Semiconductor lighting concept briefly described and development
Semiconductor lighting, also known as LED lighting, LED (LightingEmittingDiode) that is, light-emitting diode, is a semiconductor solid light-emitting device.
It is the use of solid semiconductor chips as light-emitting materials, in the semiconductor through the carrier composite compound to release excess energy and cause photon emission, directly emit red, yellow, blue, green, cyan, orange, purple, white light.LED lighting products is the use of LED as a light source manufactured by the lighting apparatus.
First, the principle of LED lighting
LED is made of Ⅲ-IV compounds, such as GaAs (gallium arsenide), GaP (gallium phosphide), GaAsP (gallium arsenide phosphorus) and other semiconductors, the core of which is the PN junction. Therefore, it has a general P-N junction of I-Mitsufuji photoelectric N characteristics, that is, forward conduction, reverse cutoff, breakdown characteristics. In addition, under certain conditions, it also has light-emitting properties. Under forward voltage, electrons are injected into the P region from the N region, and holes are injected into the N region from the P region. Into each other region of the minority carriers (oligon) part of the majority of carriers (polyon) and the complex and luminescence.
Assuming that the luminescence occurs in the P region, then the injected electrons and valence band holes are directly compounded and luminescence, or first by the luminescence of the center of capture, and then compounded with the hole luminescence. In addition to this luminescence composite, there are also some electrons are non-luminescent center (the center of the conduction band, the middle of the band near) capture, and then with the hole composite, each time the release of energy is not large, can not form visible light. Luminescent composite amount relative to the non-luminescent composite amount of the larger the ratio, the higher the light quantum efficiency. As the composite is in the oligon diffusion region of the light-emitting, so the light is only generated within a few μm near the PN junction surface.
Theory and practice have proved that the peak wavelength of light λ is related to the forbidden bandwidth Eg of the semiconductor material in the luminescence region, i.e.
λ≈1240/Eg (mm)
Where the unit of Eg is electron volt (eV). If visible light (wavelength in 380nm violet ~ 780nm red light) can be produced, the semiconductor material Eg should be between 3.26 ~ 1.63eV. Light longer than the wavelength of red light is infrared light. Now there are infrared, red, yellow, green and blue light-emitting diodes, but the cost of blue light diodes, the price is very high, the use is not universal.
Second, the significance of the limit parameters
(1) allow power consumption Pm: allowed to be added to both ends of the LED forward DC voltage and the current flowing through it the maximum value of the product. More than this value, LED heat, damage.
(2) Maximum forward DC current IFm: the maximum allowable forward DC current. Exceeding this value can damage the diode.
(3) Maximum reverse voltage VRm: the maximum allowable reverse voltage. Exceeding this value, the light-emitting diode may be damaged by breakdown.
(4) Operating environment topm: light-emitting diode can work normally in the ambient temperature range. Below or above this temperature range, light-emitting diodes will not work properly, the efficiency is greatly reduced.
Third, LED lighting development status
The current global energy shortage concerns are rising again in the context of energy conservation is an important issue facing us in the future, in the field of lighting, LED light-emitting products are attracting the world's attention, LED as a new type of green light source products, is bound to be the trend of the future development of the twenty-first century will be entering the era of new lighting light source represented by LED.
China's LED industry started in the 1970s. After more than 30 years of development, China's LED industry has initially formed a more complete industrial chain, including the production of LED epitaxial wafer, LED chip preparation, LED chip packaging and LED product applications. In the "National Semiconductor Lighting Project" to promote the formation of Shanghai, Dalian, Nanchang, Xiamen, Shenzhen, Yangzhou and Shijiazhuang seven national semiconductor lighting project industrialization base. Yangtze River Delta, Pearl River Delta, Fujian Delta and the northern region has become China's LED industry development gathering place.
At present, China's semiconductor lighting industry development is good, epitaxial chip enterprise development is especially rapid, encapsulation enterprise scale continues to maintain rapid growth, lighting applications have made greater progress. 2007 China LED application product output value has exceeded 30 billion yuan, has become the LED full-color display, solar energy LED, landscape lighting and other applications of the world's largest producer and exporter of products, the new semiconductor lighting The emerging semiconductor lighting industry is taking shape. Domestic lighting in the field has formed certain characteristics, including outdoor lighting is the fastest growing, there have been hundreds of LED street lamp enterprises and the construction of dozens of demonstration roads, but in the indoor general lighting market is still lagging behind.
Fourth, LED lighting development trend
LED is known as the fourth generation of lighting light source or green light source, with energy saving, environmental protection, long life, small size and other characteristics, can be widely used in a variety of instructions, display, decoration, backlighting, general lighting and urban night scenery and other fields. In recent years, some economically developed countries in the world around the development of LED launched a fierce technological competition. The United States from 2000 to invest 500 million U.S. dollars in the implementation of the "National Semiconductor Lighting Program", the European Union also announced in July 2000 to start a similar "Rainbow Program". China's Ministry of Science and Technology in the "863" program under the auspices of the June 2003 first proposed the development of semiconductor lighting program. Over the years, LED lighting with its energy-saving, environmentally friendly advantages, has been the attention of the state and all levels of government, around the introduction of relevant policies and initiatives to accelerate the development of LED lamps and lanterns; the mass of consumers are also on this environmentally friendly new type of lighting products for a long time. However, due to the high cost of investment in technology and promotion, so that thousands of consumers are waiting for the LED lighting products have been unattainable, the delay has not been able to unveil its mysterious aristocratic veil!
With the domestic part of the manufacturers of technology and production cost reduction, LED lighting good and not the situation will change. Inexpensive and beautiful LED lighting products, will bring a revolutionary impact on China's lighting industry, for the majority of consumers to bring the gospel of light!
Advantages:
High energy-saving: energy-saving energy without pollution that is environmentally friendly. DC drive, ultra-low power consumption (single tube 0.03-0.06 watts) electro-optical power conversion close to 100%, the same lighting effect than the traditional light source energy saving more than 80%.
Long life: LED light source some people call it a long-life lamp, meaning never go out of the lamp. Solid cold light source, epoxy resin encapsulation, there is no loose part of the lamp body, there is no filament light burning, heat deposition, light decay and other shortcomings, the service life of up to 60,000 to 100,000 hours, more than 10 times longer than the life of traditional light sources.
Multi-variable: LED light source can use red, green, basket three-color principle, under the control of computer technology so that the three colors have 256 levels of gray scale and arbitrary mixing, you can produce 256 × 256 × 256 = 16777216 kinds of colors, the formation of different combinations of light color changeable, to achieve colorful and dynamic changes in the effect of a variety of images.
Lee environmental protection: better environmental benefits, no ultraviolet and infrared in the spectrum, neither heat, nor radiation, glare, and waste can be recycled, no pollution does not contain the element of mercury, cold light source, can be safe to touch, belongs to the typical green lighting light source.
High-tech: compared with the monotonous luminous effect of the traditional light source, LED light source is a low-voltage microelectronic products, the successful integration of computer technology, network communication technology, image processing technology, embedded control technology, etc., so it is also a digital information technology products, semiconductor optoelectronic devices, "high and new" technology, with online programming, unlimited upgrades, flexible and versatile features. It has the characteristics of online programming, unlimited upgrading, flexibility and versatility.
Fifth, the scope of application of LED lighting
LED lighting fixtures, bottom lights, chandeliers, projector lamps and other decorative, reflective use of LED lighting fixtures can be fully capable of any occasion, including art galleries, museums and other places with high color requirements. However, for large-scale facilities such as shopping malls and office buildings, although LED lamps have been created as a wide range of lighting, their directionality (the light emitted by the LED chip is straight, and the dispersion is not good) is too high, which makes it difficult to design an average illuminance over a large area. Tube-type LED lighting fixtures are arranged too closely, the design cost is too high, losing energy-saving effect. Therefore, at this stage of decorative use occasions, LED lighting fixtures are fully available, large-area indoor lighting is still immature.
Six, LED lighting advantages and disadvantages
Compared with other light sources, LED semiconductor light source is called "green light source" deservedly. In the lighting industry, its comparative analysis with the traditional light source, some aspects of the performance of the advantages of irreplaceable:
(1) high luminous efficiency. Incandescent lamps, tungsten halogen lamp efficiency of 12 ~ 24 lm / W, fluorescent lamps 50 ~ 70 lm / W, sodium lamps 90 ~ 140 lm / W. LED light efficiency will be improved to reach up to 50 ~ 200 lm / W, and its light monochromatic, spectral narrowing, no need for filtering can be directly issued by the colored visible light.
(2) less power consumption, LED single tube power 0.03 ~ 0.06 W, using DC drive, single tube drive voltage 1.5 ~ 3.5 V, current 15 ~ 18 mA, fast response time, can be operated at high frequencies. The same lighting effect, power consumption is one-eighth of the incandescent bulb, one-half of the fluorescent tube.
(3) Long service life. The use of LED lights are small, lightweight, epoxy resin encapsulation, can withstand high-intensity mechanical shock and vibration, not easy to break. The average life expectancy of 100,000 hours.
(4) Brightness and color of the dynamic control is easy. Available red, green and blue elements into a variety of different colors, can achieve continuously adjustable brightness, high color purity, color dynamic transformation and digital control; can accurately control the light pattern and light-emitting angle, the light color is soft, no glare.
(5) Flexible size. Small size, can be combined at will, easy to develop into a lightweight thin and short small lighting products, but also easy to install and maintain.
(6) environmentally friendly. LED for the whole solid emitter, shock resistance, impact resistance is not easy to break, the waste can be recycled, no pollution. Does not contain mercury, sodium and other substances that may be harmful to health.
But LED and other light sources also have insufficient aspects, such as low color rendering in white lighting. Currently with yellow phosphor and blue light produced by the white LED, as general lighting can be, but for some of the high color resolution requirements of the place is inadequate. Through the incandescent lamp, fluorescent lamp, ordinary LED and high-power LED life comparison, can see that the high-power LED in the life of a great advantage, incandescent and fluorescent lamps in many technical aspects of the promotion of space has been very small.