Analysis of main technical routes of white LED for lighting

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Analysis of main technical routes of white LED for lighting

September 22
13:40 2022

1. Blue LED chip+yellow green phosphor, including polychrome phosphor derivative

The yellow green phosphor layer absorbs the blue light of some LED chips to produce photoluminescence, and the blue light from the LED chips transmits out of the phosphor layer and converges with the yellow green light emitted by the phosphor at various points in space, and the red green blue light is mixed to form white light; In this way, the maximum theoretical value of photoluminescence conversion efficiency of phosphor, one of the external quantum efficiency, will not exceed 75%; The highest extraction rate of light from the chip can only reach about 70%. Therefore, theoretically, the maximum luminous efficiency of blue light white LED will not exceed 340 Lm/W, and CREE will reach 303 Lm/W a few years ago. If the test results are accurate, it is worth celebrating.

2. Red green blue three primary color combination RGB LED type, including RGB W LED type, etc

The three light-emitting diodes, R-LED (red)+G-LED (green)+B-LED (blue), are combined to form a white light by directly mixing the red, green and blue light emitted in space. In order to generate high luminous efficiency white light in this way, first of all, all color LEDs, especially green LEDs, must be efficient light sources, which account for about 69% of “equal energy white light”. At present, the light efficiency of blue LED and red LED has been very high, with the internal quantum efficiency exceeding 90% and 95% respectively, but the internal quantum efficiency of green LED is far behind. This phenomenon of low green light efficiency of GaN based LED is called “green light gap”. The main reason is that the green LED has not yet found its own epitaxial material. The efficiency of the existing phosphorus arsenic nitride series materials is very low in the yellow green chromatographic range. However, the green LED is made of red light or blue light epitaxial materials. Under the condition of low current density, because there is no phosphor conversion loss, the green LED has higher luminous efficiency than the blue light+phosphor green light. It is reported that its luminous efficiency reaches 291Lm/W under the current of 1mA. However, under high current, the luminous efficiency of green light caused by Droop effect decreases significantly. When the current density increases, the luminous efficiency decreases