White light is a combination of light, white LED can be divided into single chip, dual chip and three chips, etc., the following will be introduced according to this classification, will also introduce some technical indicators of white LED for lighting.
White LED lighting principle
Single chip
InGaN (blue) / YAG phosphor
This is a relatively mature product, including 1W and 5W Lumileds. These products use a flip-chip structure to improve luminous efficiency and heat dissipation. Improvements in the phosphor coating process can increase color uniformity by a factor of 10. Experiments have shown that the increase in current and temperature causes the LED spectrum to be somewhat blue-shifted and red-shifted, but has little effect on the fluorescence spectrum. The life test results are also good. After 12,000 hours of operation, the light output of Φ5 white LED is reduced by 80%. This power LED only drops 10% after 12,000 hours of operation, and it is estimated that it will drop by 30% after 50,000 hours. . The power LED called Luxeon has a maximum efficiency of 44.3 lm/w, a maximum luminous flux of 187 lm, an industrial product of 120 lm and a Ra of 75-80.
InGaN (blue) / red phosphor + green phosphor
Lumileds uses 460nm LEDs with SrGa2S4:Eu2+ (green) and SrS:Eu2+ (red) phosphors. The color temperature can reach 3000K-6000K, and Ra reaches 82-87, which is better than the above products.
InGaN (ultraviolet) / (red + green + blue) phosphor
Cree, Nichia, Toyota and other companies are vigorously developing UV LEDs. Cree has produced 50mW, 385nm-405nm UV LEDs; Toyota has produced such white LEDs with Ra greater than or equal to 90, but the luminous efficiency is not ideal; Nichia has recently produced 365nm, 1mm2, 4.6V, 500mA High-power UV LEDs, such as white LEDs, will have better results.
ZnSe and OLED white light devices have also made progress, but they are far from industrial production.
Dual chip
It can be made of blue LED+yellow LED, blue LED+yellow green LED and blue-green LED+yellow LED. This kind of device is cheaper, but because it is white light formed by two color LEDs, the color rendering is poor, only in color rendering. Use in places where the requirements are not high.
Three chip (blue + green + red) LED
Philips uses 470nm, 540nm and 610nm LED chips to make devices with Ra greater than 80, with color temperatures up to 3500K. If LED chips of 470nm, 525nm and 635nm are used, the yellow tone is lacking, and Ra can only reach 20 or 30.
Wavelength compensation and luminous flux feedback methods are used to reduce color shift to an acceptable level. American TIR company uses Luxeon RGB devices to make system products for landscape lighting, and Lumileds made LCD TV screens (22 inches), and the performance of the products is good.
Four chips (blue + green + red + yellow) LED
White LEDs with Ra greater than 90 can be fabricated using 465 nm, 535 nm, 590 nm, and 625 nm LED chips.
In addition, Norlux uses 90 tri-color chips (R, G, B) to make 10W white LEDs, each with a luminous flux of 130lm and a color temperature of 5500K.
White LED technical indicators
The white LED for lighting is different from the traditional LED products . There are some special requirements on the technical performance indicators: the luminous flux of a Φ5 LED is only about 1 lm, and the white light power LED used for illumination is expected to reach 1 Klm. Of course, power LEDs with luminous fluxes of 0.1Klm and 0.01Klm can also meet the lower lighting requirements. Since the 15W incandescent lamp is less efficient, only 8lm/w, the luminous flux of a 15W incandescent lamp is comparable to that of a 25lm/w white light LED5W device.
Luminous efficiency The current industrialized products have been increased from 15 lm / w to 100 lm / w, the research level is 125 lm / w, the highest level has reached 130 lm / w.
The color temperature is between 2500K and 10000K, preferably between 2500K and 5000K.
The color rendering index Ra is preferably 100. Currently available to 85
Both the stability wavelength and the luminous flux are required to be stable, but the degree of stability depends on the needs of the occasion.
Life expectancy is 50,000 hours to 100,000 hours. (Edit: Technology)
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