LED Lighting

The LED of the LED light source is made of III-IV compounds, such as GaAs (GaAs), GaP (Gallium Phosphide), GaAsP (GaAsP) and other semiconductors. The core is a PN junction. Therefore, it has the I-V characteristics of a normal P-N junction, that is, forward conduction, reverse cut-off, and breakdown characteristics. In addition, under certain conditions, it also has light-emitting characteristics. Under forward voltage, electrons are injected into the P region from the N region, and holes are injected into the N region from the P region. A part of minority carriers (minority) entering the opposite region is combined with the majority carriers (multipleness) to emit light. Assuming that the light emission occurs in the P region, the injected electrons directly recombine with the valence band holes to emit light, or are first captured by the light-emitting center and then recombine with the holes. In addition to this luminescence recombination, some electrons are captured by the non-luminous center (this center is near the middle of the conduction band and the median band), and then recombined with the hole. The energy released each time is not large enough to form visible light. The greater the ratio of the amount of light-emitting recombination to the amount of non-light-emitting recombination, the higher the light quantum efficiency. Because recombination emits light in the minority carrier diffusion region, light is generated only within a few μm of the PN junction surface.
The theory and practice prove that the peak wavelength λ of light is related to the band gap Eg of the semiconductor material in the light-emitting region, that is, λ≈1240 / Eg (mm)
The unit of Eg in the formula is electron volt (eV). If visible light (violet light at 380nm to 780nm red light) can be generated, the Eg of the semiconductor material should be between 3.26 and 1.63eV. Light having a longer wavelength than red light is infrared light. There are infrared, red, yellow, green, and blue light-emitting diodes, but blue-light diodes are expensive and expensive, and are not widely used.

Limit parameter
(1) Allowable power consumption Pm: The maximum value of the product of the forward DC voltage across the LED and the current flowing through it. Beyond this value, the LED heats up and is damaged.
(2) Maximum forward DC current IFm: The maximum forward DC current allowed. Exceeding this value can damage the diode.
(3) Maximum reverse voltage VRm: the maximum reverse voltage allowed. Beyond this value, the LED may be damaged by breakdown.
(4) Working environment topm: The ambient temperature range in which the light-emitting diode can work normally. Below or above this temperature range, the light emitting diode will not work properly, and the efficiency will be greatly reduced.
Without changing the material, within the limit of the LED, the means to increase the brightness is to increase the current. As the current increases, the heat generated by the LED will increase sharply. Friends who have used LED light source portable projectors, or friends who have micro-projectors, will definitely appreciate that LED light source projectors are very hot and generally have obvious noise. For these products, the small body is one aspect, and the key is that their own heat is caused.
With the increase of power, the heat dissipation problem of LEDs becomes more and more prominent. A large number of practical applications show that the basic reason why LEDs cannot increase input power is because LEDs emit a lot of heat during the work process, which makes the die junction temperature quickly. As the temperature rises, the thermal resistance becomes larger. The higher the input power, the greater the heating effect. The increase of temperature will lead to changes and attenuation of device performance, increase of non-radiative recombination, increase of device leakage current, increase of semiconductor material defects, electromigration of metal electrodes, yellowing of epoxy resin for packaging, etc., which will seriously affect the photoelectric parameters of LEDs. Even power LEDs are disabled. Therefore, for LED devices, it is increasingly important to reduce thermal resistance and junction temperature, and to study the thermal characteristics of light emitting diodes.

Unique advantages
(1) Energy saving: The spectrum of LEDs is almost entirely concentrated in the visible light band, and its luminous efficiency can reach 80-90%. The author also made a comparison between LED lamps and ordinary incandescent lamps, spiral energy-saving lamps and T5 three-color fluorescent lamps. The results show that the ordinary incandescent lamps have a light efficiency of 12lm / w and a lifetime of less than 2000 hours. The light efficiency of spiral energy-saving lamps is 60lm / w, life is less than 8000 hours, T5 fluorescent lamp is 96Alm / w, life is about 10000 hours, and white LED with 5mm diameter is 20-28lm / w, life can be more than 100,000 hours. Some people also predict that the upper limit of future LED life will be infinite.
Everyone thinks that energy saving lamps can save 4/5 energy is a great initiative, but LEDs also save 1/4 energy than energy saving lamps. This is a greater reform of solid light sources. In addition, LED also has other advantages, high light quality, basically no radiation, is a typical green lighting source; reliable and durable, extremely low maintenance costs and so on. Because LED has the characteristics that other solid light sources cannot match, 10 years later LED will be the mainstream light source in the lighting industry.
(2) Safety and environmental protection: The working voltage of LED is low, mostly 1.4-3V; the working current of ordinary LED is only 10mA, and the ultra-high brightness is only 1A. In the production process of LED, do not add “mercury”, do not need inflation, do not need glass shell, good impact resistance, good shock resistance, not easy to break, easy to transport, very environmentally friendly, called “green energy”.
(3) Long service life: The LED is small in size and light in weight, and the shell is encapsulated by epoxy resin, which can not only protect the internal chip, but also has the ability to condense light. The service life of LED is generally between 50,000 and 100,000 hours. Because LED is a semiconductor device, even frequent switching will not affect the service life. At present, incandescent, fluorescent and energy-saving fluorescent lamps are mainly used in home lighting.
(4) Fast response speed: The response frequency of the LED fτ is related to the lifetime τmc of the injected minority carriers. For LEDs made of GaAs materials, whose τmc is generally in the range of 1-10ns, the response frequency is about 16- 160MHz, such a high response frequency is sufficient for displaying a 6.5MHz video signal, which is also one of the key factors to achieve a large screen of video LED.
The lowest response time of LEDs has reached 1 microsecond, and generally it is several milliseconds, which is about 1/100 of the response time of ordinary light sources. Therefore, it can be used in many high-frequency environments, such as car brake lights or status lights, which can shorten the braking time of vehicles behind the vehicle, thereby improving safety.
(5) High luminous efficiency: the light efficiency of incandescent and halogen lamps is 12-24lm / w (lumens / watt), the light efficiency of fluorescent lamps is 50-70lm / w, and the light efficiency of sodium lamps is 90-140lm / w. Most of the power consumption becomes heat loss. The improved light efficiency of LED can reach 50-200lm / w, and the light has good monochromaticity and narrow spectrum. It can directly emit colored visible light without filtering.
(6) The small size of LED components: it is more convenient for the arrangement and design of various equipment, and it can better achieve the effect of “seeing only the light but not the light source” in night lighting.
(7) LED light energy concentration is high: concentrated in a small wavelength window, high purity.
(8) Strong directivity of LED light emission: The brightness attenuation is much lower than that of traditional light sources.
(9) LED low-voltage direct current can be driven: it has the advantages of small load and weak interference, and has lower requirements on the use environment.
(10) The composition of the luminescence spectrum can be well controlled: it can be well used for local or accent lighting in museums and exhibition halls.
(11) It is possible to control the size of the semiconductor light-emitting layer and the prohibited band width of the semiconductor material: thereby emitting light of various colors, and the chroma is higher.
(12) High color rendering: will not cause harm to human eyes.

Application area
Among LED lighting fixtures, decorative lights such as bottom lights, chandeliers, and projection lights, and LED lighting fixtures for reflective purposes can be completely competent for any occasion, including art
LED control module
Museums and other places with high color requirements. However, for large-scale facilities such as shopping malls and office buildings, although large-scale lighting LED lamps have been born, their directivity (the light emitted by LED chips is straight and the divergence is not good) is too high, resulting in an average design in a large area The illumination is difficult. The tube-type LED lighting fixtures are too densely arranged, the design cost is too high, and the energy saving effect is lost. Therefore, at this stage of decorative use occasions, LED lighting fixtures are fully available, and large-area indoor lighting is still immature.
1) Signal indication application: Signal lighting is an area where LED monochromatic light is widely used and is relatively early, accounting for about 4% of the LED application market.
2) Display applications: signs, billboards, large-screen displays, etc. LED applications for display screens account for about 20% -25% of LED applications, and display screens can be divided into monochrome and color.
3) Lighting application:

Yi portable lamps: flashlights, headlights, miner lights, diving lights, etc .;

LED Lighting Flashlight
Automotive lights: high-level brake lights, brake lights, turn lights, reversing lights, etc., high-power LEDs have been widely used in automotive lighting.
Special lighting: solar garden lights, solar street lights, underwater lights, etc .; Due to the small size of the LED, which is convenient for dynamic brightness and color control, it is more suitable for architectural lighting.
Backlighting: LED display backlights for general electronic devices, notebook computer backlights, large-sized and oversized LCD monitor backlights, etc. LEDs are the most widely used LED backlights for mobile phone displays.
Projection light source: RGB light source for projector.
General lighting: various general lighting fixtures, lighting sources, etc. are divided into commercial lighting and home lighting.