LED street lights need to crack the technical difficulties
LED street lights in order to scale the application to become a mainstream source of road lighting, are still facing some difficult points that need to be addressed. To sum up, the main difficulties in three, optical design, thermal issues and drive power supply design.

1. optical design

Easy optical design was a big advantage of the LED street lights, but at the same time is a major difficulty.

From the point of view of LED street lights with light, its light output characteristics only meet as shown in Table 2 CJJ45-2006 road lighting standards requirements have practical value.

LED street lights with light including a light distribution (encapsulated lens), the second with the light and three light distribution. When the secondary light distribution to meet the the pavement brightness, illumination uniformity requirements, you no longer need three times optical design. To meet the requirements of the road lighting, LED lights with light must undergo repeated design can be achieved.

Three light distribution reflector LED street light distribution program been developed, such as LED light distribution (ie lens package) plus lamps secondary light distribution and LED secondary light distribution (using secondary lens) plus lamps light distribution, etc., but no matter what kind of light distribution program, can not be a scientific and reasonable, to varying degrees, the overall optical efficiency is low, there is a larger glare and surface brightness, illumination uniformity and poor. How to choose the light distribution, how to choose lenses, how to improve the structure of the street lamps to achieve with light and heat requirements are solutions also need to be more mature.

2. heat problem

The cooling capacity of the LED street light directly affect the the actual LED luminous efficiency of its life.

The LED is electrically electroluminescent device, only 15% to 25% of the energy is converted into light in the course of their work, and the rest of the energy is almost converted into heat, so that the elevated temperature of the LED, resulting in the sharp decline of the luminous efficiency. If the LED junction temperature exceeds the maximum allowable temperature (125 ° C), the LED will be damaged by overheating. LED lighting design, the most important of a work is the thermal design.

The LED lights cooling system including cooling and lighting LED module structure (such as housing) on ​​the heat sink cooling, the latter of which is a common cooling mode, the LED street lights work environment was quite poor, easy to accumulate dust or sand and flies radiator surface is susceptible to corrosion and oxidation, which will affect the heat dissipation of the LED lights, and electrical LED light life shortening.

In order to solve the heat problem LED street lights can configure the miniature fan active mandatory cooling but it is difficult to meet the requirements of the cooling fan service life in harsh outdoor environments.

LED street light weight is mainly determined by the weight of the heat sink. With the increasing power of LED street lights, radiator size and weight also need to be increased accordingly. To lighten the weight of high-power LED street light heat sink, you need to optimize the design of the cooling mode, the heat dissipation structure and materials aspects.

LED street lights require good dustproof and waterproof (IP) IP45 protection class (such as above), but a good IP protection tend to impede the LED heat. How to resolve this contradiction is an important direction of LED street light design can not be ignored.

3. drive power supply design

LED lights currently almost all mains frequency power supply. LED street light drive circuit topology generally are off-line switching power supply (SMPS). From recent years, LED street light demonstration applications, failure is almost all concentrated in the drive power.

LED street light working environment is very harsh on the drive power design, the choice of circuit topology, the selection of electronic components and circuit protection, thermal and waterproof, are very demanding.

Based on existing technical level, the average life expectancy of a conventional off-line switching power supply is usually less than 30,000 hours, LED the life of the drive circuit to determine the life of the LED street lights. LED drive power life electrolytic capacitor has a decisive influence, followed by the power semiconductor devices. Therefore, the selection of the electrolytic capacitor is extremely important.

LED SMPS design, not only to pay special attention to its reliability, must also meet the input AC current harmonic content line power factor, electromagnetic interference (EMI), anti-lightning and waterproof and energy efficiency performance requirements safety requirements. Explore low-cost, high-reliability and high-performance solutions, LED SMPS design a difficulty.
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