Due to the complicated working environment, LED outdoor lighting fixtures are affected by natural conditions such as temperature, ultraviolet light, humidity, rain, rain, sand, chemical gas, etc. Over time, the problem of LED light decay is serious. Therefore, outdoor lighting designers should consider the impact of these external environmental factors on LED outdoor lighting when designing.
The outer casing and the heat sink are designed to be integrated to solve the heat generation problem of the LED. This method is preferable, and aluminum or aluminum alloy, copper or copper alloy, and other alloys with good heat conductivity are generally used. The heat dissipation has air convection heat dissipation, strong wind cooling heat dissipation and heat pipe heat dissipation. (Jet cooling heat dissipation 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.
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 it 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.
It is better to use a multi-chip and a heat sink as a whole package, or to use an aluminum substrate multi-chip package and then connect the phase change material or the heat-dissipating grease to the heat sink, and the thermal resistance of the product is higher than that of the product assembled with the LED device. Less one to 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 is to 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 will easily cause the heat accumulation to cause the module chip temperature to rise too high, which will affect 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.).
Defining the power that LED lights need to dissipate heat.
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.
Determine the type of dispersion, (natural convection cooling, strong wind cooling, heat pipe cooling, and other heat dissipation methods.) From the cost comparison: natural convection cooling lowest cost, strong wind cooling medium, heat pipe cooling cost is higher, jet cooling cost is the highest .
Determine the maximum operating temperature allowed for LED luminaires (ambient temperature plus luminaire approval temperature rise)
Calculate the volume and heat dissipation area of the heat sink. And determine the shape of the heat sink.
Combine the radiator and the LED lamp into a complete luminaire, and work on it for more than eight hours. Check the temperature of the luminaire at room temperature of 39 °C - 40 °C to see if the heat dissipation requirements are met to verify whether the calculation is correct. Conditions, then recalculate and adjust the parameters.
The seal of the radiator and the lampshade should be waterproof and dustproof. The anti-aging rubber pad or silicone rubber pad should be padded between the lamp cover and the heat sink. It should be fastened with stainless steel bolts to ensure waterproof and dustproof. Matters, with reference to the latest outdoor lighting technical specifications promulgated by China, as well as urban road lighting design standards, this is the essential knowledge of outdoor lighting designers.