Nan Kewei Haoming: Also talk about the maturity of LED street lights

LED street light is a new type of energy-saving road lighting electrical appliance. Compared with traditional street lighting, it has obvious advantages in energy saving, life, light distribution and brightness control. However, as stated in the article "The judgment of the advantages and disadvantages of LED street lamps in the development process", "In this field with high functional requirements, LEDs have encountered great resistance. Obviously, LED street lamps are exposed in the current development. Some of its shortcomings. It is not difficult to see that most of the LED road lighting projects in various places have been implemented independently, and there are many problems, such as trial and error, repeated waste.

"The Study of the Advantages and Disadvantages of LED Street Lights in the Development Process" pointed out that the main obstacles hindering the development of LED in road lighting are (should also be considered by the industry):
1. Light distribution design issues;
2, heat dissipation problems;
3. Maintenance problems;
4, cost-effective issues.

In this regard, I have the following views.

First talk about the light distribution problem. The so-called light distribution is to project the light distribution to the desired position and to maximize the uniformity of the brightness. LED as a point source, better than the columnar light source and spherical light source of high-pressure sodium lamp and electrodeless lamp, through the lens light distribution, supplemented by the secondary concave mirror light distribution, the utilization factor of LED street lamp can reach 70% or more. The uniformity is also above 40% (the company is implemented on a symmetrically arranged road with a pole spacing of 35 meters and a road width of 14 meters). There is no doubt that its luminaire utilization factor and uniformity are superior to high-pressure sodium lamp street lamps.

About the heat issue. LED is a kind of optoelectronic device, but only part of the electric energy is converted into light energy during the working process, and the rest of the electric energy is almost converted into thermal energy. Even if the luminous efficacy of the LED reaches 200 lm/W, only 29% of the electric energy is converted into light. Yes, the rest are almost always converted into heat, which raises the temperature of the LED. The LED junction temperature rise will reduce the LED light efficiency and shorten the life. When the junction temperature rises above the maximum allowable temperature, the high-power LED will be damaged due to overheating. Therefore, in the design of high-power LED lamps, heat dissipation design is the most important.

According to the experimental data of each chip manufacturer, the luminous efficiency of white LEDs decreases with the increase of junction temperature, and the luminous efficiency decreases by about 5% for every 20 °C increase in junction temperature (see Figure 1 and Figure 2). . The white LED life model of each chip manufacturer has a large difference in the relationship between the life of the white LED and the junction temperature due to the different manufacturing processes (see Figure 3 and Figure 4).

Posted on