The LED as the latest occurrence of lighting technology, since 1960s, LED has been long-term development and application. To compare with incandescent, fluorescent and other older light-emitting devices, LED’s features are mainly reflected as the follows:
1.Voltage: The LED is a low-voltage devices, a single LED driver is only 2.5-3V, which is safe will not cause electric accident ,also be suitable for many low-voltage and low power supply places.
2.Energy-consuming: energy consumption is reduced 80% compare with same light efficiency incandescent.
3.Applicability: due to its characteristic of small volume, light weight and thickness, it can extend various shapes devices with various shapes devices, and be fit for the changeable environment.
4.Stability: After 100000 hours, the light failure still have half of the initially.
5.Response time: the incandescent response time is the millisecond, the LED response time for the nanosecond.
6.Environment protection: There is no harmful metallic mercury in LED.
7.Color: different chip materials can obtain different monochrome LED, but the same chip materials using different epitaxial wafer , LED light color is also different. LED conveniently through chemical modification methods to adjust the band structure and forbidden band width of material, which can realize such as red,yellow,green,blue,orange and other multi-color light.
8.Price: The LED’s price is more and more common, due to its electric-saving, we can predict that people replace incandescent with the LED light in the near future. Atpresent, some cities in China’s road,schools,factories and other places have change the LED street light, garden light etc.
9.Good seismic performance:.LED is a kind of electroluminescent light source, its structural characteristics determine the smaller the influence of vibration.
Monochromatic light LED features and history
The LED was born in 1960s, which was made of GaAsP at that time and show up the red light. When the driver current is 20mA, then luminous flux is lower than 10‰.
In the middle of 1970s,having green(wavelength is 555nm) light,yellow(wavelength is 590nm) and orange(wavelength is 610nm) light with steel elements and nitrogen element.
In the early 1980s, the GaAlAs LED light source is occurred, which make the red LED light efficiency reach 10lm/w.
In the early 1990s, the InGaAlP show the red light,yellow light ,and blue light (InGaN) is occ
rred successfully, so that the LED light efficiency has been greatly improved.
In 2000, GaAlP LED wavelength is 615nm at the red&orange area,it efficiency reach 100lm/w, InGaN LED wavelength is 530nm at the green area,it efficiency reach 50lm/w latter in the green(wavelength is 530nm) area of the light efficiency reach 50lm/w. In 2011, the LED can show up red, yellow, blue, green, orange, fine color, blue green double color, red, green, double color, yellow green color, pure green, green, white and other lights.
Now led light efficiency can reach 150 lm/w,even higher.
As for general lighting, people need the white light source more.
In 1998, the white light LED had successfully researched and developed, which is made of GaN chip and YAG packaging together. GaN chip shows up the blue light(wavelength is 465nm) , high-temperature sintered YAG phosphor containing Ce3+ was met by blue light and shows up the yellow light, its peak measure is 550nm. The blue LED substrate is installed in the bowl reflection cavity, covered with mixed with resin layer of YAG, which thickness is about 200-500nm.
The blue light showed up by LED substrate is partially absorbed by the phosphor, the other will mix the yellow light showed up by the phosphor, thus it obtains the white light. As for InGaN/YAG white LED, it can obtain color temperature is 3500-10000k various white colors by changing the chemical composition of YAG phosphor and adjust the powder layer’s thickness.
The light-emitting mechanism of Semiconductor material determined the single LED cannot launch a continuous spectrum of white light, must synthesize light in other ways.
Now there are two ways to produce white light :one is the monochromatic light can stimulate phosphors show up other color light, then the white light is produced, this is called single-chip types; the other is to mix several color light package together, so that the white LED light is also produced, which called more-chip types.
Single-chip structure can be classify three types:
- Combine the blue LEDGalnN chip with yttrium aluminum garnet (YAG) phosphor, so that it produces two basic color white LED, or the InGaNcombine with red, green phosphor powder to form three basic color white LED.
- The blue ZnSe can be made a chip as the substrate, which recombine with its yellow light to form the white light.
- The ultraviolet light showed by InGaN LED can stimulate the three-basic-color phosphor powder to show up white light.
Monochromatic light LED application
Originally, LED was used as the indicating light source for instrumentation, and then all kinds of colored LEDs were widely used in traffic lights and large displays, which had very good economic and social benefits. Such as the 12in red traffic light,before it is 140W incandescent light as a light source in the United States ,which was a long lifespan, low light efficiency , it produces 2000lm white light. After the red filter, the light loss 90% .then red light left is 200lm.
However, in new LED design, the Lumileds corporation adopts 18 red LED light source, include the light circuit losses, a total of 14W power consumption. So 14W Led source is equal to 140W incandescent light.
The car light is also an important field of LED light source application. In 1987, China began to install high-speed brake lights in the car, due to its fast response time, you can let the following drivers know the driving conditions as soon as possible, it reduces the traffic accident in a certain percent.
In addition, the LED light has been applied in the outdoor red, green,and blue full-color display screen, key chain micro-torch and more other fields.
The appearance of white LED light is to take a substantive step from the marking function to the lighting function. The white light closest the sunlight, which can better reflect the true color of the illuminated object, therefore, from a technical point of view, the white light is undoubtedly the most cutting-edge LED technology.
The white LED light is widely used in many fields, and also “kill” or replace the incandescent-tungsten- filament lamp and fluorescent lamp . At present, the white LED light has already entered many application field, such as emergency-light, flashlight ,floodlight,high bay light,wall light and others . Depends on technological progress,there is no doubt the white LED light popularity is coming, the LED white light have forms a certain market size. Now the white LED light forming a certain market size, so it can be seen everywhere.