1, LED luminescence of the structure and principles
50 years ago, people have to understand semiconductor materials can produce light of the basic knowledge, the first commercial diodes in 1960. English is the LED light emitting diode (LED) acronym, and its basic structure is an electroluminescent semiconductor materials, placed in a wire rack, then sealed with epoxy resin around, played within the core protection The role of line, so the seismic performance LED good.
LED chart shown below
  
LED is the core of the p-type semiconductor and n-type semiconductor chip composed of the p-type semiconductor and n-type semiconductor between a transition layer, called the pn junction. In some semiconductor materials in the PN junction, the injection of a small number of carrier-carrier and the majority of the extra time will be in the form of light energy to release, thus the power to direct conversion of solar energy. PN junction and reverse voltage, a small number of hard-carrier injection, it is not luminous. This use of injection electroluminescent diodes is produced by the principle of light-emitting diodes, commonly known as LED. When it in a positive state of the work (that is, at both ends with forward voltage), the current flows from the LED anode, cathode, semiconductor crystals on the issue from the ultraviolet to infrared light of different colors, light and the strength of the currents.


Second, LED light source features
1. Voltage: LED use of low-voltage power supply, power supply voltage between 6-24 V, vary according to product, so it is a high-voltage power than the use of more secure power supply, is particularly applicable to public places.
2.'s Performance: with the consumption of energy-efficient than incandescent reduced by 80%
3. Applicability: small, each unit LED is small pieces of 3-5 mm square, you can shape into a variety of devices and appropriate to the volatile environment
4. Stability: 100,000 hours, light failure for the initial 50%
5. Response time: the incandescent lamp of the response time of milliseconds, LED lights have a response time of Nanosecond
6. Impact on the environment: no hazardous metal mercury
7. Colors: change the current can change color, light-emitting diodes easily by chemical modification methods, adjustment of the band structure and the band gap, and red-orange multicolor Yellow-green luminescence. If small current when the red LED, with the current increase, can turn into orange, yellow, green for the final
8. Price: LED prices relatively expensive, compared to incandescent lamp, a few LED on the price of an incandescent lamp with a considerable price, and are usually required by each traffic light on 300 to 500 a diode.


3, Dan Seguang LED types and their development history
PN junction of the first semiconductor made of luminous principle of LED light source available in the early 1960s. At that time, the materials used are GaAsP, the red light (λ p = 650nm), the drive current to 20 mA, the luminous flux only a few lumens per 1,000, corresponding luminous efficiency of about 0.1 lumens / watt.
The mid-1970s, the introduction of elements In and N, so that a green LED (λ p = 555nm), yellow light (λ p = 590nm) and orange light (λ p = 610nm), optical efficiency also increased to 1 lumens / watt.
By the early 1980s, a GaAlAs the LED light source, making the red LED light efficiency of 10 lumens / watt.
In the early 1990s, red, yellow, green and the GaAlInP, the Blu-ray GaInN two of the successful development of new materials, so that the LED light effect be substantially improved. In 2000, which caused the LED in red, orange zone (λ p = 615nm) optical effect to reach 100 lumens / watt, while the latter made of green LED in the region (λ p = 530nm) optical efficiency can reach 50 lumens / Watts.


4, Dan Seguang LED Application
Instruments used for the first LED light source instructions, but all kinds of light colored LED lights in traffic and large screen has been widely applied, have a very good economic and social benefits. The 12-inch red traffic lights as an example, is used in the United States have long life, low-efficiency 140 watt incandescent lamp as a light source, it produced 2,000 lumens of white light. The red filter, the loss-90 percent, only 200 lumens of red light. In the light of the new design, Lumileds companies have 18 red LED light source, including the loss of circuit, a total power consumption of 14 watts to generate the same optical effect.
Automotive LED lights is also the source of important areas. In 1987, China began to install high in car brake lights, the LED fast response (nanosecond), can be followed as early as possible so that drivers know that traffic conditions, reducing vehicle collision accidents.
In addition, LED lights in the outdoor red, green, blue full-color displays, micro-torch-key chain, and other fields have been applied.


5, the white LED development
    For general lighting, people need more white light sources. 1998, the white LED successful development. This is the GaN LED chip and Yttrium Aluminum Garnet (YAG) package together cause. GaN chip of the Blu-ray (λ p = 465nm, Wd = 30nm), made of high-temperature sintering of the Ce3 + YAG phosphors excited by this Blu-ray after a yellow light-emitting peak 550 nm. Blue-chip installed in the LED-based Wanxing reflection in the cavity, covered with a resin mixed with YAG thin layer, about 200-500 nm. LED-based tablets issued by the Blu-ray absorption part of the phosphor, the phosphor another part of the Blu-ray and a yellow light mixed, can be a white. Now, the InGaN / YAG white LED, YAG phosphor by changing the chemical composition of the phosphor layer and adjust the thickness of the 3500-10000 K color temperature can be colored white. (Shown below)
  
  
Table 1 presents the current white LED luminescence and the type of principle. Has been the first commercialization of products for blue-chip with yellow YAG phosphor, the best luminous efficiency is about 25 lumens / watt, YAG and more on Asia for Japan's imports, prices in 2000 yuan / Kg; second is Japan's Sumitomo Electric has developed materials to ZnSe for the white LED, but less luminous efficiency.
From the table can also see that certain types of white LED light source can not be separated from the four phosphor: the three primary colors of rare earth red, green, blue and garnet powder structure of the yellow powder, was more optimistic about the future of the three-wavelength , That is inorganic UV-chip and three RGB color phosphors for white LED package is expected at the three white LED this year, the commercialization of opportunities. But here the three primary colors phosphor request relatively small size, stability requirements, specific applications are explored.

   
   Table 1 and type of white LED Principle


Chip few excited luminescence principle source of luminous materials
A blue LED InGaN / YAG InGaN blue and yellow light YAG mixed into the white
Blue LED InGaN / InGaN blue phosphor stimulate the three primary colors red, green blue, white phosphor
Blue LED ZnSe issued by the Blu-ray films of the substrate and stimulate the yellow light blending into white
UV LED InGaN / phosphors excited by ultraviolet InGaN the three primary colors red, green blue, white phosphor
2 blue LED
Aureoviride LED InGaN, GaP will have completed the two-chip package with a white LED
3 blue LED
Green LED
Red LED InGaN
AlInGaP will be the three primary colors of the three small-package together, a white LED
A number of multi-colored LED InGaN, GaP
AlInGaP will be visible across a variety of areas-chip package with a white LED

LED light source used for lighting, first of all replace the incandescent power, and then gradually enter the market to the entire lighting will save a lot of power. Recently, the white LED has reached more than one single watt of electricity, light output of 25 lumens, also increased its practicability. Table 2 and Table 3 lists the performance of white LED progress.


    Table 2 single white L ED progress in the performance


Year luminous efficacy (lumens / W) Remarks
1998 5
199 15 comparable incandescent
2001 25 similar Luwu Deng
2005 50 estimates

     Table 3 long-term development goals


Single white LED
10 watts input power
Luminous performance of 100 lumens / watt
1,000 lumens of light energy output / watt