lamp filament, the filament heating (at the beginning of the starter is broken, due to a greater than 180V AC voltage, the starter has jumped the gas inside the bubble glow discharge, jump bimetallic strip is heated inside the bubble expansion deformation, two electrodes together, forming pathways to the filament heating).Figure2. The Circuit of Inductive Ballast When the two electrodes of the starter are close together because there is no arc discharge, the bimetallic sheet cools, and the two electrodes are disconnected. Due to the inductance of the inductive ballast, when the two electrodes are disconnected, the current in the circuit suddenly disappears. Therefore, the ballast generates a high pulse voltage, which is superimposed with the power supply voltage and is added to both ends of the lamp tube to ionize the inert gas in the lamp tube and cause arc discharge. (High pulse voltage-time is about 1ms 600V ~ 1500V, the exact voltage value depends on the type of lamp). During the normal lighting process, the self-inductance of the ballast serves to stabilize the current in the circuit. 3.2 Electrical Ballast3.2.1 DefinitionAn electrical ballast is a type of ballast, which refers to an electronic device that uses electronic technology to drive an electric light source to produce the required lighting. The electronic components convert the energy of the power grid to meet the voltage and current required by the matching lamps with AC or DC power.Figure3. Electrical Ballast 3.2.2 How Does the Electrical Ballast Work?The power frequency power supply becomes a DC power supply after passing through a radio frequency interference (RFI) filter, full-wave rectification, and passive (or active) power factor corrector (PPFC or APFC). Through the DC / AC converter, output high-frequency AC power of 20K-100KHZ, which is added to the LC series resonant circuit connected to the lamp to heat the filament, and at the same time, a resonant high voltage is generated on the capacitor and added to both ends of the lamp tube. However, the "discharge" of the lamp tube is turned into the "on" state and then enters the light-emitting state. At this time, the high-frequency inductance plays a role in limiting the increase of the current and ensuring that the lamp tube obtains the lamp voltage and lamp current required for normal operation.Figure4. How an Electrical Ballast Work 3.3 Resistance BallastIt regulates the lamp current by the voltage on the resistor proportional to the current. In the gas discharge light source circuit equipped with DC power supply, the application of resistance ballast is relatively simple in design and processing, but the power consumption is large and the efficiency is low. Resistance gas ballasts are also used in gas discharge light source circuits equipped with AC power sources. For example, in self-ballasted high-pressure mercury lamp circuits, tungsten wires are used as resistance ballasts. But generally speaking, the application of a resistor ballast in an AC circuit will affect the lamp current waveform, and make the luminous efficiency of the lamp decrease and the stability deteriorate, but it can improve the circuit power factor. 3.4 Magnetic Leakage BallastThe magnetic leakage ballast is a type of LC leading peak type circuit. The fundamental wave is mutated by auto-coupling boost and local magnetic saturation, and then it resonates with the working capacitor to obtain a higher open-circuit voltage and longer-lasting lamp operating current. It is a kind of high power factor lighting circuit, the line power factor reaches 0.90 ~ 0.97, which has its unique advantages for point HID light sources.Figure5. Magnetic Leakage Ballast 3.5 Capacitive BallastA capacitor is used as a ballast in a gas discharge light source circuit equipped with an AC power source. It cannot limit the instantaneous current of the lamp, only the total amount of charge that passes through the circuit in each half-cycle. In the low-frequency AC circuit, the lamp current waveform will be seriously distorted, forming a high pulse peak current (effective value is not large), which has a very harmful effect on the lamp electrode, resulting in a significant reduction in lamp life. Therefore, capacitors are rarely used as ballasts in low-frequency AC circuits. In higher frequency (20 ～ 100kHz) AC circuits, capacitors can be used as ballasts to obtain satisfactory results. The power consumption is small, the current waveform distortion is small, the volume is small, the weight is light, and there is no noise.Figure6. Circuit for Ballast-Ignitor-Capacitor-Lamp 3.6 LC BallastThere are the following two forms. (1) Ballast composed of inductor and capacitor connected in series. The designed capacitive reactance is usually about twice the inductive reactance, and the total impedance is capacitive. It belongs to the advanced ballast, that is, the phase of the lamp current leads to the phase of the power supply voltage. Compared with resistive ballast and inductive ballast, the power consumption is small, especially with good steady current characteristics, and the short-circuit characteristics when the lamp is started are also good. Combined with the use of hysteretic inductance ballast, it can greatly improve the power factor of the circuit. However, the repetitive ionization voltage provided every half cycle when the power supply voltage is commutated is low, and the repetitive ignition ability is poor.Figure7. Circuit of the LC Ballast for T5 28W Lamps (2) Ballast composed of magnetic leakage transformer and capacitor. Generally, it belongs to the advanced ballast. If the parameters are selected properly, the circuit power factor can be better improved. Its main performance is the same as the previous form of LC ballast. If a special leakage magnetic transformer structure is selected in the design to form an LC leading peak ballast, in addition to the above advantages, it can also greatly improve repeated ignition ability. This is an ideal ballast. The disadvantage is that the design and processing are more complicated. To better understand this part, you can see more details about LC circuit. IV The Function of the BallastLimit the Starting Current of the Lamp to A Suitable RangeStarting current refers to the current through the lamp within 30 seconds after the lamp is powered on or during the lamp preheating process. In general (especially in the state of lowest temperature), the starting current is much larger than the operating current of the lamp, so each lamp has a maximum starting current. If the starting current is too large, the service life of the lamp will be shortened; if the current is too small, the lamp cannot be preheated to the normal starting state or the process from glow discharge to arc discharge cannot be completed. The starting current provided by the ballast should not only start the lamp in a short time but also not affect the normal service life of the lamp. The Open Circuit Voltage Provided Is Sufficient for the Lamp to Start SmoothlyWhen the open-circuit peak voltage of the ballast is used as the starting voltage of the lamp, it must be sufficient to ionize the gas in the gas discharge lamp, that is, to generate a peak current that causes a glow-to-arc transition discharge between the electrodes, so that the lamp can start to work. High-pressure mercury lamps and metal halide lamps are more difficult to start at low temperatures, and the open-circuit peak voltage provided by the ballast must be sufficiently high.Figure8. How Electronic Ballast Functions Prevent the Lamp Power from Changing GreatlyAlthough the lamp has a certain range of voltage values during the design and delivery of the lamp, the voltage value of the lamp changes during actual use and throughout its life. This requires the matching ballast to adjust it within a certain range so that the lamp power does not change significantly. The ideal ballast should be such that the lamp power of the newly used lamp and the lamp near the end of its life are not too different. Working Current of Automatic Control LampStable impedance within a certain voltage range is the basic condition that the impedance ballast can control the working current of the lamp. The ballast uses the time change rate of the voltage proportional to the current to adjust the working current of the lamp. When the open-circuit voltage in a certain period causes the lamp operating current to increase, the inductive effect of the ballast will limit the rate of current increase; when the current starts to decrease, the inductive effect will prevent the rate of current decrease. V How to Replace a Ballast?5.1 How to Tell If the Lamp is Broken or the Ballast is Broken(1) The fluorescent lamp requires a ballast to meet the voltage required for the fluorescent lamp to start and work. If the lamp is broken, you can try another lamp to trouble the lamp cover. If it can be lit, the lamp is broken, if it is still not lit, the ballast is broken; (2) Using a universal meter to measure the disconnection of the lamp filament can also be judged: use a universal meter to measure the two ends of the fluorescent lamp separately. If the resistance is not zero, it means that the fluorescent lamp is broken, and the light can be shorted According to the method, if the inspection of the two components of the lamp tube and the light emitter is good, the ballast is broken.Fluorescent Light Troubleshooting and Repair: starter, bulb or ballast?5.2 Symptoms of Ballast Failure(1) The shell of the lamp or ballast appears black.(2) Use an electric pen to detect the ballast. There is no electricity at the incoming and outgoing ends.(3) Use an electric pen to detect that there is electricity at the incoming end, but no electricity at the outgoing end, which means that there is a disconnection inside the ballast.(4) If the shell of the ballast is charged with an electric pen, it means that the ballast has a leakage problem.(5) Use an electric pen to detect that there is electricity at the incoming and outgoing ends. The housing is not live, but the light is off. The light is still off when the trigger is replaced.(6) Use a multimeter with a resistance level of 200 to measure the resistance of the coil. The resistance is infinite.Figure9. Flurescent Ballast Tear Down5.3 Replacement Procedure(1) Open the lampshade: There are three clips around the lampshade that can be rotated. Use a screwdriver to turn the clip away to remove the lamp cover. Place the removed clip in a fixed place so that it can be reinstalled.(2) Observe the position of each component(3) Check whether the old lamp is broken. In general, a section with a longer ring lamp will appear gray. In this case, we should know that it is caused by the sublimation of a substance inside the lamp tube under a high-temperature environment.(4) Remove the lamp: After the lamp cover is opened, remove it, you can see there is a wire slot on the ring lamp. A wire extending from the lamp holder in the center is inserted into this slot. This wire is plug-in type, just pull it out! The ring tube inside is clamped and fixed by three bent metal pieces. This piece of metal is elastic and breaks apart with a screwdriver. You can remove the ring lamp. Pay attention to the wiring inside.(5) Replace the ballast: the ballast of the ring lamp, the two white wires are 220V power cords, there is no difference between positive and negative. The four small round holes on the box are the sockets for the lamp feet. Remove the chassis, disconnect the power cord, put the ballast down, and replace it with a new one.(6) Ring lamp installation: The steps are exactly the reverse when they are removed. Fix the new lamp, and fix the lamp with the three bent metal cards. Use a screwdriver to tighten. Then connect the wires. Stick it with tape and fix it. At the same time, clamp the wire slot on the ring lamp.(7) Install the lampshade: put back the three clips that were just removed. Fix the lampshade. Turn on the power. You can test whether the light is on. If it's on, it's a good replacement lamp. Precautions:(1) Be sure to cut off the main power switch before operation;(2) When removing the lamp cover, small parts such as cards and screws must be placed. In order to reinstall it finally.Figure10. Ballast KitsVI Several Common Terms for Ballasts6.1 Ballast LossThis value represents that the energy consumed by the electronic ballast itself is converted into heat energy instead of light energy. This value can be calculated by subtracting the power consumed by all lamp tubes from the total output power. Generally speaking, the traditional 40W dual-lamp ballast consumes about 22W, while the electronic ballast consumes about 7W. 6.2 Ballast FactorThis value can show the relative effect of the light output of the electronic ballast. The value is the percentage obtained by dividing the measured light output of the electronic ballast by the light output of the standard ballast light. Generally speaking, the higher the value, the better the light output effect. For electronic ballasts, it must not be less than 0.9, but there are also electronic ballasts designed to emphasize high output values and its light output ratio can be up to 1.18 to 1.28. 6.3 Ballast Efficacy FactorThis value can be obtained by dividing the light output ratio (Ballast Factor) by the ballast input power value (Input Power). In the US market, sellers usually use this value to measure and compare the pros and cons of the efficiency of various electronic ballasts. The higher the value, the better the efficiency of the electronic ballast.Figure11. Impedance Ballast6.4 Crest FactorIt is also called wave height rate. This value has a direct and critical impact on the life of the lamp tube. Most lamp tube manufacturers recommend that this value is preferably less than 1.7. Excessively high values can easily cause blackening of the lamp tube and shorten the service life of the lamp tube. The definition of the crest factor refers to the peak current divided by the average current when an electronic ballast is used to light a fluorescent tube. 6.5 Power FactorThis value can represent the efficiency value of the electronic ballast to convert the external input voltage and current into available power. The higher the power factor value, the better the company that supplies the power system (referred to as the power company). In order to encourage consumers to use electronic ballasts with high power factors, foreign power companies have adopted a subsidy policy, but consumers generally think that the higher the PF value, the more power they save. This is a wrong concept because the amount of power saved is not related to the PF value.Figure12. Inductive BallastVII One Quiz about the BallastQuestion: Which of the following ballasts are required to have thermal protection?A. The ballast of a fluorescent luminaire installed indoors, including a replacement ballast for this type of luminaireB. A simple reactance ballast in a fluorescent luminaire with straight tubular lampsC. A ballast in a fluorescent exit luminaireD. A ballast in a fluorescent luminaire used for egress lighting and energized only during a failure of the normal supplyE. All of the aboveAnswer: A  VIII FAQ1. What does a ballast do?In a fluorescent lighting system, the ballast regulates the current to the lamps and provides sufficient voltage to start the lamps. Without a ballast to limit its current, a fluorescent lamp connected directly to a high voltage power source would rapidly and uncontrollably increase its current draw. 2. Do you need a ballast with LED lights?LED technology does not require a ballast to regulate the amount of energy flowing to the lights. LEDs require less energy and can be sensitive to excess energy. A ballast bypass is a common procedure to remove the ballast from the existing fixture. 3. What is ballast and why is it important?Ballast is defined as any solid or liquid that is brought on board a ship to increase stability. Ballasting is essential if a ship is carrying a heavy load in one hold and a lighter load in another, or when the ship is empty or facing rough seas. 4. What happens when a ballast goes bad?If the ballast is bad, then the needle won't move. If you're using a digital multimeter, often the digital readout will possibly list a ‘1’ when it doesn't find a measurable resistance. 5. Is ballast and choke the same?A choke is an inductor designed to have a high reactance to a particular frequency when used in a signal-carrying circuit. An electrical ballast (sometimes called control gear) is a device intended to limit the amount of current flowing in an electric circuit. 6. How long should a ballast last?According to the Certified Ballast Manufacturers Association, the average magnetic ballast lasts about 75,000 hours or 12 to 15 years with normal use. The optimum economic life of a fluorescent lighting system with magnetic ballasts is usually about 15 years. 7. How do I know if my ballast is T8 or T12?If no markings are available, the size in diameter of the tube is the easiest way to determine the type you have installed. T8 tubes are 1-inch in diameter and T12 tubes are 1 1/2 -inch. 8. How often does a ballast need to be replaced?A typical ballast will generally last about 20 years, but cold environments and bad bulbs can decrease this lifespan significantly. You can get a new ballast at a hardware store or home center and install it in about 10 minutes. 9. Can you bypass a ballast on a fluorescent light?If the existing fluorescent tube fixture you want to replace has a non-shunted tombstone, you can proceed with the ballast bypass procedure. Nonetheless, if the existing fixture offers a shunted tombstone, you should replace it with a non-shunted variant. 10. What's in a light ballast?They're usually rectangular black boxes with wires coming out of one or both ends. Lighting ballasts for fluorescent light bulbs and HID lamps made before 1980 may contain polychlorinated biphenyls (PCBs). When the manufacture of PCBs was banned, existing equipment containing PCBs was allowed to remain in use. 

I IntroductionThe light sensor is developed based on the photoelectric effect principle of semiconductors. It can be used to detect the intensity of ambient light, and it can also be used to detect the difference in light between different colored surfaces. Users can make projects that interact with light with it, such as smart dimming lights, a laser communication system or something more awesome.Light Sensor Using Arduino and LDR | Arduino Light SensorCatalogI IntroductionII Definition  2.1 What is a Sensor?  2.2 Definition of the Light SensorIII Spectrum and Photometric Physical Quantity  3.1 Spectrum  3.2 Photometric Physical Quantities  3.3 MID Display's Perception of Backlight Brightness Under Different IlluminationIV How the Light Sensor WorksV Types and Characteristics of Light Sensors  5.1 Photodiode Type  5.2 Photoresistor TypeVI Applications of Light Sensors  6.1 Types of Light Sensors in Application  6.2 Typical Applications  6.3 Practical Application CasesVII The Circuit Diagram of a Light Sensor  7.1 Model Introduction  7.2 Appearance and Size  7.3 Application  7.4 Functional Framework Diagram  7.5 Application CircuitVIII Programming Guide  8.1 mBlock Programming  8.2 Arduino Programming  8.3 SchematicIX A Related Question about Light Sensor  9.1 Question  9.2 AnswerⅩ FAQII Definition2.1 What is a Sensor?In a broad sense, a sensor is a sensor that converts a measurement into a signal that can be perceived or quantified. In a narrow sense, a device that senses the measurement and converts it into an output signal of the same or another nature according to a certain law. The sensor is generally composed of a sensor element, a conversion element, a measurement circuit, and an auxiliary power source. The sensor element and the conversion element may be combined into one, and some sensors do not require an auxiliary power source.2.2 Definition of the Light SensorThe light sensor usually refers to a device that can sensitively sense the light energy of ultraviolet light to infrared light and convert the light energy into an electrical signal. The light sensor is a kind of sensing device, which is mainly composed of light-sensitive elements. It is mainly divided into four categories: ambient light sensor, infrared light sensor, sunlight sensor, and ultraviolet light sensor. It is mainly used in the field of changing body electronics applications and intelligent lighting systems. Modern electrical measurement technology is becoming more and more mature. Due to its advantages such as high accuracy and easy microcomputer connection for automatic real-time processing, it has been widely used in the measurement of electrical and non-electrical quantities.  However, the electrical measurement method is susceptible to interference. In the AC measurement, the frequency response is not wide enough and there are certain requirements on the withstand voltage and insulation. Today, the rapid development of laser technology has been able to solve the above problems.Figure1. Light SensorIII Spectrum and Photometric Physical Quantity3.1 SpectrumThe spectrum is a pattern in which monochromatic light, which is dispersed by the dispersive system (such as a prism and a grating), is sequentially arranged according to the size of the wavelength (or frequency). The largest part of the visible spectrum is the visible part of the electromagnetic spectrum of the human eye. Electromagnetic radiation in this wavelength range is called visible light. The spectrum does not include all the colors that the human brain can distinguish, such as brown and pink.Figure2. Spectrum3.2 Photometric Physical Quantities3.2.1 Light Intensity(I/Intensity)(1) Definition: the intensity of light emitted by a monochromatic light source (frequency 540 × 1012 Hz, wavelength 555nm) in a unit solid angle in a given direction (radiation intensity in this direction is 1/683 watts per spherical degree) .(2) Unit: cd (Candela)(3) Luminous intensity of common light sources:●  Sun, 2.8E27 cd●  Highlight flashlight, 10000 cd●  5mm super bright LED, 15 cd 3.2.2 Luminous Flux(F/Flux)(1) Definition: The energy emitted by a point light source or a non-point light source in a unit time. Among them, the visual person (radiation flux that humans can feel) is called luminous flux.(2) Unit: Lm (lumens)(3) Efficiency of common light sources (lumens / watt, Lm / W)● Incandescent, 15● White LED, 20● fluorescent lamp, 50● The sun, 94● Sodium lamp, 120 3.2.3 E/Illuminance(1) Definition: Luminous flux irradiated onto a unit area.(2) Unit: Lx / Lux (1), 1 (Lx) = 1 Lm / m2.(3) Common Illumination (Lx):● Direct sunlight (noon), 110,000● Overcast day, 1000● Inside the mall, 500● Cloudy room with window, 100● Under normal room lighting, 100● Full moon, 0.2 3.2.4 L / Luminance(1) Definition: The intensity of light emitted by the unit light source area in the normal direction and within the unit solid angle.(2) Unit: nt (nits), 1 (nt) = 1 cd / m2.(3) Brightness of common luminous body (nt):● Solar surface, 2,000,000,000● Incandescent filament, 10,000,000● White paper under the sun, 30,000● Brightness that human eyes can get used to, 3,000● The human eye can better distinguish the brightness of the color, 1● No moon night sky, 0.00013.3 MID Display's Perception of Backlight Brightness Under Different IlluminationFigure3. Ambient Illumination-LUXIV How the Light Sensor WorksThe light sensor actually works according to the principle of the photoelectric effect. The so-called photoelectric effect refers to the phenomenon that certain special substances can convert light energy into electrical energy after absorbing light. The photoelectric effect can be divided into two types: an external photoelectric effect and an internal photoelectric effect. The external photoelectric effect refers to the fact that under light irradiation, electrons can be emitted from the inside of the material to generate electricity. The photocell and photomultiplier are originals based on the external photoelectric effect.  Correspondingly, the internal photoelectric effect occurs inside the substance. When light is irradiated onto the substance, the resistivity inside the substance is changed, thereby generating electromotive force. Photoelectric elements such as photoresistors and photovoltaic cells are made based on the internal photoelectric effect. Take the light sensor on the mobile phone as an example:The light sensor in a mobile phone should actually be an ambient light sensor, which is mainly composed of two parts, a light projector, and a light receiver. The white dot next to the front camera acts as a lens that focuses the light in the environment and transmits it to the receiver via the projector. According to the photoelectric effect, the light receiver can convert various light signals into corresponding electrical signals, and then further process them into various switching and control actions to realize the sensitivity adjustment of the mobile phone. An infrared cut-off film is often attached to the chip of the ambient light sensor to eliminate the interference of infrared light so that our electronic devices such as mobile phones and laptops can accurately detect the visible light intensity in the environment. When the display consumes too much power, the light sensor can also automatically reduce the screen brightness to extend the operating time of the battery. Figure4. Light Sensor in PhoneV Types and Characteristics of Light Sensors5.1 Photodiode TypePhotodiodes and semiconductor diodes are similar in structure, and their die is a PN junction with photosensitive characteristics, which has unidirectional conductivity, so a reverse voltage needs to be added when working. When there is no light, there is a small saturation reverse leakage current, that is, a dark current, at which time the photodiode is turned off. When exposed to light, the saturation reverse leakage current greatly increases, forming a photocurrent, which changes with the intensity of the incident light. When light irradiates the PN junction, an electron-hole pair can be generated in the PN junction, which increases the density of minority carriers. These carriers drift under the reverse voltage, causing the reverse current to increase. So you can use the light intensity to change the current in the circuit. It is turned off when there is no light and turned on when there is light. Features:(1) High sensitivity can reduce the influence of stray light(2) Photodiode (photodiode) is a photoelectric conversion device, which can convert the received light into a current change(3) The working mode of the photodiode (photodiode) is to increase the reverse voltage or not increase the voltage. When a reverse bias is applied to it, the reverse current in the tube will change with the intensity of the light. The greater the light intensity, the greater the reverse current.Figure5. Photodiode5.2 Photoresistor Type(1) PrincipleIt works based on the semiconductor photoelectric effect. The photoresistor is non-polar and is purely a resistive element. It can be applied with DC voltage or AC voltage.(2) Working characteristics of the photoresistor: When the light is on, the resistance is small; when the light is off, the resistance is large. The stronger the light, the smaller the resistance; when the light stops, the resistance returns to its original value.(3) Spectral range: from ultraviolet to infrared.(4) Features:● The internal photoelectric effect has nothing to do with the electrode (only related to the photodiode), that is, a DC power supply can be used.● Sensitivity is related to the semiconductor material and the wavelength of the incident light● Epoxy resin package, high reliability, small size, high sensitivity, fast response speed, and good spectral characteristics.Figure6. PhotoresistorVI Applications of Light Sensors6.1 Types of Light Sensors in Application(1) Ambient light sensorThe ambient light sensor can sense the surrounding light conditions and tell the processing chip to automatically adjust the backlight brightness of the display to reduce the power consumption of the product. On the other hand, the ambient light sensor helps the display provide a soft picture. When the ambient brightness is high, the LCD monitor using the ambient light sensor will automatically adjust to high brightness. When the external environment is dark, the display will be adjusted to low brightness to achieve automatic brightness adjustment. (2) Infrared light sensorThe infrared light sensor uses a charged thermopile and a scandium bromide iodide (KRS-5) window to sense wavelengths from 580 to 40,000 nm. The sensor can be used to measure a range of phenomena, including infrared radiation from the palm of your hand. (3) Sunlight sensorSolar sensor. It can recognize horizontal and vertical 360 degrees. The location of the sun, identification, cloudy, cloudy, semi-cloudy, sunny and evening during the day. Tracking bearing identification. Identification circuit processing and server drive. A digital chip is used to complete the processing of the above information. It can serve a variety of ordinary motors, stepper motors. The power consumption of the whole machine is 3mA, and the chip working voltage is 5V.  International advanced solar tracking equipment uses computer data theory, which requires data and settings for the latitude and longitude of the earth. The circuit principle and equipment technology are complicated. Intelligent sun tracker uses recognition theory technology, simple circuit and few components, no theory of latitude, longitude and data information. There is no need to consider the route that the sun runs through the year. From which direction the sun rises and from which direction it falls, it can accurately identify the position where the sun rises and falls. If he is placed on a walking car or boat, the tracker can face the sun no matter where he goes. (4) UV light sensorThe UV light sensor uses a filter to measure the UV light band (315nm-400nm). Remove the filter, the sensor can sense visible light at the same time. The sensor includes a UV filter, a sight, and a sensor handle. Figure7. Types of Light Sensors6.2 Typical ApplicationsBacklight adjustment: TV, computer monitor, LCD backlight, mobile phone, digital camera, MP4, PDA, GPS;Energy-saving control: outdoor advertising machines, induction lighting appliances, toys; instruments and meters: instruments and industrial controls for measuring light intensity;Environmentally friendly replacement: Replace traditional photoresistors, photodiodes, phototransistors6.3 Practical Application Cases6.3.1 Changing Body Electronics Applications(1) Ambient light detectionIn body electronics applications, ambient light sensors are used to adjust the backlight intensity of the dashboard, as well as the LCD backlight intensity in navigation systems (GPS), temperature control, and DVD screens. This is especially important for displays like BMW's iDrive and Prius' Multi-Info. For example, when daylight becomes dim and dark, the dashboard backlight will be adjusted to varying degrees to achieve the best visibility and reduce the glare that may be caused to the driver. Using these sensors eliminates the problem of turning on the headlights during the day, and the display automatically adjusts brightness. The key function of the ambient light sensor is to use the sensitivity visible wavelength of 380nm ~ 780nm to replicate the sensitivity of the human eye. (2) Tunnel detectionTunnel detection requires the input of two sensors. The first sensor has a wider field of view "looking up" and a relatively long average moving period, which prevents the lights from turning on and off. The second sensor has a narrower field of view "looking forward" and a relatively short average moving time. This allows the tunnel sensor to respond quickly to sudden changes in daylight, turn on the car's headlights, and adjust the display's backlight brightness when entering the tunnel. Forward-facing sensors eliminate the need to turn lights on and off when entering under a bridge or a tree covering the sun. In these cases, the sensor will still "see" the light ahead. When entering the tunnel, the signal from the tunnel sensor will drop, while the signal from the wide-field sensor will remain high; the headlights of the car will be turned on. When exiting the tunnel, the signal from the tunnel sensor will increase and the signal from the wide field of view sensor will decrease; the headlights of the vehicle will be turned off. With different average moving periods, the controller makes a clear distinction. 6.3.2 Intelligent Lighting SystemTo improve the comfort of the working environment, the lighting control system adopts a light sensor to automatically control the lighting equipment according to the illuminance of the current environment, so that the illuminance is controlled within a comfortable range. In traditional lighting control systems, ordinary light sensors are often combined with A / D converters (ADCs). Because the light signal detected by the light sensor contains both visible light components and infrared light components, the infrared light is filtered to detect the light sensor detection results.VII The Circuit Diagram of a Light Sensor7.1 Model IntroductionThe light sensor shown below is a low-cost I2C digital light sensor (ALS), which can convert light intensity into a digital output signal that can directly interface with I2C, providing a wide dynamic range from 0.01lux to 64K lux The linear response is very suitable for applications under high ambient brightness.Figure8. Model7.2 Appearance and SizeFigure9. Appearance and Size of the model7.3 Application(1) Back-lighting Control in mobile / portable devices(2) Touch Panel Control in mobile / portable devices7.4 Functional Framework DiagramFigure10. Functional Framework Diagram7.5 Application CircuitFigure11. Application CircuitVIII Programming GuideThe programming described below is based on the Me light sensor developed based on the photoelectric effect principle in semiconductors.8.1 mBlock ProgrammingThe light sensor module supports the mBlock programming environment. The following is a brief description of the module instructions:Figure12. Programming GuideHere is an example of how to use mBlock to control a light sensor moduleWhen the LED receives the light, M-Panda will move left and right and say I love sunshine; Cover the LED light, M-Panda will stop moving and say I love night. The results are as follows:Figure13. Result8.2 Arduino ProgrammingIf you write a program using Arduino, you should call the library Makeblock-Library-master to control the Me Light Sensor. This program instructs Me Light Sensor to read the current light intensity through Arduino programming.Figure14. Arduino ProgrammingFunction list of light sensor:Figure15. Function List of Me Light Sensor8.3 SchematicFigure16. SchematicIX A Related Question about Light Sensor9.1 QuestionHow to combine these 2 circuits together so that during complete darkness on the LDR, the LED would turn on instantly and when light falls on the LDR there would be around a 1 or 2-second delay before completely shutting off?The circuit would be running on a 5V DC power supply and powering an LED array.How to combine them together? Figure17.Circuit1Figure18. Circuit29.2 AnswerIn the 555 circuit the capacitor controls the wait time, if the capacitor is short-circuited the circuit will wat forever.In the LDR circuit the transistor acts like a switch but unfortunately it's switching to ground but the capacitor in the 555 circuit is connected to +9VTo resolve this I swapped the parts in the 555 circuit upside down to have the capacitor to ground. Then it was simple to I merge the two circuits.Figure19. AnswerIn the dark R1 turns Q1 on the keesp C1 duscharged so 555 output will be high.when there is light the LDR turns Q1 off and C1 charges , once it gets enough charge the 555 output goes low.We could have instead built the upside-down version of the LDR circuit using a BC557 transitor (or other similar PNP type) instead of the BC547 NPN transistor and merged that with the original 555 circuit.Ⅹ FAQ1. How is a relay added to a light sensor circuit?Presumably, your light sensor will be generating a variable voltage signal in response to how much light is hitting it, and you want to trip a relay when this light is above (or possibly below) a threshold. One way to do this is with a comparator circuit, which will compare two voltages and output a high or low depending on which one is higher. You then compare the signal from the light sensor to a reference voltage that you can set with a potentiometer and generate a high or low output signal from that. You can also use a microcontroller and read the signal from the light sensor with an analog input pin. This is more complex but useful if you want to implement features like hysteresis in the comparison. Now, the logic level signal can’t drive a relay coil directly, so you will need to use a transistor to switch the relay coil current. Which transistor to use will depend on the voltages involved and the amount of current you need to switch, but it’ll be a small signal transistor of some kind. You also need a current limiting resistor on the gate, possibly a pull-down on the gate as well, and a flyback diode across the relay coil. 2. What is a light sensor?Light sensors respond to changes in infrared light to detect motion or proximity to another object. Proximity sensors help robotic machines navigate obstacles and avoid bumping into objects. They are also used for devices in vehicles that sound an alarm when the vehicle is close to bumping into an object. 3. What are the disadvantages of a light sensor?Following are the disadvantages of Light sensor :• LDRs are highly inaccurate with high response time (about 10s or 100s of milliseconds).• Resistance varies continuously (analog) in photoresistors and is rugged in nature.• Photodiodes are temperature sensitive and are uni-directional, unlike photoresistors. 4. What does a light sensor do?Light sensors are electronic devices that indicate the intensity of daylight or artificial light. They convert light energy to electrical signal output. Light sensors have several uses in industrial and everyday consumer applications. 5. Where are light sensors used?Light sensors have a lot of uses. The most common use in our daily lives is in cell phones and tablets. Most portable personal electronics now have ambient light sensors used to adjust brightness. 6. How many types of light sensors are there?By using LDR as a circuit, we can calibrate the changes in its resistance to measure the intensity of Light. There are two other Light Sensors (or Photo Sensors) that are often used in complex electronic system design. They are Photo Diode and Photo Transistor. All these are Analog Sensors. 7. How long does a light sensor last?Long Duration Settings – In most cases, your motion detector light should only stay on for 20 to 30 seconds after it's triggered. However, you can manipulate the settings so it will stay on longer. For example, many lights come with settings ranging from a few seconds to an hour or more. 8. Is a light sensor analog or digital?Analog sensors that are used for detecting the amount of light striking the sensors are called light sensors. These analog light sensors are again classified into various types such as photo-resistor, Cadmium Sulfide (CdS), and, photocell. 9. What is a light sensor in a phone?Ambient-light sensors (ALS) are widely used in smartphones to provide information about ambient-light levels, in support of the backlight LED power circuit. 10. How do you wire a light sensor to an outside light?Connect one black wire on the photocell to the black wire that comes from the building. Be sure to twist the exposed copper wire so that it forms a tight connection. Connect the second black wire on the photocell to the black wire on your light fixture, making sure that the copper wire is twisted together completely.  

IntroductionLED is a new type of light source that has entered the application field in the past ten years, and it has been used in the medical field for about 6 years, showing excellent therapeutic effects in such a short period of time. LED is a cold light source, which can well moisturize the skin while treating diseases. Besides, since high-power LEDs have strong light intensity and a good effect on the deep layer of the human skin, they are widely used in various departments in hospitals. The LED light sources currently used in the medical field include red, blue and purple. The efficacy of LED in disinfection and sterilization, wound healing, wound treatment, inflammation elimination, edema reduction, and photodynamic tumor treatment has been fully affirmed in the medical field. Can LED Light Improve Your Skin?CatalogIntroductionCatalogI What is LED Light Therapy? Is it Safe?  1.1 LED  1.2 LED Light Therapy  1.3 Safety&Side EffectsII LED Light Therapy Colors: Which do you Need?  2.1 Does LED Light Therapy Actually Work?  2.2 How to Choose the LED Light Therapy Colors?III Specific Uses and Benefits of LED Light TherapyIV Procedure of Performing a LED Light Therapy  4.1 Perform a LED Light Therapy at a Professional’s Office  4.2 How to use At-home Devices?V LED Light Face Mask  5.1 Does LED Light Face Mask Work?  5.2 Are LED Face Masks Safe?VI Frequently Asked QuestionsI What is LED Light Therapy? Is it Safe?1.1 LEDLED is the abbreviation of Lighting emitting diode, which is a light-emitting diode, which is made of compounds containing gallium (Ga), arsenic (As), phosphorus (P), nitrogen (N), etc. Semiconductor. When electrons and holes are recombined, they can radiate visible light, so they can be used to make light-emitting diodes. The gallium arsenide diode emits red light, the gallium phosphide diode emits green light, the silicon carbide diode emits yellow light, and the gallium nitride diode emits blue light. Light-emitting diodes appeared as early as 1962. In the early days, it could only emit low-light red light, and later developed other monochromatic light versions. The light that can be emitted today has reached visible light, infrared light and ultraviolet light, and the light level has increased to a considerable level Degree.Figure1. LED 1.2 LED Light TherapyFor many years, scientists have studied how the sun's rays, including so-called burning rays of the sun, or ultraviolet B radiation, ultraviolet A rays, or UVA, affect the skin. Only recently have we started to talk about the effects of visible light on the skin — not necessarily LED light, but visible light in general," says Dr. Buzney, assistant professor of dermatology at Harvard Medical School. LED lights have been around since the 1960s, but have only recently been used as a skin treatment that uses varying wavelengths of light, including red, purple, green and blue. Different wavelengths of the visible light spectrum correspond to different colors of LED light and penetrate the skin to different depths. Depending on how deeply they penetrate, LED lights are thought to have different biological effects.1.3 Safety&Side EffectsAccording to Harvard Health Publishing, for the most part, these LED light therapies appear to be relatively safe, at least in the short term. The FDA has approved some products for home use. LED skin devices don't have a lot of power, so they're unlikely to burn our skin. However, it is important to shield your eyes from the light while using them. In addition, a recent study named Phototherapy with Light Emitting Diodes indicates that a device using LEDs with frequencies of 415nm (blue), 633nm (red), and 830nm (infrared) has demonstrated significant results for the treatment of medical conditions, including mild-to-moderate acne vulgaris, wound healing, psoriasis, squamous cell carcinoma in situ (Bowen’s disease), basal cell carcinoma, actinic keratosis, and cosmetic applications.  Although photodynamic therapy with the photosensitizer 5-aminolevulinic acid might cause stinging and burning, phototherapy is free of adverse events. We determined that phototherapy using LEDs is beneficial for a range of medical and aesthetic conditions encountered in the dermatology practice. This treatment displays an excellent safety profile. The above content is extracted from the journal directly, Let’s put it simple:● In the short term, LED light therapies are relatively safe, but you have to care about the device's potential to damage the eyes, especially for people with underlying eye conditions or those who are taking medication that makes the eyes more sensitive to light.● Light Therapy doesn't use UV light so there's no risk of tanning whatsoever. Therefore, you do not have to worry for regular use.● LED light therapy doesn’t cause burns compared to other anti-aging treatments such as chemical peels, dermabrasion, and laser therapy. In general, side effects are rare, but there may be(1) increased inflammation(2) Redness(3) Rashes(4) TendernessYou should not use LED therapy if having taken certain medications, such as isotretinoin (Accutane), for acne or use topical treatments that cause sensitivity to sunlight. People with skin conditions should speak to a dermatologist before using LED light therapy.Figure2. LED Light TherapyII LED Light Therapy Colors: Which do you Need?2.1 Does LED Light Therapy Actually Work?The light therapy effect of LEDs is based on the wavelengths of different spectra. Red light LEDs of 633nm to 660nm can promote collagen proliferation of the skin and even lighten fine lines and dark spots. Near-infrared LEDs with a wavelength of 780nm to 1200nm can be used Anti-inflammatory and analgesic. The blue LED and the green LED can also be used in the medical beauty market, which are respectively suitable for preventing the growth of acne and brightening, helping to absorb nutrients in skin care products, and improving the effect of allergic skin. Laura Ferguson, founder of The Light Salon, a company focused on LED beauty, said that LED light therapy has many benefits, different effects at different wavelengths, such as anti-wrinkle or blemish, and the light will not have a band that will damage the skin Intrusive, painless light therapy, it even has a mood-relieving effect. Ferguson said that LED can also solve the problem of skin sensitivity. After light therapy, the newly stimulated cells will have a protective layer to help prevent sunburn from being exposed to strong sunlight. LED light therapy is not like a solarium, so you don't have to worry about melanin precipitation. However, the current price of LED medical beauty products is still high. In the future, the price is expected to decline as the technology of LED medical products matures. At that time, consumers' choices and needs will be more and more diversified. Figure3. Four Types of LED Light2.2 How to Choose the LED Light Therapy Colors?LED light stimulates fibroblasts, which can produce collagen, thereby improving skin elasticity, scarring and enhancing skin metabolism. It can also make use of the organism's absorption of different visible light wavelengths to stimulate the mitochondria and glands to produce more energy and extend the life cycle of cells. LED light can be used in all parts of the human body, whether it is psychological or physical, scalp or toes, internal medicine or surgery, as long as the light reaches the place, it can be used for effective treatment. After laser and pulsed light, LED light therapy has become a new light therapy. (1) Red lightThe red light with a wavelength of 635nm has the characteristics of high purity, strong light source, and uniform energy density. Red light has bactericidal, repairing and pain-removing effects, which can increase cell activity and promote cell metabolism. (2) Blue LightBlue light with a wavelength of 405, 415nm has a strong bactericidal effect, which can quickly inhibit inflammation. During the formation of acne, it is mainly caused by Propionibacterium, and blue light can cause no damage to skin tissue, effectively destroy this bacteria. (3) Purple LightThe violet light with a wavelength of 313, 410nm has the advantages of sterilizing, purifying the skin, activating cells, and promoting protein and collagen synthesis. It has a good effect on specific dermatitis, vitiligo, scleroderma and so on. (4) Green Light (560nm)Natural and soft light color, which has the effect of neutralizing and stabilizing nerves, can improve anxiety or depression; regulate skin gland function, effectively dredge lymph and improve edema, improve oily skin, acne, etc. Figure4. Function of Diffrent Light III Specific Uses and Benefits of LED Light Therapy(1) PhotorejuvenationPhoton skin rejuvenation technology is defined as non-exfoliation skin rejuvenation treatment using low-energy density under continuous high pulse light. At present, it has become one of the main methods to improve skin photoaging. This technology can significantly improve skin wrinkles and texture.  Rough, irregular pigmentation and enlarged pores.Such phenomena have been recognized by many technical professionals and beauty applicants. The characteristic histological changes of skin photoaging are elastic fibrosis and collagen fiber maturation disorder in the dermal matrix, which leads to skin relaxation and wrinkles. The study found that visible to near-infrared LED light penetrated the epidermis of the skin and reached the dermal layer of the skin, and promoted the regeneration and rearrangement of elastic fibers and collagen fibers through photothermal and photochemical effects, thereby reducing skin wrinkles and increasing elasticity. (2) Prevent or treat pigmentation after inflammationPigmentation of skin after inflammation is a common and difficult to avoid phenomenon in skin physical and chemical cosmetology, and it is especially easy to appear in Asian people. For example, in order to reduce the degree of skin pigmentation after laser treatment in the clinic, generally avoid the season of excessive ultraviolet rays, ask patients to avoid sun, apply sunscreen, etc., but it is still difficult to completely avoid pigmentation after inflammation. Recent studies have found that 660nm LED light can prevent or even treat skin pigmentation that occurs after this inflammation, which will be a new research hotspot in the skin and beauty industry. (3) Promote wound healingIt can be seen that LED light of various wavelengths in the near infrared can promote the growth of epithelial cells after trauma, and promote wound healing. At the same time, it also has a good therapeutic effect on the healing of chronic ulcers in the lower extremities of diabetic patients. (4) Reduce inflammationA series of studies have shown that LED has anti-inflammatory effects. Research has found that 635nm LED light can inhibit the release of the inflammatory mediator prostaglandin E2 (PGE2) by the fibroblasts of the gum, thereby reducing the inflammatory response of the gum. Before using pulsed dye laser to treat skin photoaging, if LED light source is used to irradiate in advance, it can reduce the discomfort of skin erythema, swelling and pain caused by dye laser. The use of LED light sources in advance of radiation therapy for breast cancer patients can reduce the side effects of radiotherapy. (5) Scar preventionKeloid keloids is a skin disorder that affects beauty and is difficult to treat clinically. It is caused by excessive proliferation of connective tissue after skin damage. Patients often have a scarring constitution. It started clinically as a small, hard red pimples, which slowly increased, producing round, oval, or irregular scars, higher than the skin surface, extending outward in the shape of a crab foot, with smooth and shiny skin, which may be accompanied by Pain, itching, etc. The clinical treatment is difficult and the effect is not ideal. Studies have found that LED can significantly improve the patient's pain, itching and other discomfort, make the scar flat, and have the advantages of non-invasive. (6) Other functionsIn addition, LED can also be used as a non-ultraviolet light therapy instrument, used in photodynamic therapy, hair loss treatment, skin damage reduction after ultraviolet irradiation, and so on. In short, LED as a new type of light source has been gradually applied to dermatology. With the continuous innovation of LED lamps and the study of the biological effect of LED on medicine, the application of LED in dermatology will have unlimited prospects. . At the same time, LEDs have higher security and can be used more widely as home medical equipment.Figure5. LED Light Therapy DevicesIV Procedure of Performing a LED Light Therapy4.1 Perform a LED Light Therapy at a Professional’s OfficeWhen getting an LED treatment, you really don’t have to do much but lie in a comfy bed with your face positioned directly under panels that emanated different colored lights. Generally, LED panels will be placed a few inches away from your face after microneedling or microdermabrasion. Each session lasts approximately 15-20 minutes. At first, it feels warm, and many people report it is really like the feeling of relaxation.4.2 How to use At-home Devices?Using at-home light therapy devices is like working out by yourself and things done in the office are like working out with a trainer. Both are good. But you’re not going to get as intense of a treatment at home. This means at-home LED devices may be more convenient, but they may be less effective than professional treatments. When using an at-home device, it is important to follow the manufacturer’s instructions. These devices typically come in the form of a mask that a person applies to the face for several minutes or a wand that they use on the skin. LED light therapy is suitable for use on any body part, including the face, hands, neck, and chest.Following treatment, no recovery time is necessary.Does LED Light Therapy Really Work? Can You Do it At HOME?V LED Light Face Mask5.1 Does LED Light Face Mask Work?The LED mask was invented by John Tsagaris, a Chinese medicine doctor. It is understood that John has a degree in human biological sciences from Chinese Medicine, and also holds a graduate diploma in skin treatment and beauty care. LED blue light can play a bactericidal and anti-inflammatory effect to improve the surface skin, and has a good effect on the treatment of acne and rosacea. LED red light can promote the growth of skin collagen, for deep skin beauty care. The working principle of LED mask is similar to photosynthesis. It treats skin folds from the depth by changing the energy of LED red light. It can not only calm the skin, but also prevent the growth of bacteria inside the skin. The use of LED mask masks not only does not have a claustrophobic feeling, but the LED red light delivered to the skin in large quantities can make people feel comfortable. Just wear the LED mask for 25 minutes every day, and the LED red light can gradually improve your skin. According to a survey report from the United States, LED masks have a significant effect on eliminating wrinkles. Another report showed that 90% of people believe that LED mask can reduce skin aging, make the skin more delicate and smooth, and greatly improve the crow's feet, red blood, and melanin deposition in the corners of the eyes.Figure6. Depth of Light Energy Penetration5.2 Are LED Face Masks Safe?Actually, it is the same concern as whether LED light therapy is safe. There’s no doubt that one of the most important aspects of LED phototherapy devices is their safety. Phototherapy with Light Emitting Diodes also points out that LEDs are nonablative and nonthermal, and when used alone (i.e., without topical photosensitizers in PDT applications) do not cause damage to the epidermis or dermal tissue.  There are no adverse events associated with the use of these devices and little to no downtime for the patient. When LED phototherapy is used alone, patients do not experience redness, peeling, blistering, swelling, or pain. In fact, patients can have a treatment during their lunch hour and return to work immediately afterwards. While home use devices have been available for several years, there are many differences between those devices and those specifically designed for use by physicians. The home use devices necessarily deliver significantly less power and typically do not have light panel arrays large enough to treat the entire face at once, for example. As they often are hand-held, it might be cumbersome, time-consuming, and impractical to treat the entire face in a single session.  In contrast with the medical LED units and their protocols, home use devices have not been validated by controlled clinical studies published in peer-reviewed journals. In some cases, home units may be used adjunctively with dermatologist-provided treatment to address specific areas of concern, but they are dissimilar enough from the medical-grade units to not be considered an alternative to these tested technologies.Figure7. LED Face MasksVI Frequently Asked Questions1. Does LED light therapy actually work?LED light therapy appears to be a safe treatment for several skin conditions, including acne, skin aging, skin wounds, and other problems. Research indicates that this therapy offers promising results, although people should not expect a 100% improvement. 2. What does LED light therapy do?LED light therapy is now used by some aestheticians to help regenerate the skin from aging. It's also used for acne. Your healthcare provider uses red or blue light frequencies based on the skincare concern. Red is primarily used for anti-aging, while blue is used for acne treatment. 3. Does LED light reduce wrinkles?LED light therapy can stimulate collagen production, which reduces fine lines and wrinkles, as well as eliminate acne-causing bacteria, which improves skin clarity. 4. Can you overdo LED light therapy?Light therapy cannot be overdone for most people. If you notice any extraordinary results, stop treatment, and contact your physician. For the best results, choose the right device style and LED color, and use it as directed. 5. Does red light therapy tighten loose skin?Amber light stimulates collagen and elastin. Red light is most commonly used to promote circulation. White light penetrates the deepest and works to tighten and reduce inflammation. Blue light kills bacteria. 6. Are LED lights bad for your eyes?New findings confirm earlier concerns that "exposure to an intense and powerful [LED] light is 'photo-toxic' and can lead to irreversible loss of retinal cells and diminished sharpness of vision," the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) warned in a statement. 7. Are led masks effective?The research behind LED masks is centered on the lights used, and if you're going on those findings, LED masks can be beneficial to your skin. 8. What are the side effects of red light therapy?Red light therapy is considered safe and painless. However, there have been reports of burns and blistering from using RLT units. A few people developed burns after falling asleep with the unit in place, while others experienced burns due to broken wires or device corrosion. 9. Is red light therapy the same as laser therapy?In clinical practice, low-level laser (LLT) therapy involves exposing tissues to red and near infrared (NI) light, which are lower in energy than the lasers used in surgery. 10. How long does it take for light therapy to work?Light therapy can start to improve symptoms within just a few days. In some cases, though, it can take two or more weeks.

I IntroductionLaser sensor is a kind of sensor which uses laser technology to measure. It is generally composed of laser, optical parts and photoelectric devices. It can convert the measured physical parameters (such as length, flow, speed, etc.) into optical signals, and then use photoelectric converter to convert the optical signals into electrical signals. Through the filtering, amplification and rectification of corresponding circuits, the output signals can be obtained, so as to calculate the measured quantity. Laser technology has the characteristics of strong direction, high brightness and good monochromaticity. It is widely used in industrial and agricultural production, national defense and military, medical and health, scientific research and other aspects, such as distance measurement, precision detection, positioning, etc., as well as length benchmark and optical frequency benchmark.Laser Distance Sensor OverviewCatalogI IntroductionII What is Laser? 2.1 The Concept of Laser 2.2 Important Characteristics of Laser 2.3 Types of Laser 2.4 What can Laser Sensor Detect?III Laser Displacement Sensor 3.1 What is Laser Displacement Sensor 3.2 How Does Laser Displacement Sensor Work? 3.3 Application of Laser Displacement Sensor 3.4 What are the Parameters to Know When Choosing a Laser Displacement Sensor?IV Laser Distance Sensor 4.1 Classification of Laser Distance Sensors  4.2 Measuring Principle of Different Laser Distance Sensors 4.3 Application of Laser Distance SensorV Laser Sensor Application CaseVI FAQII What is Laser?2.1 The Concept of LaserLaser light is different from ordinary light. (See more about light and photoelectric effect in the article introducing light sensor and photoresistor)We need to use laser to produce laser light. In the normal state, most of the atoms in the laser are in stable low energy level E1. Under the action of appropriate frequency of external light, the atoms in low energy level absorb photon energy to excite and transition to high energy level E2. The photon energy E = e2-e1 = h V, where h is the Planck constant and V is the photon frequency.  On the contrary, when the frequency of light is V, the atom in level E2 will jump to the low energy level to release energy and emit light, which is called stimulated radiation. First of all, the laser makes the atoms of the working materials abnormally in the high-energy level (i.e. inversion distribution of the particle number ), which can make the stimulated radiation process dominant, so that the induced light with the frequency of V can be enhanced, and the large stimulated radiation light can be produced through the avalanche amplification of the parallel reflector, which is called laser light for short.Figure1. Laser2.2 Important Characteristics of Laser（1）High directivity, small divergence angle of light speed, the laser beam extends only a few centimeters from a few kilometers away.（2）High monochromaticity, the frequency width of laser light is more than 10 times smaller than that of ordinary light.（3）High brightness, laser beam convergence can produce temperatures up to several million degrees.2.3 Types of LaserLaser can be divided into four types according to working substance:（1）Solid state laserIts working substance is solid. Ruby laser, neodymium doped yttrium aluminum garnet laser (i.e. YAG laser) and neodymium glass laser are commonly used. Their structures are basically the same, characterized by small and solid, high power. At present, neodymium glass laser is the device with the highest pulse output power, which has reached tens of megawatts.（2）Gas laserIts working substance is gas. Now there are various kinds of gas atoms, ions, metal vapor, gas molecular lasers. Commonly used are carbon dioxide laser, helium neon laser and carbon monoxide laser, whose shape is like a common discharge tube, characterized by stable output, good monochromaticity, long life, but small power, low conversion efficiency.（3）Liquid laserIt can be divided into chelate laser, inorganic liquid laser and organic dye laser, the most important of which is organic dye laser. Its main feature is that the wavelength is continuously adjustable.（4）Semiconductor laserIt is a younger laser, and the more mature one is GaAs laser. It is characterized by high efficiency, small size, light weight and simple structure, and is suitable for carrying on airplanes, warships, tanks and infantry. It can be made into range finder and sighting device. However, the output power is small, the directivity is poor, and it is greatly affected by the ambient temperature.2.4 What can Laser Sensor Detect? (1) Laser measurement of lengthPrecise measurement of length is one of the key technologies in precise machinery manufacturing industry and optical processing industry. Modern length measurement is mostly based on the interference phenomenon of light wave, and its accuracy mainly depends on the monochromaticity of light. Laser is the most ideal light source. It is 100 thousand times purer than the best monochromatic light source (krypton-86 lamp). Therefore, the laser measurement range of length is large and the accuracy is high.  According to the optical principle, the relationship between the maximum measurable length L of monochromatic light and wavelength λ and spectral line width δ is L = λ 2 / δ. The maximum measurable length of krypton-86 lamp is 38.5cm. For a long object, it is necessary to measure in sections to reduce the accuracy. If He-Ne gas laser is used, it can measure tens of kilometers at most. Generally, the length within several meters can be measured with an accuracy of 0.1 μ M.Figure2. Laser Measure(2) Laser measurement of distanceIts principle is the same as that of the radio radar. After the laser is aimed at the target, the round-trip time is measured, and then the round-trip distance is obtained by multiplying the speed of light. Because of the advantages of laser, such as high directivity, high monochromaticity and high power, these are very important for the measurement of long distance, the determination of target orientation, the improvement of signal-to-noise ratio of the receiving system, and the guarantee of measurement accuracy, so the laser rangefinder is paid more and more attention.  The lidar developed on the basis of the laser rangefinder can not only measure the distance, but also the azimuth, velocity and acceleration of the target. It has been successfully used in the ranging and tracking of the artificial satellite. For example, the lidar using ruby laser has a distance measuring range of 500-2000 km with an error of only a few meters. At present, ruby laser, neodymium glass laser, carbon dioxide laser and Gas laser are often used as the light source of laser rangefinder.Figure3. Measuring Distance with Laser Sensor (3) Laser measurement of thickness Based on the principle of triangle ranging, a precise laser ranging sensor is divided at the upper and lower part of the C-frame. The modulated laser emitted by the laser hits the surface of the measured object. By sampling the signal of the linear CCD, the distance between the measured object and the C-frame is synchronously obtained by the linear CCD camera under the control of the control circuit. The thickness of the middle measured object is calculated by the data fed back by the sensor. Because the detection is continuous, the continuous dynamic thickness of the measured object can be obtained.Figure4. Thickness Measuring with Laser SensorThickness measurement by single laser displacement sensorPut the measured body on the measuring platform, measure the distance from the sensor to the platform surface, then measure the distance from the sensor to the measured body surface, and measure the thickness after calculation. It is required that there is no air gap between the measured body and the measuring platform, and the measured body is not cocked. These strict requirements can only be achieved offline.Thickness measurement by double laser displacement sensorA laser displacement sensor is installed above and below the measured body respectively, and the thickness of the measured body is d = C - (a + b). Among them, C is the distance between two sensors, a is the distance between the upper sensor and the measured body, and B is the distance between the lower sensor and the measured body. The advantage of this method for on-line thickness measurement is that it can eliminate the influence of the vibration of the measured body on the measurement results.  But at the same time, there are requirements for sensor installation and performance. The conditions to ensure the accuracy of measurement are that two sensor beams must be coaxial and that two sensor scans must be synchronous. Coaxiality is realized by installation, and synchronization depends on the selection of laser sensor with synchronization end.Figure5. Thickness MeasurementIII Laser Displacement Sensor3.1 What is Laser Displacement SensorThe laser displacement sensor is called the eyes of the robot and machine, and has an irreplaceable role in welding, blank manufacturing, mechanical processing, heat treatment, loading and unloading, assembly and other operations. So, what is a laser displacement sensor? The laser displacement sensor is a sensor that uses laser technology for measurement, and is composed of a laser, a laser detector, and a measurement circuit. As a new type of measuring equipment, the laser displacement sensor can accurately measure the position, displacement and other changes of the measured object, and can also measure precise geometric measurements such as displacement, thickness, vibration, distance, and diameter.3.2 How Does Laser Displacement Sensor Work?The laser displacement sensor can accurately and non-contactly measure the position, displacement and other changes of the measured object, and is mainly used to measure the displacement, thickness, vibration, distance, diameter and other geometric quantities of the object. According to the measurement principle, the principle of laser displacement sensor is divided into laser triangulation method and laser echo analysis method. Laser triangulation method is generally suitable for high-precision and short-distance measurement, while laser echo analysis method is used for long-distance measurement. The following is the introduction to two measurement methods of laser displacement sensor principle.TriangulationFigure6. Laser Displacement SensorThe laser emitter shoots the visible red laser to the object surface through the lens, and the laser reflected by the object passes through the receiver lens, which is accepted by the internal CCD linear camera. According to different distances, the CCD linear camera can "see" this light point at different angles. According to the distance between the laser and the camera known from this angle, the digital signal processor can calculate the distance between the sensor and the measured object. At the same time, the position of the beam in the receiving element is processed by analog and digital circuits, and the corresponding output value is calculated by microprocessor analysis, and the standard data signal is output in proportion in the analog quantity window set by the user. If switching value output is used, it will be conducted in the settings window and cut off outside the window. In addition, an independent detection window can be set for analog quantity and switch quantity output.Echo analysisThe laser displacement sensor can achieve a certain degree of accuracy by using the echo analysis principle to measure the distance. The sensor is composed of processor unit, echo processing unit, laser transmitter and laser receiver. The laser displacement sensor emits one million pulses per second through the laser transmitter to the detector and returns to the receiver. The processor calculates the time required for the laser pulse to meet the detector and return to the receiver, so as to calculate the distance value.  The output value is the average output of thousands of measurement results. It is the so-called pulse time method. The laser echo analysis method is suitable for long-distance detection, but the measurement accuracy is lower than the laser triangulation method, and the longest detection distance can reach 250m.3.3 Application of Laser Displacement Sensor(1) Dimension measurement: position identification of small parts; monitoring of whether there are parts on the conveyor belt; detection of material overlapping and covering; control of manipulator position (tool center position); device state detection; detection of device position (through the small hole); monitoring of liquid level; thickness measurement; vibration analysis; collision test measurement; automobile-related test, etc. (2) Thickness measurement of sheet metal: laser sensor measures the thickness of sheet metal. Thickness change detection can help to detect wrinkles, small holes or overlaps to avoid machine failure. (3) Cylinder measurement: angle, length, eccentricity of inner and outer diameter, conicity, concentricity and surface profile.Figure7. Application of Laser Displacement Sensor(4) Length measurement: place the measured component on the conveyor belt at the designated position, the laser sensor detects the component and simultaneously measures it with the triggered laser scanner, and finally obtains the length of the component. (5) Uniformity check: place several laser sensors in a row in the tilt direction of the workpiece movement to be measured, and directly output the measurement value through one sensor. In addition, the software can be used to calculate the measurement value and read out the result according to the signal or data. (6) Inspection of electronic components: two laser scanners are used to place the tested components between them. Finally, the data is read out by the sensor, so as to detect the accuracy and integrity of the component size. (7) Inspection of filling level in production line: laser sensor is integrated into the production and manufacturing of filling products. When the filling products pass through the sensor, it can detect whether the filling is full. The sensor can accurately identify whether the filling product is qualified and the quantity of the product by using the extended program of laser beam reflecting surface. 3.4 What are the Parameters to Know When Choosing a Laser Displacement Sensor?Some parameters that must be understood when selecting a laser displacement sensor are very important.(1) Resolution: generally refers to the minimum range of the sensor, that is, the maximum recognition rate of the sensor. If the parameter is marked as 1mm, then the resolution is equal to 1mm. (2) Repeatability: We must know that even if the measured object is at rest, the measured value will fluctuate slightly. The error margin of repeated measurement of the measured object at the same position in the static state is the repeat accuracy. For example, if the parameter is marked as 1μm, the repeat accuracy of the sensor is 1μm. (3) Full range (effective range): the rated effective range of the sensor. When selecting a sensor, we must select the sensor that contains the effective range according to the required detection distance. (4) Linear accuracy: the error between the measured value and the actual displacement. Linear accuracy is expressed as a percentage, but since the range is a range and the measurement accuracy is more difficult to reach the apex of the range, most sensors will mark the linear accuracy of the apex of the range to intuitively reflect the performance of the sensor. (5) Sampling frequency/sampling period: frequency refers to the number of measurements per second. The higher the frequency, the shorter the time it takes to make a measurement. The shorter the measurement time, the more suitable it is for the detection of high-speed moving objects. (6) Average sampling times: even in the static state, there will be slight measurement fluctuations. At this time, multiple measurements are required to calculate the average number to make the measured value stable and accurate.Figure8. Laser SensorIV Laser Distance SensorLaser ranging is one of the earliest applications of the laser. This is because the laser has many advantages such as strong directivity, high brightness, and good monochromaticity. Before 1965, the Soviet Union used a laser to measure the distance between the earth and the moon (384401km) with an error of only 250m. In 1969, the Americans landed on the moon with a retro-reflector on the lunar surface. They also used a laser to measure the distance between the earth and the moon, with an error of only 15cm. The basic principle of using laser transmission time to measure the distance is to determine the target distance by measuring the time required for the laser to travel to and from the target.Related recommendation: Proximity SensorFigure9. Laser Distance Sensor4.1 Classification of Laser Distance Sensors Laser distance sensor technology is divided into absolute distance measurement method and micro displacement measurement method according to the measurement range. Subdivided according to the measuring method, the absolute distance ranging method mainly includes pulse laser ranging and phase laser ranging, and the micro displacement measuring method mainly includes triangulation laser ranging and interferometric laser ranging.4.2 Measuring Principle of Different Laser Distance Sensors(1) Pulse Laser Distance SensorA pulse laser with a very short duration is emitted by a pulsed laser, and after reaching the target to be measured after the distance to be measured, part of the energy will be reflected back. The reflected pulsed laser is called an echo. The echo returns to the rangefinder and is received by a photoelectric detector. According to the interval between the main wave signal and the echo signal, that is, when the laser pulse travels from the laser to the target to be measured, the distance of the target to be measured can be calculated.  (2) Phase laser Distance SensorThe emitted laser light is emphasized, and the phase change of the modulated signal is used when the laser is propagated in space. According to the wavelength of the modulated wave, the distance represented by the phase delay is calculated. That is, the indirect method of phase delay measurement is used instead of directly measuring the time required for the round trip of the laser to achieve distance measurement. The accuracy of this method can reach the millimeter level.Figure10. Working Principle of Laser Distance Measuring Device (3) Triangulation Laser Distance SensorAs mentioned above, this measurement principle is that the light emitted by the laser is focused on the surface of the measured object after being focused by the condensing lens, and the receiving lens receives the scattered light from the incident light spot and images it on the photoelectric  position detector On the sensitive side. When the object moves, the relative distance of the object movement is calculated by the displacement of the light spot on the imaging surface. The resolution of triangulation laser ranging is very high, which can reach the order of microns.   Figure11. Triangulation Principle (4) Interferometric Laser Distance SensorBy moving the measured target and measuring the coherence, the distance increment measurement is completed by counting, so the sensitivity of the interferometric measurement is very high, which can reach the nanometer level.4.3 Application of Laser Distance SensorThe laser distance sensor is mainly used for: monitoring the position of moving objects; measuring the railway contact network, measuring the boundary of buildings; measuring unsuitable objects; industrial automation and intelligent production management; vehicle speed and flow statistics; industrial monitoring signal trigger control; tower crane XY positioning of crane; automatic target distance control; monitoring of ship's safe docking position; positioning of container; measurement of vehicle's safe distance; measurement of overhead cable and height limitation; measurement of width of boxes on conveyor belt.V Laser Sensor Application Case(1) Over-limit detection of vehicle width and heightThe laser sensor is used for rapid measurement, the network core of the PC industrial control computer and the visual programming software VB are used for real-time data transmission and processing, and the friendly interface control software is also designed. Field test data shows that the system has good real-time performance and high measurement accuracy, and has certain practical value. (2) Expressway toll stationUsed in highway toll stations to count and protect vehicles. Malaysian Teras has applied hundreds of BEA laser sensors to its manual and automatic toll station systems. The laser sensor uses the time-of-flight (TOF) measurement principle, which can form 4 planes in the detection area to detect the vehicle. At the same time, the product also has functions such as anti-collision and vehicle safety protection. Compared with the traditional light curtain, the laser sensor has the advantages of high sensitivity, high accuracy, easy installation, high cost performance and strong stability. (3) Google's second-generation unmanned vehicleIn addition to the laser sensor on the top, Google’s second-generation driverless car prototype is still quite obvious, and the other sensors are set very concealed. The front, rear and sides of the vehicle are clearly marked with the Google unmanned vehicle logo. The driving principle of Google's unmanned vehicle is to continuously collect various accurate data of the vehicle itself and the surroundings through many sensors installed around the car, analyze and calculate it through the processor in the car, and then control the driving of the car according to the calculation results . Unmanned vehicles will use GPS equipment and sensors to accurately locate the vehicle's position and speed, and judge pedestrians, vehicles, bicycles, signal lights and many other objects around it.Figure12. Google's Self-driving CarThe roof of this Lexus is equipped with a 360° rotating laser holographic sensor, which can sense the front, side and rear conditions of the car almost simultaneously. The data collected by the sensor will be input to the processor located on the right rear side of the vehicle through the green data line. This laser sensor can also allow unmanned vehicles to be accurately positioned globally. The original L-shaped Lexus logo on the front of the car was also removed and replaced with a radar sensor; it was used to measure the distance ahead and the speed of the vehicle in order to determine the condition of the vehicle ahead and control the safe acceleration and deceleration of the vehicle. The wheel hub of the tire is also equipped with a position sensor, which is used to detect wheel rotation and help the vehicle to locate. The heart of Google's unmanned vehicles-the processor is located on the right rear side of the vehicle, the data information from each sensor will be transmitted here through the data wire, and analyzed and processed through the software in order to accurately sense and judge the difference between the unmanned vehicles object. In addition to analyzing and judging the current position of objects around the unmanned vehicle, the unmanned vehicle also needs to be calculated by software to accurately predict the possible next position of each object. Finally, the unmanned car will make safe driving decisions based on all the collected data, including controlling the speed of the car and the surrounding distance. VI FAQ1. How does laser sensor work?The basic principle is optical triangulation using a CMOS linear imager. A diffuse triangulating laser distance sensor transmits a laser through a lens and to the target, which reflects the light back to the sensor. A lens focuses this reflected light into a small spot onto the CMOS linear imager. 2. What is the use of laser sensors?The definition of a laser sensor is, it is an electrical device used to sense minute objects and precise positions. This sensor uses a laser to produce light within a straight line. Its visible ray mark of the laser makes the arrangement very simple. Laser light includes light waves with similar wavelengths. 3. What are the types of laser sensors?Laser distance sensors.Displacement sensors.Laser projectors.Laser light curtains.Laser photoelectric sensors.Positioning lasers.Laser edge detection sensors. 4. Are laser sensors dangerous?Improperly used laser devices are potentially dangerous. Effects can range from mild skin burns to irreversible injury to the skin and eye. The biological damage caused by lasers is produced through thermal, acoustical and photochemical processes. 5. Is a laser a sensor?A laser sensor uses a 'laser' to emit light in a straight line. Its visible beam spot makes alignment and positioning very easy. Since the light beam is focused, the sensor can be installed without worries about stray light. The major types of laser sensors include reflective, thru beam, and retro-reflective. 6. What is the range of the laser sensor?Laser distance sensors are designed for non-contact distance measurements: laser gauges for measuring ranges up to 10m, laser distance sensors for up to 3,000m. 7. What is CMOS Laser Sensor?A CMOS image sensor combines with a step-less laser power adjustment algorithm to produce stable detection of all types of workpieces from black rubber with low reflectivity to stainless steel and other highly glossy materials. 8. Which laser sensor is used for measuring very long distances?LDM301 laser distance sensor series – fast measurement of long distances. The laser distance sensors of the LDM301 series use a measured time-of-flight principle to measure distances of 300 m for natural surfaces and 3,000 m for reflective surfaces. 9. How does a laser sensor measure distance?The distance measurement is based on the triangulation principle. The laser beam strikes the object as a small point. The receiver of the sensor (photodiode line) detects the position of this point. The angle of incidence changes according to the distance, and thereby the position of the laser point on the receiver. 10. How accurate are laser distance sensors?Compared to other types of laser sensors, OM70 sensors feature one of the thinnest beam shapes, helping to ensure a more precise measuring focus. For example, most point-type lasers typically only go down to 0.2mm x 0.75mm whereas the OM70 goes down to 0.05mm x 0.05mm. 

SummaryChristmas is coming,as well as the New Year's Day. In keeping with the festive lighting of the holiday season,there are various LED lighting architecture in the world. Now let me take you to tour the landmarks lit with LEDs.  In the touring of this LED architecture, I will also introduce how this landmarks be done. Well,these These attention grabbing displays are dependent on products that can deliver a wide range of colors, and a control scheme that allows lighting designers to fully realize their creative ideas. First Stationlet's begin with the glorious Miami in Miami,Florida.  Located downtown, the Miami Tower is a 47-story landmark that you may have seen in films and on television. Before conversion to LEDs, it was lit with a total of 382 1,000 W and 400 W metal halide fixtures, with gels (color filters) applied by maintenance crews to change the color effects. Conversion to a combination of LED flood lighting and strip lighting reduced energy, maintenance, and operating costs by over a quarter million dollars annually, and the building fa?ade can now be changed to a virtually limitless combination of colors and patterns with the “push of a button”. Miami Tower and the other landmarks reviewed in this article are illuminated using Philips Color Kinetics products, which currently have a bit of a monopoly in architectural installations. The control scheme uses a data enabler to combine power with a proprietary Ethernet DMX-based data signal called KiNET, prior to routing to luminaires, junction boxes, and/or strings of strip lights.Over 16 million color combinations can be achieved through the 8-bit channels of Red/Green/Blue/White or Red/Green/Blue/Amber luminaires. A number of different controllers can be used to program either static or dynamic displays. DSP techniques ensure that data corruption is negligible even in noisy, high-EMI environments, e.g., adjacent to powered radio antennas.  Second StationLet's travel across the country to the San Francisco-Oakland Bay Bridge.  The Bay Lights of the San Francisco-Oakland Bay Bridge, installed in 2013 in what was meant to be a two-year run to celebrate the bridge’s 75th anniversary, is currently the largest LED lighting sculpture in the world. With over 25,000 white LED nodes installed on the 1.8 mile western span, the bridge surpasses even the Eiffel Tower in number of LEDs.This lighting system uses light strands,each made up of 50 individually controllable nodes designed to operate in the demanding environment conditons of the bridge--rain,vibration,wind and even road debris. Control software scans the installation to ensure that all lighting is operational Bridge lighting projects are the most challenging to implement according to Philips, because the process can include not just lighting designers, architects, and contractors, but also transportation authorities and the Coast Guard, each with separate concerns and requirements. In addition, lighting installation usually requires workers to hang from suspended cables, and to work at night to minimize traffic impact. Doesn't that sound like fun?  Third StationThis is the season to be shopping,so let's envy the lucky folks in Philadelphia who get to spend time at the appropriately named Lit Brothers Building.  Listed on the National Registry of Historic Places in 1979, the Lit Brothers Building takes up a full city block with its mix of retail and office space. Unlike newer installations, preservation of the historic and structural aspects of the building were paramount in the lighting design, which includes both flood lights and light strips to illuminate the fa-ade and ornamental columns.As engineers, we’re interested in the technical and practical details of these LED projects, like lower operating costs and reduced maintenance requirements, but the non-energy benefits these projects bring can be even more significant. They play a tremendous role in creating a space that local residents and tourists look forward to visiting, enhancing the sense of fun and excitement in the community and the economic boost that often goes with it. Fina Station   The Bai Chay Bridge stands 50 m (164 ft) over Ha Long Bay, one of the most popular and beautiful tourist sites in Vietnam. In 2000, Ha Long Bay was nominated as one of the new seven natural wonders of the world, and in 2004, Ha Long Bay hosted almost 3 million tourists due to its geological value and natural beauty. Scattered across this bay are 1,969 islands, beautiful emerald waters, and with the Bai Chay Bridge, an edition in 2006, a new landmark in Vietnam.The Bai Chay Bridge has the widest width of any cable-stayed, single-plane concrete bridge in the world. The bridge was built to improve traffic conditions and adopt Japanese construction technologies. To make this landmark even more beautiful, the Bai Chay Bridge is now illuminated in colorful LED lights that reflect off the bay waters at night.LED lights were chosen due to their dynamic capabilities, long useful life and energy efficiency. In order to achieve all the goals the investor had set, Philips supplied an environmentally-friendly LED lighting solution for its high efficiency and dynamic and elegant lighting effects.The designers installed ColorReach Powercore gen2 and ColorReach Compact Powercore from Philips Color Kinetics to illuminate the cables and pillars that run high above the bridge, as well as to highlight the dramatic beauty of the bridge’s architecture. ColorGraze MX4 Powercore was used to illuminate the bottom of the bridge, and Archipoint iColor Powercore was used in a direct view application along the spans of the bridge. ConclusionSuch beautiful LED lighting architectures around the world create beauty, enhance entertainment and transform public spaces  for human being and nature. What's more,they witness the LED light's development and become an important milestone in the history of LED lighting. 

SummaryA metamaterial developed by researchers at King's College London uses quantum effects to turn electrons flowing through a circuit into "hot electrons" and light in a highly controlled manner.According to the team,this has potential application in optoelectronics and sensing. BodyThe nanomaterial takes advantage of electron tunnelling to produce streams of particles which can have important applications, when properly controlled.   Accodring to the researcher Dr Pan Wang,this one tiny device offers several amazing applications: plasmon excitation, light generation and chemical reaction activation. And all this is achieved by a small, easy to produce material which only requires a small voltage to function. A voltage applied across the device causes electrons to flow from one material (eutectic gallium indium) to another (gold nanorods). These are separated by an air gap, which would usually stop the electron flow, but because the air gap is less than 1nm, the electrons can ‘tunnel’ through.Most of the tunnelling electrons arrive at the gold nanorod tips in the form of ‘hot electrons’, but a small proportion excite plasmons in the metamaterial to emit light whose wavelength is directly related to the applied voltage. According to the team, this conversion is usually inefficient, but the use of array gold nanorods provides 100billion tunnel junctions, improving electron-to-plasmon conversion and making the emitted light visible. While there are applications in sensing, the researchers point to a benefit in small scale electronics. Since light is generated by applying a voltage along a 10nm thick nanorod, it can be used to transmit information optically between or within chips. The metamaterial allows optical signals to be produced within a much smaller device, holding the potential of faster electronics. "We expected to generate some weak light which we thought should be enough for various nanophotonic applications when we began these studies," added King’s College Professor Anatoly Zayats ,"but But as sometimes happens in the research, the applications are much richer.”