LED (light emitting diode) lighting is equal to light emitting diode (LED) illumination. It USES solid semiconductor chip as luminescent material. In the semiconductor, excess energy is released through carrier recombination, which causes photon emission and directly emits red, yellow, blue and green light. On this basis, fluorescent powder can be added based on the principle of three primary colors to emit light of any color. Using LED as a light source to produce lighting appliances is LED lamps. LED lighting lamps, reflective use of LED lighting lamps can be fully qualified for any occasion, large area of indoor lighting is not mature.
LED light source, LED by Ⅲ - Ⅳ compounds, such as GaAs (gallium arsenide), GaP (gallium phosphide), GaAsP phosphorus (GaAs) made of semiconductor, such as its core is the p-n junction. Therefore, it has the i-v characteristics of the general p-n junction, that is, positive guide pass, reverse cut-off and breakdown characteristics. In addition, under certain conditions, it also has the characteristic of luminescence. At forward voltage, electrons are injected into P region from N region and holes into N region from P region. Some of the minority carriers (minority carriers) entering the opposite region compound with most carriers (multiple carriers) to glow.
Assuming that the luminescence occurs in the p-region, then the injected electron is directly combined with the valence band hole to emit light, or it is captured by the luminescence center and then combined with the hole to emit light. In addition to this luminous recombination, some electrons are captured by the non-luminous center (which lies between the conduction band and the dielectric band), and then recombined with the hole, each time releasing little energy to form visible light. The higher the ratio of luminescent recombination to non-luminescent recombination, the higher the quantum efficiency. Because the recombination is luminescent in the region of few - particle diffusion, the light is produced only within micron near the PN junction.
Theoretical and practical evidence suggests that the peak wavelength of light is dependent on bandgap Eg, or lambda ≈1240/Eg (mm).
Where, the unit of Eg is electron volts (eV). If visible light can be generated (wavelength of 380nm violet light ~ 780nm red light), the semiconductor material Eg should be between 3.26 and 1.63eV. Wavelengths longer than red light are infrared light. There are infrared, red, yellow, green and blue light emitting diodes, but the cost and price of blue light diodes are very high.
Green environmental protection
It does not contain mercury, lead and other heavy metals that cause a lot of environmental pollution. When it emits light, it will not produce ultraviolet rays. Therefore, LED lighting will not be as clean and tidy as traditional lamps with many mosquitoes surrounding the light source. The innovative design of constant current drive of metal shell enables the product to convert electrical energy into light with very high efficiency.
(I) energy saving: the LED spectrum is almost entirely concentrated in the visible spectrum, and its luminous efficiency can reach 80-90%. The author will also LED lights with ordinary incandescent lamp, spiral energy-saving lamps T5 trichromatic fluorescent lamps and done some comparison, the result shows: the ordinary incandescent light efficiency of 12 lm/w, life is less than 2000 hours, spiral energy-saving lamp luminous efficacy of 60 lm/w, life is less than 8000 hours, T5 fluorescent lamp is 96 alm/w, life is about 10000 hours, and a diameter of 5 mm white LED to 20-28 lm/w, life can be greater than 100000 hours. Some predict an infinite lifetime of leds in the future.
Most people think that energy-saving lamps can save up to 4/5 energy, which is a great innovation, but leds can save up to 1/4 more energy than energy-saving lamps, which is a great innovation of solid light source. In addition, LED also has other advantages. It is a typical green lighting source with high light quality and basically no radiation. Reliable and durable, extremely low maintenance, etc. Because of the characteristics of LED, which cannot be matched by other solid light sources, LED will be the mainstream light source in the lighting industry in 10 years.
(ii) safety and environmental protection: the working voltage of LED is low, mostly 1.4 -- 3V; Ordinary LED operating current is only 10mA, ultra-bright but also 1A. LED in the production process do not add "mercury", do not need to inflate, do not need a glass shell, good impact resistance, good shock resistance, not easy to break, easy to transport, very environmental protection, known as "green energy".
(3) long service life: LED is small in size and light in weight, and the enclosure is epoxy resin. It can not only protect the internal chip, but also has the ability of light transmission and concentration. LED service life is generally between 50,000 and 100,000 hours, because LED is a semiconductor device, even the frequent switch, will not affect the service life. What current household illume basically USES is incandescent lamp, fluorescent lamp and energy-saving fluorescent lamp.
(4) fast response: LED the response frequency f tau and minority carrier injection of tau MC about life, such as GaAs material made of LED, the tau MC generally range between 1-10 ns, the frequency response of about 16-160 MHz, such a high response frequency for video signal display 6.5 MHz is enough, this is one of the key factors to realize video LED large screen.
LED response time has been as low as 1 microsecond, generally several milliseconds, about 1/100 of the response time of ordinary light source. 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 car, thus improving safety.
High luminous efficiency: the luminous efficiency of incandescent lamp and halogen tungsten lamp is 12-24lm/w(lumen/watt), the luminous efficiency of fluorescent lamp is 50-70lm /w, and the luminous efficiency of sodium lamp is 90-140lm /w. And LED light efficiency can reach 50-200lm /w, and the light monochromatism is good, the spectrum is narrow, can directly emit colored visible light without filtering.
(6) small size of LED components: it is more convenient for the layout and design of various equipment, and can better achieve the effect of "only the light can not see the light source" in night lighting.
(7)LED light energy concentration: concentrated in a small wavelength window, high purity.
(8)LED luminous directivity is strong: the brightness attenuation is much lower than the traditional light source.
(9)LED low-voltage direct current drive: with the advantages of small load, weak interference, low requirements for the use of the environment.
(10) .good control of luminescence spectrum composition: thus it can be used for local or focal lighting in museums and exhibition halls.
11) the size of forbidden band amplitude of semiconductor luminescent layer and semiconductor material can be controlled so as to emit various colors of light with higher chromaticity.
(12) high color rendering: no harm to people's eyes.