Outdoor lighting fixtures need to withstand the test of snow, wind, rain, and lightning for a long time, and the cost is relatively high, and because it is difficult to disassemble and repair on the external wall, it must meet the requirements of long-term stable work. LEDs are delicate semiconductor components. If they get damp, they will appear. The chip absorbs moisture and damages LED PCB and other components. Therefore, the LED is suitable to work in a dry and low temperature to ensure that the LED can work stably for a long time under severe outdoor conditions. The design of the waterproof structure of the lamp is extremely important.
At present, the waterproof technology of lamps and lanterns is mainly divided into two directions: structural waterproofing and material waterproofing; the so-called structural waterproofing means that the product has a waterproof function after the various structural components are combined; and the material waterproofing is to leave the potting in the product design. The glue seals the position of the electrical components, and the glue material is used to achieve waterproof during assembly. Two waterproof designs are suitable for different product routes, and each has its own advantages.
Factors affecting the waterproof performance of lamps
A: Ultraviolet Rays
Ultraviolet rays have a destructive effect on the protective coating of the protective coating of the wire insulation layer shell plastic parts that are exposed to 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 lamp shell coating is aged, the coating on the edge of the shell will crack or peel off, and there will be gaps. After the plastic shell is aged, it will deform and crack the electronic potting gel. Aging will produce cracking and aging deformation of the sealing rubber strip, and the adhesive between the structural parts of the gap will be aging, and the gap will also appear after the adhesion is reduced. These are the damage to the waterproof ability of the lamp by ultraviolet rays.
B: High and Low Temperature
The outdoor temperature changes greatly every day. In summer, the surface temperature of the lamps can rise to 50-60 during the day, and drop to 10-20 qC at night. In winter, the temperature can drop to below zero on icy and snowy days, and the temperature difference throughout the year is even greater. Outdoor lamps have a high temperature environment in summer When the temperature drops to below zero, the plastic parts become brittle and may crack under the pressure of ice and snow.
C: Thermal Expansion and Contraction
Thermal expansion and contraction of the lamp shell: The change of temperature causes the lamp to expand and contract. Different materials (such as glass and aluminum) have different linear expansion coefficients. The two materials will shift at the joint. The process of thermal expansion and contraction is repeated continuously. The relative displacement is also repeated continuously, which greatly damages the air tightness of the lamp
The internal air expands with heat and shrinks with cold: the water droplets on the glass of the buried lamp can often be observed on the ground of the square, but 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 to 10, the change in air pressure inside the lamp is approximately: 1-(273+60)K/(273+10)K =-0.18 atm =-1.86 m water column.
The temperature rises. Under the action of huge negative pressure, the air penetrates into the interior of the lamp body through the micro gaps on the lamp body material, and meets the lower temperature lamp shell, condenses into water droplets and gathers after the temperature drops. Under the action of pressure, air is discharged from the lamp body, but the water droplets are still attached to the lamp. The breathing process of repeated temperature changes every day, more and more water accumulates in the lamp.
The physical changes of thermal expansion and contraction make the design of waterproof and air-tightness of outdoor led lamps a complicated system project. The following analyzes the technical characteristics of the two kind lamp waterproof systems in order to understand their advantages and disadvantages.
About Structural Waterproofing
Luminaries based on structural waterproof design need to be closely matched with silicone seals for waterproofing. The shell structure is more sophisticated and complex. It is usually suitable for large-sized lamps, such as strip floodlights, square and round floodlights and other medium and high-power lamps.
Structural waterproof illuminates are only assembled with pure mechanical structure. The tools are simple, the assembly process and process are few, the final assembly cycle is short, and the production line is convenient and quick to repair. The luminary can be packaged and shipped after passing the electrical performance and waterproof test. It is suitable for short delivery cycles project.
However, the structural waterproof design of lamps and lanterns requires high machining, and the size of each component must be precisely matched. Only suitable materials and structures can ensure its waterproof performance. The following design points:
(1) Design silicone waterproof ring: Choose materials with suitable hardness, design suitable pressure, and its cross-sectional shape is also very important. The cable entry line is a water seepage channel. You need to choose a waterproof wire. Use a strong cable waterproof fixing head (PG head) to prevent water vapor from the cable core. Penetration in the gap, but the premise is that the wire insulation layer does not age or crack under the long-term strong extrusion of the PG head.
(2) At room temperature: The linear expansion coefficient of glass is about 7.2×10～m/(m·K), and the aluminum alloy is about 23.2×10 one m/(m·K). The difference between the two is large. When the outer size of the lamp is large, the assumption of the lamp must be considered The length is 1000 mm, the temperature of the shell during the day is 60, the temperature drops to 10 in the rain or the night, and the temperature drops by 50. 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 repeating Pulling repeatedly during sexual displacement affects air tightness.
(3) Many medium and high-power outdoor LED lamps can be installed with waterproof and breathable valves (respirators), which use the waterproof and breathable function of molecular sieve in the respirator to balance the air pressure inside and outside the lamp, eliminate negative pressure, prevent inhalation of water vapor, and ensure that the inside of the lamp is dry. Economical and effective waterproof device can improve the waterproof ability of the original structure design, but the respirator is not suitable for lamps that are often submerged in water such as underground lamps and underwater lamps.
The long-term stability of the waterproof structure of the lamp is closely related to the performance, processing accuracy, assembly technology, etc. of the selected lamp material. If the weak link is deformed and seepage, it will cause irreversible damage to the LED and electronic devices, and this situation will be inspected at the factory The process is difficult to predict and is sudden. Therefore, to improve the reliability of structural waterproof lamps, it is necessary to continue to improve the waterproof technology.
About Material Waterproofing
Lamps with material waterproof design use filling potting glue to insulate and waterproof, use sealant to bond and close the joints between structural parts, so that electrical parts are completely airtight, and achieve the effect of waterproofing outdoor lamps.
A: Potting Glue
With the development of waterproof material technology, various types and brands of special potting glues for lamps and lanterns continue to appear. For example, the chemical formulas of modified epoxy resin modified polyurethane resin modified organic silica gel are different, and the elastic molecular structure of the potting glue is stable. Adhesion resistance, UV resistance, heat resistance, low temperature resistance, water repellent, insulation performance, and other physical and chemical performance indicators vary.
Elasticity: The colloid is soft, and the elastic modulus is small, so the adaptability is better. The elastic modulus of modified silicone is the smallest.
Molecular structure stability: Under the long-term action of UV air and high and low temperature, the chemical structure of the material is stable, and does not age or crack. Among them, modified organic silica gel is the most stable.
Adhesion: If the adhesion is strong, it is not easy to peel off. Among them, the adhesion of modified epoxy resin is the strongest, but the chemical structure is less stable, and it is easy to age and crack.
Hydrophobicity: indicates the ability of the colloid to resist water penetration. The modified organic silica gel has better hydrophobicity.
Insulation: Insulation is related to product safety indicators. The special potting glue of the above several materials is good. The special potting glue of the material is good.
From the comprehensive view of the above physical and chemical properties, modified silicone materials perform best.
The sealant is usually a tubular packaging, suitable for glue construction. It is generally used for bonding and sealing the indirect seam of the wire end shell structure. A commonly used single-component formula. It reacts with air and water vapor at room temperature and solidifies naturally.
Special attention: Some lighting manufacturers use neutral curtain wall glue for construction instead of professional electronic sealant, which easily decomposes harmful substances and damages the lamps.
Certain types of potting and sealants will decompose a small amount of chemical liquids or gases during the solidification process. For example, the colloidal decomposition products next to the lamp beads will damage the fluorescent powder of the lamp beads, resulting in color temperature drift or damage to the LED chip, or It decomposes substances that chemically react with the transparent PC plastic to destroy the structure of the PC, etc. This is a potential hazard in the application of colloids. The colloid manufacturer must fully understand its chemical and physical properties and test and verify it during design.
In the bonding and sealing of the lamp housing structure, the sealant is most affected by thermal expansion and contraction, especially for large lamps. The linear expansion coefficients of different materials are quite different. The thermal expansion and contraction continue to pull and cracks are prone to appear. Therefore, the material is waterproof. The waterproof ability of the circuit board mainly depends on the potting of the circuit board.
The production process of material waterproofing is long. One potting solidification cycle takes 24 hours. Some product designs are more complicated, even requiring 2 to 3 potting cycles. This leads to a long shipping cycle, a large number of production sites, and production environment. It is troublesome to repair the product after the dirty colloid has solidified.
The structural design of material waterproof lamps does not need to be too precise, as long as the design reserves a gel potting area so that the liquid does not leak, and its waterproof performance is very intuitive. Therefore, the material waterproof process is more suitable for small outdoor lamps, and indoor moisture-proof lamps are usually at the low end. And a large number of low-cost public model products are used in a large number of small lamps such as soft lights with small strip lights and buried lights.
Regardless of structural waterproofing or material waterproofing, for the long-term stable and low failure rate of outdoor lamps, it is difficult to achieve extremely high reliability with a single waterproof design, and the potential for water seepage still exists.
Therefore, in the design of high-end outdoor LED lamps, it is recommended to use waterproof technology flexibly, combine the advantages of structural waterproofing and material waterproof technology, and maximize the strengths and avoid weaknesses to ensure the long-term stable operation of the LED circuit. For example, the material waterproof design can add a respirator to eliminate negative pressure and the structure Waterproof design, you can also consider adding potting, double waterproof protection, to improve the stability of outdoor lighting for long-term use, and reduce the failure rate of moisture.
Upward Lighting, founded in 2009, focuses on outdoor landscape lighting projects, customizing various non-standard outdoor led lamp manufacturers, main LED flood lights, LED wall washer lights, LED line lights, LED underwater lights, LED buried Lights, LED explosion-proof lights, etc., provide effect design, installation guidance, all-day technical support, after-sales tracking and other one-stop services.