What is the principle of white LED illumination by fluorescence conversion?

Last Update Time: 2019-01-11 10:25:12

From the perspective of chromaticity theory, white light is composed of seven monochromatic light (red, orange, yellow, green, blue, purple). There are three ways to realize white light LED: Phaophor Cowered LED (PC-LED), multi-chip combination and multi-quantum well composite.


The fluorescence conversion method is that when the low voltage DC current is switched on, the light-emitting material fluorescent powder coated on the diode chip can obtain white light. At present, there are two kinds of white LED fabricated by fluorescence conversion according to the type of luminescent semiconductor chip:


(1)Blue LED chip type white light LED.

At present, the white light can be obtained by adjusting the intensity ratio of blue light and yellow light, which is mainly composed of blue light emitted by LED chip and yellow phosphor emitted by yellow phosphor which can be excited by blue light.


The commercially mature white LED packaging technology is made on the basis of yellow phosphors coated with yttrium aluminum garnet on blue LED chips. 

the phosphor is structured in two ways: the phosphor is directly in contact with the blue-ray LED chip and the film-coated phosphor is coated on the blue-light LED chip in two ways. The advantages of this method are simple manufacturing, low technology cost, high production efficiency, stable color and strong practicability, but there are some obvious shortcomings:

1) the complex white light mode of blue and yellow light. The spectrum of white light is due to the lack of red light in the spectrum.

The color index of white light is lower than that of Ra 85).


2)In the process ofLED packaging, the quality of glue is difficult to control, which leads to poor uniformity of light emitted by LED and incongruity of hue, so that the angle between the directional light of LED and the scattered light of phosphor is not consistent, and there is a blue background.


3)The white light properties (such as color temperature) of  LED are greatly affected by the operating current of blue LED chip, the coating thickness of phosphor, the working temperature of phosphor, the aging of phosphor, etc., which will make the white light output of LED unstable and uneven.



(2) Ultraviolet LED chip type white light LED.

This type of white LED is made by coating the tricolor phosphor on the (near) ultraviolet LED chip. It is not easy to feel in the (near) ultraviolet light human vision, its excited RGB phosphors mix to produce white light, because the light emitted by the chip does not participate in the ratio of white light, compared with the blue light LED chip type white light LED, It has many advantages: the display index is high and Ra value is close to 90, the white light quality can be easily adjusted according to the proportion of RCB, the color is stable (the luminous color is almost independent of the chip current wave),good color reducibility, rich phosphor materials, etc.


Its disadvantages are: high power ultraviolet (near ultraviolet) LED chip is difficult to manufacture, ultraviolet (near ultraviolet) energy is high, because of the existence of Slocks, there is energy loss in the excitation process, and the luminous efficiency is not high. The epoxy resin will decompose and aging under ultraviolet light irradiation for a long time, which will reduce the transmittance and shorten the service life. It is difficult to achieve uniform mixing of three primary color phosphors.In the event that the leak endangers human health.


If you want to know more, our website has product specifications for the LEDs, you can go to Allicdata Electronics Limited to get more information.



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