Introduction to the illumination mechanism of LED light source

Now with the maturity of the LED industry supply, the entry barrier is low, and a large number of small businesses are flooding, resulting in a surplus of LED industry, and due to the low utilization rate of the company, the market is definitely competitive with the big brands such as Philips and Osram . Osram) and GE, these large manufacturers actively occupy the LED main lighting market through vertical integration or strategic alliance layout. Whether the gross profit margin is exploited by layers or by strong enemies, small factories cannot escape huge market pressure.

China has abundant non-ferrous metal resources, and its gallium and indium reserves are abundant, accounting for 70%-80% of the world's reserves. This makes China's development of the semiconductor lighting industry a resource advantage. By 2010, the output value of the entire Chinese LED industry will exceed 150 billion yuan. In Japan, as early as 2002, it spent 5 billion yen to promote white light, and the budget for the entire plan was 6 billion yen.

With the rapid growth of LED penetration, the price war will come in 2010. Because LED is different from the traditional sales mode of lamps and light sources, under this pressure, some companies cannot balance product quality and price competitiveness. Will fall into the fate of mergers or acquisitions or being eliminated.

On May 7-12, 2010, the Lighting Society of Henan Province organized lighting experts and entrepreneurs to visit Japan's lighting status and found that the current status of LED lighting in Japan is not satisfactory.

In recent years, the most interesting event in the field of lighting is the rise of semiconductor lighting. In the mid-1990s, Nakamura and others of Japan Nichia Corporation broke through the key technologies for manufacturing blue light-emitting diodes (LEDs) through unremitting efforts, and developed a technology that uses fluorescent materials to cover blue LEDs to produce white light sources.

Led is an abbreviation for LightEmittingDiode. Light-emitting diode is a new type of solid-state cold light source. The most remarkable features of LED are long service life, high photoelectric conversion efficiency, good seismic performance and convenient use. It is widely used in lighting systems. At the same illumination, LED lamps have significant advantages in power consumption and lifetime over incandescent and fluorescent lamps.

The development of various white light-emitting methods and the development of a new generation of phosphors have greatly improved the luminous efficiency of LEDs. The current industrial products have been improved from 45lm/w to 100lm/w (to 2009, Cree's cool white light) The effect has exceeded 100lm/W at 350mA, and the warm white light has exceeded 75lm/W). The research level is 160lm/w, and the target maximum level is expected to be above 200lm/w. The life span is 40,000 hours to 80,000 hours.

First, the light-emitting mechanism of LED light source

It is very different from the principle of illumination of incandescent lamps or gas discharge lamps. The spontaneous luminescence of LEDs is due to the recombination of electrons and holes.

The LED is composed of a P layer formed of a P-type semiconductor and an N layer formed of an N-type semiconductor, and an intermediate active layer formed of a double heterostructure. The active layer is a light-emitting region, and an external power source is used 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. When entering the active layer, when the electrons and holes recombine, spontaneous radiation will be generated, as shown in Figure 1. Due to the different materials used, LEDs have different energy levels in the diodes. The height difference of the energy level affects the energy of the combined photons to produce different wavelengths of light, that is, different colors of light, such as Red, orange, yellow, green, blue or invisible light.

Second, white LED

The advent of white LEDs has provided white LED semiconductor lighting for more and more indoor and outdoor lighting projects. The efficacy of white LEDs has made great progress, and white LEDs have even begun to challenge the status of traditional light sources.

At present, there are two main ways to obtain white LEDs: the first is to obtain white light by phosphor conversion; the second is to package LED chips of different colors together, and the multi-chip hybrid emits white light. For the above two approaches, according to the number of primary light sources participating in the mixed white light, they can be further divided into two primary color systems and multiple primary color systems.

Phosphor conversion white LED

(1) Two primary color phosphor conversion white LED

The two-primary white LED is made of a blue LED chip and a YAG phosphor. The commonly used blue light chip is an InGaN chip, and an AlInGaN chip can also be used. The advantages of the blue chip LED with the YAG phosphor method are: simple structure, low cost, relatively simple manufacturing process, but the method also has several disadvantages, such as the high efficiency of the blue LED, resulting in 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 lifetime.

(2) Three primary color phosphor conversion LED

The trichromatic phosphor LED can effectively improve the color rendering of the LED under the premise of higher 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 are effectively excited by UV radiation.

Compared with the method of obtaining white light by the blue LED+YAG phosphor, it is easier to obtain white light of uniform color by the method of ultraviolet LED+three-primary phosphor, because the color of the LED is determined only by the ratio of the phosphor. In addition, this type of white LED has high color rendering, light color and color temperature are adjustable, and high conversion efficiency phosphor can improve the light efficiency of the LED.

However, the method of ultraviolet LED+tricolor phosphor has certain defects, such as the low efficiency of the phosphor in converting ultraviolet radiation; the powder mixing is difficult; the packaging material is easy to aging under ultraviolet light, and the life is short. Moreover, the red and green phosphors with high conversion efficiency are mostly sulfide systems, and such phosphors have poor light-emitting stability and large light decay.