LED outdoor lighting design considerations

The design of outdoor LED lighting fixtures should comply with the latest technical specifications for outdoor lighting fixtures promulgated by our country, as well as urban road lighting design standards.

1. Working Environment

LED outdoor lighting fixtures are subject to harsh working environment, wind, rain, sun, ultraviolet radiation, temperature difference between day and night, dust and chemical gases in the air, etc. The lighting fixtures are subject to natural aging year after year. The influence of these factors should be fully considered during design.

2. Selection of LED lamp materials and heat dissipation methods

The shell and the heat sink are designed as one 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 thermal conductivity are selected. There are air convection cooling, strong wind cooling and heat pipe cooling. (Jet cooling is also similar to heat pipe cooling, but the structure is more complicated.)

The choice of heat dissipation method has a direct impact on the cost of the lamp. It should be considered comprehensively and the best solution should be selected in conjunction with the designed product.

The design and material selection of lampshades are also crucial. Currently, transparent organic glass, PC materials, etc. are used. Traditional lampshades are made of transparent glass. The choice of lampshades depends on the product grade of the design. Generally speaking, the lampshades of outdoor lamps are preferably traditional glass products, which are the best choice for manufacturing long-life, high-end lamps. Lampshades made of transparent plastic, organic glass and other materials are better for indoor lampshades, but their lifespan is limited when used outdoors, because outdoor sunlight, ultraviolet rays, dust, chemical gases, day and night temperature changes and other factors shorten the lifespan of lampshades due to aging. Secondly, pollution is not easy to clean, which reduces the transparency of the lampshade and affects the light output.

3. LED chip packaging

At present, most of the LED lamps (mainly street lamps) produced in China are assembled by connecting multiple 1W LEDs in series and parallel. This method has higher thermal resistance than products with advanced packaging technology, and it is not easy to produce high-quality lamps. Or 30W, 50W or even larger modules are used for assembly to achieve the required power. The packaging materials of these LEDs are epoxy resin packaging and silicone packaging. The difference between the two is that epoxy resin packaging has poor heat resistance and is prone to aging over time. Silicone packaging has better heat resistance and should be carefully selected when used.

The author's opinion is that it is better to use multi-chip and heat sink overall packaging, or to use aluminum substrate multi-chip packaging and then connect it to the heat sink through phase change material or heat dissipation silicone grease. The thermal resistance of the product is one or two less than the thermal resistance of the product assembled with LED devices, which is more conducive to heat dissipation. For lamps using LED modules, the module substrate is generally a copper substrate. It is necessary to use good phase change material or good heat dissipation silicone grease to connect it with the external heat sink to ensure that the heat on the copper substrate can be transferred to the external heat sink in time. If it is not handled properly, it is easy to cause heat accumulation and cause the temperature of the module chip to rise too high, affecting the normal operation of the LED chip. The author believes that multi-chip packaging is suitable for manufacturing ordinary lighting fixtures, and module packaging is suitable for manufacturing compact LED lamps in limited space (such as car main lighting headlights, etc.).

4. Radiator design

The heat sink is a key component of LED lamps. Its shape, volume, and heat dissipation surface area must be designed appropriately. If the heat sink is too small, the operating temperature of the LED lamp will be too high, affecting the luminous efficiency and life. If the heat sink is too large, more materials will be consumed, increasing product costs and weight, and reducing product competitiveness. It is very important to design a suitable LED lamp heat sink. The design of the heat sink has the following parts:

1. Clarify the power that the LED lamp needs to dissipate heat.

2. Some parameters used in designing the heat sink: specific heat of metal, thermal conductivity of metal, thermal resistance of chip, thermal resistance of heat sink, thermal resistance of surrounding air, etc.

3. Determine the type of heat dissipation to be used (natural convection cooling, strong air cooling, heat pipe cooling, and other heat dissipation methods). From the cost comparison: natural convection cooling has the lowest cost, strong air cooling has medium cost, heat pipe cooling has a higher cost, and jet cooling has the highest cost.

4. Determine the maximum operating temperature allowed for the LED lamp (ambient temperature plus the allowed temperature rise of the lamp).

5. Calculate the volume and heat dissipation area of ​​the radiator and determine the shape of the radiator.

6. Combine the radiator and LED lamp into a complete lamp, and power it on for more than eight hours. Check the temperature of the lamp at room temperature of 39℃-40℃ to see if it meets the heat dissipation requirements to verify whether the calculation is correct. If it does not meet the use conditions, recalculate and adjust the parameters.

7. The seal between the radiator and the lampshade must be waterproof and dustproof. Anti-aging rubber pads or silicone rubber pads should be placed between the lampshade and the radiator, and fastened with stainless steel bolts to ensure waterproof and dustproof sealing.