Briefly describe the principle of LED illumination
LED lighting principle:
A light-emitting diode is a device that emits light in a forward direction to a semiconductor p-n junction, usually using a double heterojunction and a quantum well structure. In 1962, GE (General Electric) commercialized red LEDs for the first time with GaAsP. The initial red LED has a luminous flux of 0.1 lm/W, which is about 1/150 of that of ordinary light, and its luminous efficiency is increased by about an order of magnitude every 10 years. Recently, blue and green LEDs have been put into practical use, and their luminous intensity exceeds that of AlGaAs-based red LEDs.
This LED uses a quantum semiconductor structure in which a nitride semiconductor (InGaN mixed crystal) is used as an active (light-emitting) layer, and its luminous intensity exceeds 10 cd, and the quantum efficiency exceeds 20%. In addition, AIInGaP red LEDs (630 nm) and amber-LEDs (595 nm) with external quantum efficiencies exceeding 50% have also been developed. The quantum efficiency of the InGaN green and blue LEDs is also close to the above values.led bulb light
Candela (cd) is a unit of luminous intensity used to indicate the intensity of visible light LED illumination. The luminous intensity I can be expressed by the luminous flux Φ and the solid angle Ω. I=dΦ/dΩ[cd]Φ=Km∫V(λ)Pλdλ[lm] where Km is the maximum visibility (683 nm) in the wavelength range of 555 nm, and green is the brightest for the human eye. V(λ) is the relative visibility [V(555nm)=1] at a wavelength of λ, and Pλ is the spectral radiant flux.
White LED lighting principle:
It is a new type of LED consisting of InGaN blue LEDs and phosphors. The phosphor is coated on the blue LED chip, and finally the periphery of the chip is sealed with epoxy. Two ways (single-chip type and multi-chip type) provide white light with good color tone (Ra 85). One is to illuminate red, green, blue (R.G.B) or cyan and yellow-orange two or three kinds of LEDs at the same time; the other is to use a radiation blue or ultraviolet LED as an excitation source to excite the phosphor. The first method is not only defective in the driving voltage or the light-emitting output of the LED, but also has problems in temperature characteristics or device life, and thus there is still a distance from the practical use. The second way is to use a device, drive circuit, easy to design.
White LEDs have three incentives:
1. Use a blue LED to excite a yellow-emitting phosphor. This white light structure is to put the blue LED and the YAG fluorescent material together, and to excite the fluorescent material with blue light, so that the spectrum emitted by it is white light. In this regard, Nichia Corporation has a worldwide patent.led flood light
2. Excitation of the R.G.B phosphor with an ultraviolet LED. The white LED illumination source that excites the phosphor can be widely used in illumination because the phosphor group can emit light of various colors other than white light. White LEDs have been developed with R.G.B trichromatic LEDs. The current laboratory-level luminous efficiency has exceeded 50 lm/W, which is expected to exceed 100 lm/W in recent years, while the best luminous efficiency of the red portion has exceeded 100 lm/W.led flame bulb
3. Use three kinds of red, green and blue light-emitting diodes to adjust their individual brightness to achieve white light. Generally, the red, green and blue brightness ratio should be 3:6:1, or only red, green or blue. Two LEDs adjust their individual brightness to emit white light. The biggest disadvantage of such a white light structure is that the cost is high, which is not conducive to commercial development.
Dalian Xinghai Technology Co., Ltd.