Outdoor lighting needs to withstand the test of ice, snow, scorching sun, wind, rain and thunder for a long time, and the cost is high. Because it is difficult to dismantle and repair on the outer wall, it must meet the requirements of long-term stable work. The LED is a delicate semiconductor component. If it gets wet, the chip will absorb moisture and damage the LED, PcB and other components. Therefore, the LED is suitable for working in dry and low temperature. To ensure long-term stable operation of LEDs under harsh outdoor conditions, the waterproof structure design of lamps is extremely critical.
At present, the waterproof technology of lamps and lanterns is mainly divided into two directions: structural waterproofing and material waterproofing. The two waterproof designs are suitable for different product routes and have their own advantages. Today we first introduce structural waterproofing.
1. Ultraviolet Rays
Ultraviolet rays have a damaging effect on wire insulation, protective coating of casings, plastic parts, potting compounds, sealing rubber strips, and adhesives exposed to lamps. After the insulation layer of the wire is aged and cracked, the water vapor will penetrate into the interior of the lamp through the gap of the wire core. After the coating of the shell of the lamp is aged, the coating on the edge of the shell is cracked or peeled off, and gaps will appear. As the plastic casing ages, it will deform and crack. The aging of the electronic potting colloid will cause cracking. These are the damage of UV light to the waterproof ability of lamps. 2. High and Low Temperature
The outdoor temperature varies greatly every day. In summer, the surface temperature of lamps can rise to 50-60 ℃ during the day, and drop to 10-20 qC at night. In winter, the temperature can drop to minus zero, and the temperature difference throughout the year changes even more. In the high temperature environment of summer, the material of outdoor lamps accelerates aging and deformation. When the temperature drops below freezing, plastic parts become brittle, or crack under the pressure of ice and snow.
3. Thermal Expansion and Contraction
The thermal expansion and contraction of the lamp housing: the change of temperature causes the thermal expansion and contraction of the lamp. The linear expansion coefficients of different materials (such as glass and aluminum profiles) are different, and the two materials will shift at the joint. The process of thermal expansion and contraction is repeated continuously, and the relative displacement is also repeated, which greatly damages the air tightness of the lamps. The internal air expands and contracts with heat: condensation of water droplets on the glass of buried lamps can often be observed on the ground of the square, and how do the water droplets penetrate into the lamps filled with potting glue? This is the result of respiration during thermal expansion and contraction. For example, when the temperature drops from 60°C to 10°C, the change in air pressure inside 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 interior of the lamp body through the tiny gaps in the material of the lamp body, and then encounters the lower temperature lamp shell, where it condenses into water droplets and gathers. After the temperature is lowered, under the action of positive pressure, the air is discharged from the lamp body, but the water droplets are still attached to the lamp body. The breathing process of temperature changes is repeated every day, and more and more water accumulates inside the lamps. The physical changes of thermal expansion and cold contraction make the design of waterproof and airtightness of outdoor LED lamps a complex system engineering. The following is an analysis of the technical characteristics of the two lighting waterproof systems in order to understand their advantages and disadvantages.
4. About Structural Waterproofing
Lamps based on structural waterproof design need to be closely matched with silicone seals for waterproofing. The shell structure is relatively precise and complex, and is usually suitable for lamps with larger sizes, such as strip floodlights, square and round floodlights, and other medium and high power. lamps. Structural waterproof lamps are only assembled by pure mechanical structure. The tools are simple to use, the assembly process and process are few, the assembly cycle is short, and the repair on the production line is convenient and fast. After the lamps have passed the electrical performance and waterproof tests, they can be packaged and shipped, which is suitable for projects with short supply cycles. However, lamps with structural waterproof design have higher machining requirements, and the dimensions of each component must be precisely matched. Only suitable materials and structures can ensure its waterproof performance. The following design points are as follows.
(1) Design the silicone waterproof ring, select the material with appropriate hardness, design the appropriate pressure, and its cross-sectional shape is also very critical. The cable entry line is the channel for water seepage. It is necessary to choose a waterproof wire, and use a strong waterproof cable gland (PG head) to prevent water vapor from penetrating through the gap of the cable core, but only if the wire insulation layer is strongly squeezed on the PG head for a long time. Press down without aging and cracking. (2) At room temperature, the linear expansion coefficient of glass is about 7.2×10~m/(m·K), and that of aluminum alloy is about 23.2×10-m/(m·K), and the difference between the two is large. When the outer size of the lamp is larger, it must be carefully considered. Assuming that the length of the lamp is 1 000 mm, the housing temperature during the day is 60 °C, the temperature drops to 10 °C during rain or at night, and the temperature drops by 50 °C, the glass and aluminum profiles will 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 repetitive displacement process, which affects the air tightness. 
(3) Many medium and high-power outdoor LED lamps can be installed with waterproof and breathable valves (respirator) to use the waterproof and breathable function of molecular sieves in the respirator to balance the air pressure inside and outside the lamps, eliminate negative pressure, prevent water vapor, and ensure the interior of the lamps is dry. This cost-effective waterproof device can improve the waterproof capability of the original structural design. However, the respirator is not suitable for lamps such as underground lamps and underwater lamps that are often soaked in water. The long-term stability of the waterproof structure of the lamp is closely related to its design, the performance of the selected lamp material, the processing accuracy, and the assembly technology. If the weak link is deformed and seeps water, it will cause irreversible damage to the LED 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 waterproof technology.
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