With the wide application of LED lighting equipment, LED lighting fixture design should comply with the latest outdoor lighting fixture technical specifications promulgated by China, as well as urban road lighting design standards. The following points should be noted for the design of LED lighting fixtures.
First, the working environment
LED outdoor lighting fixtures are subject to harsh working conditions, exposed to wind and rain, sun exposure, ultraviolet radiation in the sun, temperature difference between day and night, dust in the air, chemical gases and other conditions. The lamps are subject to natural ageing treatment year after year. . The impact of these factors should be fully considered in the design.
Second, LED lighting materials and cooling options
The outer casing and the heat sink are designed to be integrated to solve the heating problem of the LED. This method is better, generally aluminum or aluminum alloy, copper or copper alloy, and other alloys with good heat conductivity. The heat dissipation has air convection heat dissipation, strong wind cooling heat dissipation and heat pipe heat dissipation. (Jet cooling is also a kind of heat pipe cooling, but the structure is more complicated.)
The choice of what kind of heat dissipation method has a direct impact on the cost of the luminaire should be considered comprehensively, and the best solution should be selected in conjunction with the design product.
The design of the lampshade is also very important. Currently, there are transparent plexiglass, PC materials, etc. The traditional lampshade is a transparent glass product. What kind of material is selected is related to the design of the product grade. Generally speaking, the outdoor lamp The lampshade is preferably a traditional glass product, which is the best choice for long-life, high-end lamps. The lampshade made of transparent plastic, plexiglass, etc. is better for the indoor lamp, and the outdoor life is limited. Because of the outdoor sunlight, ultraviolet light, sand dust, chemical gas, temperature difference between day and night, etc., the aging life of the lampshade is shortened. Secondly, the pollution is not easy to clean and clean, so that the transparency of the lampshade reduces the light output.
Third, the LED chip package
At present, LED lamps (mainly street lamps) produced in China are mostly assembled by using 1W LEDs in multiple strings and parallels. This method has higher thermal resistance than advanced packaging technology and is not easy to produce high-quality lamps. Or it can be assembled with 30W, 50W or even larger modules to achieve the required power. The packaging materials of these LEDs are encapsulated in epoxy resin and encapsulated in silicone. The difference between the two is that the epoxy resin package has poor temperature resistance and is prone to aging over time. The silicone package is better in temperature resistance and should be selected when using.
The general view is: the multi-chip and the heat sink are better packaged, or the aluminum substrate multi-chip package is connected with the heat sink through the phase change material or the heat-dissipating grease, and the product thermal resistance is assembled compared with the LED device. The thermal resistance of the product is less than one or two thermal resistance, which is more conducive to heat dissipation. For the LED module, the module substrate is generally a copper substrate, and the connection with the external heat sink should use a good phase change material, or a good heat dissipation grease to ensure that the heat on the copper substrate can be transmitted to the external heat sink in time. Going up, if the processing is not good, it is easy to cause the heat to accumulate and the temperature of the module chip rises too high, which affects the normal operation of the LED chip. The author believes that: multi-chip package is suitable for the manufacture of general lighting fixtures, module packaging is suitable for space-limited occasions to manufacture compact led lamps (such as headlights for automotive main lighting, etc.).
Fourth, the design of the radiator
The radiator is a key component of the LED luminaire. Its shape, volume and heat dissipation surface area must be designed to be beneficial. The radiator is too small, the working temperature of the LED lamp is too high, affecting the luminous efficiency and life, and the radiator is too large. Then, the consumption of materials increases the cost and weight of the product, and the competitiveness of the product decreases. It is important to design a suitable LED light radiator. The design of the heat sink has the following parts:
1. Identify the power that the LED lights need to dissipate heat.
2. Design some parameters for the heat sink: the specific heat of the metal, the thermal conductivity of the metal, the thermal resistance of the chip, the thermal resistance of the heat sink, and the thermal resistance of the surrounding air.
3. Determine the type of heat dissipation (natural convection heat dissipation, strong wind cooling, heat pipe heat dissipation, and other heat dissipation methods.) From the cost comparison: natural convection heat dissipation is the lowest, strong wind cooling is medium, heat pipe cooling cost is high, jet cooling The highest cost.
4. Determine the maximum operating temperature allowed for the LED luminaire (ambient temperature plus luminaire approval temperature rise),
5. Calculate the volume and heat dissipation area of ​​the heat sink. And determine the shape of the heat sink.
6. Combine the radiator and LED lamp into a complete luminaire, and work on it for more than eight hours. Check the temperature of the luminaire under the environment of room temperature 39 °C - 40 °C to see if the heat dissipation requirements are met to verify whether the calculation is correct, if not If the conditions of use are met, the parameters are recalculated and adjusted.
7. The seal of the radiator and the lampshade should be waterproof and dustproof. The rubber pad or silicone rubber pad should be padded against the aging between the lamp cover and the heat sink. It should be fastened with stainless steel bolts to make it waterproof and dustproof.
(Edit: Technology)
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