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Research and development progress of Led street lights

Research and development progress of Led street lights

2021-04-02

Nowadays, LED street lights can be seen everywhere. They not only embellish the night sky, but also make a great contribution to energy conservation. However, the use of Led street lights has certain limitations, so that it has not been fully used. In order to enable LED street lights to play more roles in our lives, in the future R&D, production and promotion applications, we should solve them from the following aspects:


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1. The improvement of luminous flux also needs to be further improved from the basic level of high-power LED epitaxial technology and chip technology. The method of making white LEDs at home and abroad is to first place the LED chip on the packaged substrate, bond it with gold wire, and then coat the YAG phosphor around the chip, and then encapsulate it with epoxy resin. The resin not only protects the chip but also functions as a condenser. The blue light emitted from the LED chip hits the surrounding phosphor layer and is scattered and reflected and absorbed many times, and finally emitted to the outside. The peak of the spectral line of the LED (blue) is at 465 nm, and the half-value width is 30 nm. Part of the blue light emitted by the LED excites the yellow YAG phosphor layer, causing it to emit yellow light (peak value is 555nm), part of the blue light is emitted directly or after reflection, and the light that reaches the outside is blue and yellow light, that is, white light. FlipChip technology (FlipChip) can get more effective light emission than traditional LED chip packaging technology. However, if a reflective layer is not added under the electrode of the light-emitting layer of the chip to reflect the wasted light energy, it will cause about 8% of light loss. Therefore, a reflective layer must be added to the bottom plate material. The light on the side of the chip must also be reflected by the mirror surface of the heat sink to increase the light output rate of the device. In addition, a layer of silicone material should be added between the sapphire substrate (Sapphire) of the flip chip and the bonding surface of the epoxy resin light guide to improve the refractive index of the light emitted by the chip. Through the improvement of optical packaging technology, the light extraction rate (luminous flux) of high-power LED devices can be greatly improved.


2. Optimized design of LED lighting equipment to improve the quality of LED use. Therefore, it is particularly urgent to study the secondary optical light distribution design of high-power LED light sources to meet the light distribution needs of large-area projection and flood lighting. Through the secondary optical design technology, the design of additional reflecting cups, multiple optical lenses and aspheric light-emitting surface can improve the light extraction efficiency of the device. The illumination direction of the traditional light source is 360°. The lamp relies on the reflector to reflect most of the light to a specific direction. Only about 40% of the light reaches the road directly through the glass cover, and the other light is projected out of the lamp through the reflector of the lamp. , The efficiency of the reflector of the lamp is generally only 50%~60%, so about 60% of the light output in the lamp is projected on the road after a loss of 30%~40%. A large part of the light output of the light source is limited to the internal heating and consumption of the lamp. Most of the light of LED lights is front light, which can achieve >95% luminous efficiency. This is one of the important characteristics of LEDs that distinguish them from other light sources. If this characteristic is not used well, the advantages of LEDs will be great. discount. Since most high-power LED lights are assembled with multiple LED chips, we need to illuminate so many light sources in different directions. We give full play to the characteristics of the integrated chip package and use lenses to solve the problem. Through optical design, different convex curves are equipped according to different needs. , Relying on the lens to distribute the light to different directions, to ensure that the large light angle can reach 120°~160°, and the small one can concentrate the light within 30°. Once the lens is finalized, the same kind of lamps can be guaranteed under the premise of the production process. The light distribution characteristics of the two have reached the same level. It is completely possible to make LED street lights meet the batwing light type required by road lighting standards through repeated trials and continuous summing up of experience. Tunnel lights, street lights and general lighting have reached the lighting requirements of their respective application places.


3. Heat dissipation is a key problem that LED street lights need to solve. As we all know, LED is an optoelectronic device. During its working process, only 15% to 25% of the electrical energy is converted into light energy, and the rest of the electrical energy is almost converted into heat energy, which increases the temperature of the LED. In high-power LEDs, heat dissipation is a big problem. For example, if a 10W white light LED has a photoelectric conversion efficiency of 20%, 8W of electrical energy is converted into heat. If no heat dissipation measures are taken, the core temperature of the high-power LED will rise rapidly, when its junction temperature (TJ) When the temperature rises above the maximum allowable temperature (usually 150°C), the high-power LED will be damaged due to overheating. Therefore, in the design of high-power LED lamps, the most important design work is heat dissipation design. Due to the high brightness requirements of LED street lights, the use environment is relatively harsh, if the heat dissipation is not solved well, it will quickly cause LED aging and reduce stability. A street lamp using 250W high pressure sodium lamp, due to mature technology and good heat dissipation control, even if it works for 5000 hours, the light decay is still very small. High-power LED street lights under the same conditions, if the heat dissipation is not solved well, the light decay will be great. The heat dissipation methods of LED street lights mainly include: natural convection heat dissipation, additional fan forced heat dissipation, heat pipe, loop heat pipe heat dissipation, and uniform temperature plate heat dissipation. The forced heat dissipation method of installing a fan has a complicated system and low reliability, and the heat dissipation method of heat pipe and uniform temperature plate is costly.


4. LED street lights will eventually choose modular installation and maintenance. The most high-pressure sodium lamps used on the road, the internal ballasts and other components are not easy to damage, most of the reason for not lighting is the damage of the light source, the maintenance method only needs to replace the light source. A skilled operator can perform high-level operations personally. However, LED street lights have many internal components. Except for the light source (chip), damage to other parts will cause the chip to not light up. Therefore, at the scene, it is impossible to immediately determine the cause of the damage to the LED street light. If the LED street light does not light up, the LED street light needs to be taken off and shipped back to the factory for various tests. This way of replacing LED street lights is very cumbersome. The final version of the development of LED street lighting is to develop into modularity. The light source, electricity, etc. are all replaced in accordance with the plug-in connection, so that a skilled worker can fully independently judge the cause of the damage and perform on-site maintenance.


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