LED is an abbreviation for Light Emitting Diode. LED is a new type of solid-state cold light source. The most prominent feature of LED is its long service life, high photoelectric conversion efficiency, good anti-seismic performance, and easy use. It is widely used in lighting systems. In the same illuminance, the power consumption and life of LED lamps have obvious advantages over incandescent and fluorescent lamps.
The development of various white light emitting methods and the development of a new generation of phosphors have led to a significant increase in the luminous efficiency of LEDs. Currently, industrial products have been increased from 45 to 100 lm/w (in 2009, Cree's cool white light The efficiency has exceeded 100lm/W at 350mA, while the warm white light also exceeds 75lm/W), the research level is 160lm/w, and the target maximum level is expected to be more than 200lm/w. Life from 40,000 hours to 80,000 hours.
China is rich in non-ferrous metal resources, and its reserves of gallium and indium are abundant, accounting for 70%-80% of the world's reserves. This has made China's semiconductor lighting industry a resource advantage. By 2010, the output value of China's LED industry will exceed 150 billion yuan. In Japan, as of early in 2002, it spent 5 billion yen to implement white light lighting, and the overall plan had a budget of 6 billion yen.
From May 7th to 12th, 2010, the lighting experts and entrepreneurs of the Henan Provincial Lighting Institute visited Japan to investigate the status of lighting in Japan and found that the status quo of LED lighting in Japan is not satisfactory.
First, the light emitting mechanism of LED light sources is very different from the light emitting principle of incandescent or gas discharge lamps. The spontaneous luminescence of LEDs is due to the recombination of electrons and holes.
The LED is an N layer formed of a P layer formed of a P-type semiconductor and an N-type semiconductor, and an intermediate active layer formed of a double heterostructure. The active layer is a light emitting region and uses an external power source to inject electrons into the PN junction. Under forward bias, the electrons in the N region will diffuse in the positive direction and enter the active layer, and the holes in the P region will also diffuse in the negative direction. Into the active layer, when the electrons and holes recombine, they will generate spontaneous emission light, as shown in Figure 1. Because of the different materials used by LEDs, the energy levels of electrons and holes in the diodes are also different. The difference in height affects the energy of the photons combined to produce different wavelengths of light, ie different colors of light, such as red, orange, yellow, green, blue, or invisible light.
Second, white LED
The emergence of white LEDs has provided white LED semiconductor lighting for more and more indoor and outdoor lighting projects. White light LEDs have made great strides in light efficiency, and white LEDs have even begun to challenge traditional light sources.
At present, there are mainly two ways to obtain white LEDs: the first is to obtain white light through phosphor conversion; the second is to package LED chips of different colors together, and the multi-chip is mixed to emit white light. For the above two approaches, according to the number of primary color light sources participating in the mixed white light, they can be further divided into two primary color systems and multiple primary color systems.
1 phosphor conversion white LED
(1) Two-color phosphor conversion white LED
Two-primary white LEDs are made using blue LED chips and YAG phosphors. The commonly used blue chips are InGaN chips, and AlInGaN chips may also be used. The advantage of the blue chip LED with YAG phosphor method is that the structure is simple, the cost is low, and the manufacturing process is relatively simple. However, this method also has several disadvantages, such as the low efficiency of the blue LED and the low efficiency of the white LED; the phosphor itself exists. Energy loss; phosphors and packaging materials age over time, resulting in color temperature drift and shortened life.
(2) Trichromatic phosphor conversion LED
Tricolor phosphor LED can effectively improve the color rendering of LED under the condition of high luminous efficiency. The most common way to obtain a trichromatic white LED is to use a UV LED to excite a set of trichromatic phosphors that can be effectively excited by UV radiation.
Compared with the blue LED+YAG phosphor to obtain white light, the use of UV LED+trichromatic phosphors makes it easier to obtain consistent white light because the light color of the LED is only determined by the ratio of the phosphors. In addition, this type of white LED has high color rendering, light color and color temperature can be adjusted, and the use of high conversion efficiency phosphor can improve the light efficiency of the LED.
However, there are certain defects in the methods of UV LED+trichromatic phosphors. For example, phosphors have low efficiency in converting ultraviolet radiation; powder mixing is difficult; and packaging materials are susceptible to aging under ultraviolet light irradiation and have a short lifetime.
The development of various white light emitting methods and the development of a new generation of phosphors have led to a significant increase in the luminous efficiency of LEDs. Currently, industrial products have been increased from 45 to 100 lm/w (in 2009, Cree's cool white light The efficiency has exceeded 100lm/W at 350mA, while the warm white light also exceeds 75lm/W), the research level is 160lm/w, and the target maximum level is expected to be more than 200lm/w. Life from 40,000 hours to 80,000 hours.
China is rich in non-ferrous metal resources, and its reserves of gallium and indium are abundant, accounting for 70%-80% of the world's reserves. This has made China's semiconductor lighting industry a resource advantage. By 2010, the output value of China's LED industry will exceed 150 billion yuan. In Japan, as of early in 2002, it spent 5 billion yen to implement white light lighting, and the overall plan had a budget of 6 billion yen.
From May 7th to 12th, 2010, the lighting experts and entrepreneurs of the Henan Provincial Lighting Institute visited Japan to investigate the status of lighting in Japan and found that the status quo of LED lighting in Japan is not satisfactory.
First, the light emitting mechanism of LED light sources is very different from the light emitting principle of incandescent or gas discharge lamps. The spontaneous luminescence of LEDs is due to the recombination of electrons and holes.
The LED is an N layer formed of a P layer formed of a P-type semiconductor and an N-type semiconductor, and an intermediate active layer formed of a double heterostructure. The active layer is a light emitting region and uses an external power source to inject electrons into the PN junction. Under forward bias, the electrons in the N region will diffuse in the positive direction and enter the active layer, and the holes in the P region will also diffuse in the negative direction. Into the active layer, when the electrons and holes recombine, they will generate spontaneous emission light, as shown in Figure 1. Because of the different materials used by LEDs, the energy levels of electrons and holes in the diodes are also different. The difference in height affects the energy of the photons combined to produce different wavelengths of light, ie different colors of light, such as red, orange, yellow, green, blue, or invisible light.
Second, white LED
The emergence of white LEDs has provided white LED semiconductor lighting for more and more indoor and outdoor lighting projects. White light LEDs have made great strides in light efficiency, and white LEDs have even begun to challenge traditional light sources.
At present, there are mainly two ways to obtain white LEDs: the first is to obtain white light through phosphor conversion; the second is to package LED chips of different colors together, and the multi-chip is mixed to emit white light. For the above two approaches, according to the number of primary color light sources participating in the mixed white light, they can be further divided into two primary color systems and multiple primary color systems.
1 phosphor conversion white LED
(1) Two-color phosphor conversion white LED
Two-primary white LEDs are made using blue LED chips and YAG phosphors. The commonly used blue chips are InGaN chips, and AlInGaN chips may also be used. The advantage of the blue chip LED with YAG phosphor method is that the structure is simple, the cost is low, and the manufacturing process is relatively simple. However, this method also has several disadvantages, such as the low efficiency of the blue LED and the low efficiency of the white LED; the phosphor itself exists. Energy loss; phosphors and packaging materials age over time, resulting in color temperature drift and shortened life.
(2) Trichromatic phosphor conversion LED
Tricolor phosphor LED can effectively improve the color rendering of LED under the condition of high luminous efficiency. The most common way to obtain a trichromatic white LED is to use a UV LED to excite a set of trichromatic phosphors that can be effectively excited by UV radiation.
Compared with the blue LED+YAG phosphor to obtain white light, the use of UV LED+trichromatic phosphors makes it easier to obtain consistent white light because the light color of the LED is only determined by the ratio of the phosphors. In addition, this type of white LED has high color rendering, light color and color temperature can be adjusted, and the use of high conversion efficiency phosphor can improve the light efficiency of the LED.
However, there are certain defects in the methods of UV LED+trichromatic phosphors. For example, phosphors have low efficiency in converting ultraviolet radiation; powder mixing is difficult; and packaging materials are susceptible to aging under ultraviolet light irradiation and have a short lifetime.
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