Semiconductor light-emitting diodes (LEDs) have a history of more than forty years. After the emergence of blue-light LEDs in the first half of the 1990s, white LEDs were quickly solved. The advent of white LED and its rapid development have attracted the attention of the world's lighting companies. They have invested a lot of money and conducted fruitful research. In the past ten years, the light efficiency of white LED has been improved by nearly ten times. A new type of solid-state light source (SSL) enters the field of illumination and becomes the third generation of new light sources after the second generation (gas discharge lamp).

1 Advantages of white LED

White LED has appeared for nearly 15 years, and its development speed is faster than people's expectations. It seems to be a super-developed juvenile "child prodigy", which has received special attention and cultivation from the family and society. Its main advantages and features are:

(1) Rapid improvement of light efficiency: Up to now, the practical light efficiency of the product can reach 70-90lm/W. According to reports, the US laboratory data reaches 160lm/W, and there is an increasing trend, which is expected to be 3~5 in the future. In the year, it is possible to achieve a practical light effect of 150 to 200 lm/W, and by then it is possible to become the most efficient light source.

(2) The starting performance is good, fast and reliable, and only the response time of milliseconds can reach the all-optical output.

(3) Convenient dimming and strong controllability.

(4) It is resistant to vibration, weather resistance and long life.

(5) Contains no mercury and has excellent environmental performance.

(6) LEDs are directed to radiate within a certain beam angle, and are used for spotlights, downlights, etc., to improve the downlight ratio.

(7) For landscape, decoration, advertising, signal and other occasions, there are a variety of colored light LEDs, plus good start-up and dimming performance, easy to achieve digital control, to achieve colorful, dynamic changes, in commercial, entertainment The venue is highly rendered.

2 white LEDs for indoor lighting to be solved

White LEDs are advancing in the field of lighting, and have been continuously improved in practical applications. Many achievements have been made and the development of LED lighting has been promoted. LED has been used in night lighting, which has shown great advantages. However, as a functional lighting, it is far from mature in terms of product or technology. There are still many problems to be solved. Of course, this is also true. The main problems in the development of law are:

(1) LED chips mainly rely on imports, there are few domestic chips, high-power (1W and above) chips are not available, chips lack their own technology and intellectual property; China has a large-scale LED packaging industry, with better Equipment, but packaging technology, materials and processes, there is still a gap.

(2) Lack of uniform standards, including LED lighting systems, drive circuits, etc. Some enterprises have developed their own advantages, researched and developed their own products, and some have borrowed or copied them. The level of products varies, and the scale of each product varies. Poor sex and difficult maintenance.

(3) There is no uniform test method for LED lighting. Some parameters are still to be tested. For example, color measurement and gas discharge lamps are not necessarily the same.

(4) LED lighting products are still in the initial stage, technically immature, and there are still many problems, such as:

1) Heat dissipation problem: How to effectively reduce the junction temperature to the allowable level, still in the exploration and practice, the temperature control is not good, it will affect the light effect, the attenuation of the light pass, and even the color temperature and color rendering stability.

2) At present, most LEDs have high color temperature and excessive blue spectrum. For most indoor places, people will feel uncomfortable, produce a sense of excitement, and are not coordinated with the environment. The light is not soft enough, which is not conducive to eye protection.

3) LED is used as indoor functional lighting. How to design the light distribution and light control system of the luminaire is also a new subject. The directional LED is different from the existing light source. The reflection, diffusion and light distribution of the luminaire have their own Features.

4) LED lighting drive circuit: It also needs further optimization and standardization. It takes time, its performance including life, power consumption, harmonics, power factor, etc., need to be explored.

(5) The price is too high, which is another obstacle to the promotion and application. Government subsidies alone are not a good strategy for development. LEDs are used to replace inefficient light sources such as incandescent lamps, which have significant energy-saving effects and can enjoy subsidies. More efficient light sources such as fluorescent lamps do not have energy-saving effects (at least today), and the high initial cost is not economically justified.

(6) Another problem with LED lighting is the lack of a smooth and orderly development. In just a few years, thousands of companies have squeezed into LED lighting, and there is a rising posture that reminds people of the "Great Leap Forward" era. Some companies have made imitations, low-level repetitions, exaggerated market entry, some companies and some media integration, excessive hype, exaggerated energy-saving effects, and even individual government officials have also taken the role of fuel, misleading the use of units. It is necessary to establish a complete set of technical standards and objective evaluation mechanisms, and seek truth-seeking public opinion to guide its healthy development.

3 LED role in indoor lighting

3.1 Principles and directions of application

Indoor lighting is different from night lighting, and emphasizes the function of lighting. Compared with road lighting, it is a wider space. Different places of use, different functions, different sizes, different decorative aesthetic requirements, determine indoor There are many kinds of lighting fixtures, and the types of light distribution are different. At present, hundreds of enterprises are rushing to the streetlights. They should broaden their horizons, change their minds, and enter the wider world.