Outdoor LED light fixture structure waterproof

Time：2021-06-10

Outdoor lighting fixtures need to withstand the test of snow and ice, wind and lightning, and the cost is high. Because it is difficult to be repaired on the outer wall, it must meet the requirements of long-term stable work. The LED is a delicate semiconductor component. If it is wet, the chip will absorb moisture and damage the LED, PcB and other components. Therefore, the LED is suitable for drying and low temperature. To ensure long-term stable operation of LEDs under harsh outdoor conditions, the waterproof structure design of lamps is extremely critical.

The so-called structural waterproofing is that after the combination of various structural components of the product, it has been waterproof.

Factors affecting the waterproof performance of lamps

1, ultraviolet light

Ultraviolet rays have a destructive effect on the wire insulation, the outer protective coating, the plastic parts, the potting glue, the sealing ring rubber strip and the adhesive exposed to the outside of the lamp.

After the wire insulation layer is aged and cracked, water vapor will penetrate into the interior of the lamp through the gap of the wire core. After the coating of the lamp housing is aged, the coating on the edge of the casing is cracked or peeled off, and a gap may occur. After the plastic case ages, it will deform and crack. The aging of the electronic potting gel causes cracking. The sealing rubber strip is aging and deformed, and a gap will occur. The adhesive between the structural members is aged, and a gap is also formed after the adhesion is lowered. These are all damage to the waterproof ability of the luminaire by ultraviolet light.

2, high and low temperature

The outdoor temperature varies greatly every day. In summer, the surface temperature of the lamps can rise to 50-60 °C, and the temperature drops to 10-20 qC in the evening. The temperature in winter and snow can drop to below zero, and the temperature difference changes more throughout the year. Outdoor lighting in the high temperature environment in summer, the material accelerates aging deformation. When the temperature drops below zero, the plastic parts become brittle, under the pressure of ice and snow or cracking.

3, thermal expansion and contraction

Thermal expansion and contraction of the lamp housing: The temperature changes cause the thermal expansion and contraction of the lamp. Different materials (such as glass and aluminum profiles) have different linear expansion coefficients, and the two materials will be displaced at the joint. The process of thermal expansion and contraction is repeated continuously, and the relative displacement is repeated continuously, which greatly damages the airtightness of the lamp.

Internal air thermal expansion and contraction: The condensation of water droplets on the buried lamp glass can often be observed on the square floor, and how does the water droplets penetrate into the lamp filled with potting glue? This is the result of respiration during thermal expansion and contraction.

For example, when the temperature is lowered from 60 ° C to 10 ° C, the internal pressure change of the lamp is about: 1 (273 + 60) K / (273 + 10) K = 0.18 atm = 1.86 m water column

When the temperature rises, under the action of huge negative pressure, the humid air penetrates into the inside of the lamp body through a small gap in the material of the lamp body, and then encounters the casing of the lamp with a lower temperature, condenses into water droplets and gathers. After the temperature is lowered, the air is discharged from the lamp body under the action of the positive pressure, but the water droplets remain attached to the lamp. The breathing process of temperature changes is repeated every day, and there is more and more water inside the lamp.

The physical changes of thermal expansion and contraction make the waterproof and airtight design of outdoor LED lamps become complex system engineering.

Luminaires based on structural waterproof design need to be tightly matched with silicone sealing ring. The outer casing structure is more precise and complicated. It is usually suitable for large-sized lamps, such as strip floodlights, square and circular floodlights, etc. Lighting.

Structural waterproof luminaires are only assembled in pure mechanical structure, using

The tool is simple, the assembly process and process are few, the final assembly cycle is short, and the repair on the production line is convenient and quick. The luminaires can be packaged and shipped through electrical performance and waterproof testing, and are suitable for engineering projects with short lead times.

However, the structure of the waterproof design of the luminaire has higher requirements for machining, and the dimensions of each component must be precisely matched. Only the right materials and constructions can guarantee the waterproof performance, the following design points.

(1) Design silicone waterproof ring, choose the material with the right hardness, design the appropriate pressure, and its cross-sectional shape is also very important. The cable entry line is a channel for water seepage. The waterproof cable should be selected. The strong cable waterproofing head (PG head) can prevent the water vapor from penetrating from the gap of the cable core, but the long-term strong extrusion of the wire insulation layer in the PG head. Press without aging and no cracking.

(2) At room temperature, the coefficient of linear expansion of glass is about 7.2×10~m/(m•K), and that of aluminum alloy is about 23.2×10 0 m/(m•K). Care must be taken when the outer dimensions of the luminaire are large. Assume that the length of the luminaire is 1 000 mm, the case temperature is 60 ° C during the day, the temperature drops to 10 ° C in the rain or night, the temperature drops by 50 ° C, the glass and aluminum profiles shrink by 0.36 mm and 1.16 mm, respectively, and the relative displacement is 0.8 mm. The sealing element is repeatedly pulled during the repeated displacement process, which affects the airtightness.

(3) Many medium and high-power outdoor LED lamps can be installed with waterproof and breathable valves (respirator). The waterproof and breathable functions of the molecular sieves in the respirator can be used to balance the internal and external air pressure of the lamps, eliminate the negative pressure, prevent the inhalation of water vapor, and ensure the internal drying of the lamps. This cost-effective waterproof device can improve the waterproof performance of the original structure design. However, the respirator is not suitable for burying lamps, underwater lights, and the like that are often in the water.

The long-term stability of the waterproof structure of the luminaire is closely related to its design, performance of the selected lamp material, processing accuracy, and assembly technology. If the weak link is deformed and seeps, it will cause irreversible damage to LEDs and electronic devices, and this situation is difficult to predict during the factory inspection process and is sudden. Therefore, to improve the reliability of structural waterproof lamps, it is necessary to continue to improve the waterproof technology.