1. Blue-LED chip + yellow-green phosphor type including multi-color phosphor derivative type

 The yellow-green phosphor layer absorbs part of the blue light of the LED chip to produce photoluminescence, and the other part of the blue light from the LED chip is transmitted out of the phosphor layer and merges with the yellow-green light emitted by the phosphor at various points in the space, and the red, green and blue light is mixed to form white light; In this way, the highest theoretical value of phosphor photoluminescence conversion efficiency, which is one of the external quantum efficiency, will not exceed 75%; and the highest light extraction rate from the chip can only reach about 70%, so in theory, blue white light The highest LED luminous efficiency will not exceed 340 Lm/W, and the CREE reached 303Lm/W in the past few years. If the test results are accurate, it is worth celebrating.

2. The combination of red, green and blue RGB LED type includes RGBW-LED type, etc.

 The three light-emitting diodes of R-LED (red) + G-LED (green) + B- LED (blue) are combined together, and the three primary colors of red, green and blue are directly mixed in space to form white light. In order to produce high-efficiency white light in this way, firstly, LEDs of various colors, especially green LEDs, must be high-efficiency light sources, which can be seen from the “equal energy white light” in which green light accounts for about 69%. At present, the luminous efficiency of blue and red LEDs has been very high, with internal quantum efficiencies exceeding 90% and 95%, respectively, but the internal quantum efficiency of green LEDs is far behind. This phenomenon of low green light efficiency of GaN-based LEDs is called the “green light gap.” The main reason is that green LEDs have not found their own epitaxial materials. Existing phosphorous arsenic nitride series materials have low efficiency in the yellow-green spectrum. Red or blue epitaxial materials are used to make green LEDs. Under the condition of lower current density, because there is no phosphor conversion loss, green LED has higher luminous efficiency than blue + phosphor type green light. It is reported that its luminous efficiency reaches 291Lm/W under the condition of 1mA current. However, the drop in the light efficiency of the green light caused by the Droop effect under a larger current is significant. When the current density increases, the light efficiency drops quickly. At a current of 350mA, the light efficiency is 108Lm/W. Under the condition of 1A, the light efficiency drops. To 66Lm/W.

For III phosphines, the emission of light to the green band has become a fundamental obstacle to the material system. Changing the composition of AlInGaP to make it emit green light instead of red, orange or yellow—causing insufficient carrier limitation is due to the relatively low energy gap of the material system, which excludes effective radiation recombination.

Therefore, the way to improve the light efficiency of green LEDs: on the one hand, study how to reduce the Droop effect under the conditions of existing epitaxial materials to improve light efficiency; on the second, use the photoluminescence conversion of blue LEDs and green phosphors to emit green light. This method can obtain high luminous efficiency green light, which can theoretically achieve higher luminous efficiency than the current white light. It belongs to non-spontaneous green light. There is no problem with lighting. The green light effect obtained by this method may be greater than 340 Lm/W, but it will still not exceed 340 Lm/W after combining white light; third, continue to research and find your own epitaxial material, only In this way, there is a glimmer of hope that after obtaining green light that is much higher than 340 Lm/w, the white light combined by the three primary colors of red, green and blue LEDs may be higher than the luminous efficiency limit of blue chip white LEDs of 340 Lm/ W.

3. Ultraviolet LED chip + three primary color phosphors emit light 

The main inherent defect of the above two types of white LEDs is the uneven spatial distribution of luminosity and chromaticity. The ultraviolet light is not perceivable by the human eye. Therefore, after the ultraviolet light exits the chip, it is absorbed by the three primary color phosphors of the encapsulation layer, converted into white light by the photoluminescence of the phosphor, and then emitted into the space. This is its biggest advantage, just like traditional fluorescent lamps, it has no spatial color unevenness. However, the theoretical luminous efficiency of the ultraviolet chip-type white light LED cannot be higher than the theoretical value of the blue chip-type white light, let alone the theoretical value of the RGB-type white light. However, only through the development of high-efficiency three-primary phosphors suitable for ultraviolet light excitation can it be possible to obtain ultraviolet white light LEDs that are close to or even higher than the above two white light LEDs at this stage. The closer to the blue ultraviolet light LED, the possibility The larger the white light LED of medium wave and short wave ultraviolet type is impossible.