As the light distribution and protection components of lighting products, the shell directly affects the lighting effect and life of lighting products. The engineering plastics used now are generally PC (polycarbonate), which has the best anti-aging, anti-ultraviolet and impact-resistant effects. PMMA (acrylic) is also used, its weather resistance is slightly worse, and it is more brittle and brittle. The PC material itself is colorless, and different colorants can be processed by adding different colorants according to the needs. Generally, the commonly used PCs are transparent and milky white. The transparent brightness is higher than that of milky white, but the color mixing of milky white is better than that of transparent PC.
The design of outdoor LED lighting fixtures should comply with the latest technical specifications for outdoor lighting fixtures promulgated by China, as well as rural road lighting design specifications. Due to the harsh working environment of LED outdoor lighting fixtures, it is affected by wind, rain, sun exposure, ultraviolet radiation in the sun, changes in temperature difference between day and night, sand and dust in the air, chemical gases and other conditions, and the lamps are subject to natural aging treatment year after year. , the influence of these factors should be fully considered in the design.
The LED lamp housing and the radiator are designed as a whole, which can solve the heating problem of the LED. Generally, aluminum or aluminum alloy, copper or copper alloy, and other alloys with good thermal conductivity are selected. The heat dissipation methods include air convection heat dissipation, strong wind cooling heat dissipation and heat pipe heat dissipation. The choice of heat dissipation method has a direct impact on the cost of lamps and lanterns. It should be comprehensively considered and the best solution should be selected with the design product.
The design and selection of the lampshade is also very important. Currently, transparent plexiglass, PC materials, etc. are used. The traditional lampshade is a transparent glass product. What kind of material for the lampshade is related to the product grade positioning of the design. Generally speaking, outdoor lamps and lanterns The lampshade is preferably a traditional glass product, which has a long service life and is the best choice for high-end lamps. Lampshades made of transparent plastic, plexiglass and other materials are better for indoor lamps, but have a limited lifespan for outdoor use, because outdoor sunlight, ultraviolet rays, sand and dust, chemical gases, and changes in temperature between day and night shorten the aging life of the lampshade. , and the second is that the pollution is not easy to clean, which reduces the transparency of the lampshade and affects the light output.
(1) Heat dissipation design.
Most LED lighting applications require some level of miniaturization, which often results in higher power densities, albeit not very much. Adequate thermal management measures must be provided by an improved mechanical structure. In addition, high electrical efficiency helps reduce power consumption. If further thermal resistance reduction is required, this can be done through electrical isolation as it allows for the most efficient heat transfer, these methods also allow for optimized lumen output.
Another idea to prevent the LED from overheating for a long time is to use a dimming solution. Compared with fluorescent lamps and incandescent lamps, using a dimming solution is an important way to reduce the power consumption of LEDs. This solution uses a dimming controller to achieve , especially for LED drive solutions for outdoor lighting, due to the requirements of protection level, the problem of heat dissipation is inevitable, so the choice of heat dissipation scheme is more important.
In fact, within the power range of road lighting, LED lighting fixtures will replace halogen lamps and compact fluorescent lamps (CFLs). In addition, advanced technology must remove passive components sensitive to temperature changes, such as electrolytic capacitors, in order to get rid of heat dissipation problems. . However, most current LED driver solutions are derived from and based on power topologies, so temperature range limitations should be considered, as general products are usually based on commercial standards, but lighting fixtures must ensure that they can withstand harsh environments such as The enclosure protection level of high-power LEDs used to make outdoor lamps in industrial environments is generally above IP65. If the enclosure is made of non-metallic (such as plastic) materials, although the LED is connected to an aluminum substrate (MCPCB), the heat on the aluminum substrate cannot be If it is effectively conducted to the surface of the casing, the accumulated heat will cause the temperature of the aluminum substrate to rise sharply, resulting in an excessively high temperature, increasing the possibility of LED failure, resulting in aggravated LED light decay and shortened life.
There are many difficulties in theoretically calculating the heat conduction theory of lamps. The main difficulty is that conduction and convection play a role in heat conduction at the same time, while convection is convection in a closed cavity, and the boundary conditions are very complicated; For multi-layer interfaces, the cross-sectional areas are usually not equal, resulting in the distribution of heat flow lines that are difficult to obtain by analysis before calculation.
Since the lamp gradually heats up after being turned on, and finally reaches a thermally stable state, that is to say, the temperature of each point is the highest in the thermally stable state, so the heat dissipation calculation of the lamp generally only considers the steady state, and the transient temperature distribution does not important.
Since the structure of the lamp is composed of a variety of media, in the actual calculation, it is necessary to solve each medium one by one. It is very difficult and unnecessary to calculate the temperature field distribution in the lamp. In fact, the concern is whether the temperature of certain parts is within the tolerable temperature range, as long as the temperature of these parts is calculated when they reach thermal stability.
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