7 Essential Waterproofing Tips for LED Outdoor Lighting Fixtures!

Outdoor lighting fixtures are exposed to long-term tests of ice, snow, scorching sun, wind, rain, thunder and lightning, and their cost is relatively high. As they are installed on exterior walls and difficult to disassemble and repair, they must meet the requirement of long-term stable operation. However, LEDs are delicate semiconductor components; if damp, chip moisture absorption will occur, damaging LEDs, PCBs and other components. Therefore, LEDs work optimally in dry and low-temperature environments. To ensure LEDs operate stably for a long time under harsh outdoor conditions, the waterproof structural design of fixtures is extremely critical.
At present, fixture waterproofing technologies mainly fall into two categories: structural waterproofing and material waterproofing. Structural waterproofing means the product inherently achieves waterproof performance after assembly of all structural components. Material waterproofing refers to reserving spaces in product design for potting adhesive to seal electrical components, with waterproofing realized via adhesive materials during assembly. These two waterproofing designs apply to different product routes and each has its own advantages.
Factors Affecting Fixture Waterproof Performance
Ultraviolet (UV) RaysUV rays damage the insulation layer of exposed wires, shell protective coatings, plastic parts, potting adhesives, sealing rings/strips, and adhesives of fixtures.Aged and cracked wire insulation allows moisture to seep into fixtures through gaps in wire cores. Aging fixture shell coatings cause cracking or peeling at edges, creating gaps. Aged plastic shells deform and crack. Aged electronic potting adhesives crack. Aged and deformed sealing rings/strips lead to gaps. Reduced adhesion of structural adhesives also results in gaps. All these are damages of UV rays to fixture waterproofing capability.
High and Low TemperaturesOutdoor temperatures vary drastically daily: fixture surface temperature can rise to 50～60℃ on summer days and drop to 10～20℃ at night; in winter snowy days, temperatures can fall below zero, with greater annual temperature differences. High summer temperatures accelerate material aging and deformation of outdoor fixtures. In subzero temperatures, plastic parts become brittle and may crack under ice and snow pressure.
Thermal Expansion and Contraction
Fixture Shell Thermal Expansion & Contraction: Temperature changes cause fixtures to expand and contract. Different materials (e.g., glass and aluminum profiles) have different linear expansion coefficients, leading to displacement at their joints. Repeated expansion and contraction cause repeated relative displacement, severely damaging fixture airtightness.
Internal Air Thermal Expansion & Contraction: Condensation droplets are often seen on the glass of in-ground lights in square grounds. How do droplets penetrate fixtures fully filled with potting adhesive? This is the result of breathing effect caused by thermal expansion and contraction.
For example, when temperature drops from 60℃ to 10℃, the internal pressure change of the fixture is about 1 - (273+60)K/(273+10)K = -0.18 atm = -1.86 m water column. Under high negative pressure, humid air seeps into the fixture through tiny gaps in the housing, condenses into droplets on the cooler inner shell and accumulates. When temperature rises, air is expelled under positive pressure, but droplets remain inside. This daily breathing cycle with temperature changes leads to increasing internal water accumulation.
The physical changes of thermal expansion and contraction make the waterproof and airtight design of outdoor LED fixtures a sophisticated systematic project. Below is an analysis of the technical characteristics of the two waterproofing systems to clarify their advantages and disadvantages.
Structural Waterproofing
Fixtures designed with structural waterproofing rely on tightly fitted silicone sealing rings for waterproofing, featuring precise and complex shell structures. They are usually suitable for large-size fixtures, such as linear floodlights, square and round projectors, and other medium-to-high power fixtures.
Structural waterproof fixtures only require pure mechanical assembly with simple tools, fewer assembly processes and shorter total assembly cycles, enabling quick rework on production lines. Once passing electrical performance and waterproof tests, they can be packaged and delivered, making them ideal for projects with short delivery cycles.
However, structural waterproof fixtures demand high precision machining and tight dimensional tolerance of all components. Only appropriate materials and structures can guarantee waterproof performance, with the following key design points:
Design silicone waterproof rings with suitable hardness, pressure and cross-sectional shape (critical factor).
Cable entries are water seepage channels; waterproof wires must be used, and robust cable glands (PG glands) are required to prevent moisture seepage through wire core gaps. The prerequisite is that wire insulation does not age or crack under long-term high-pressure extrusion of PG glands.
At room temperature, the linear expansion coefficient of glass is about 7.2×10⁻⁶ m/(m·K), and that of aluminum alloy is about 23.2×10⁻⁶ m/(m·K), showing a large difference, which must be carefully considered for large-size fixtures. For example, a 1000 mm long fixture: when shell temperature drops from 60℃ (daytime) to 10℃ (rainy days or nights), a 50℃ decrease causes glass to shrink by 0.36 mm and aluminum profile by 1.16 mm, resulting in a relative displacement of 0.8 mm. Repeated stretching of sealing components during such displacement impairs airtightness.
Many medium-to-high power outdoor LED fixtures can be equipped with waterproof breathable valves (respirators). Utilizing the waterproof and breathable function of molecular sieves in respirators, they balance internal and external pressure, eliminate negative pressure, prevent moisture inhalation and keep fixtures dry. This cost-effective waterproof component enhances the waterproof capability of original structural designs but is not suitable for submerged fixtures like in-ground lights and underwater lights.
The long-term stability of structural waterproofing is closely related to design, material performance, machining precision and assembly technology. Deformation and water seepage at weak points cause irreversible damage to LEDs and electronic components. Such issues are hard to predict during factory inspection and occur suddenly, so continuous improvement of waterproofing technology is needed to enhance the reliability of structural waterproof fixtures.
Material WaterproofingFixtures designed with material waterproofing use potting adhesive for insulation and waterproofing, and sealant to bond and seal joints between structural components, fully sealing electrical parts to achieve waterproofing for outdoor fixtures.
Potting AdhesivesWith the development of waterproof materials, various types and brands of special potting adhesives for fixtures emerge continuously, such as modified epoxy resin, modified polyurethane resin and modified silicone resin. Different chemical formulas result in varied physical and chemical properties including elasticity, molecular structure stability, adhesion, UV resistance, heat resistance, low-temperature resistance, hydrophobicity and insulation performance.
Elasticity: Soft adhesives with low elastic modulus offer better adaptability; modified silicone resin has the smallest elastic modulus.
Molecular structure stability: Stable chemical structure without aging or cracking under long-term UV, air and temperature exposure; modified silicone resin performs best.
Adhesion: Strong adhesion prevents peeling; modified epoxy resin has the strongest adhesion but poor chemical stability, prone to aging and cracking.
Hydrophobicity: Indicates adhesive's water resistance; modified silicone resin has good hydrophobicity.
Insulation: Related to product safety; all the above special potting adhesives meet requirements.
Comprehensively, modified silicone material exhibits the best overall physical and chemical performance.
Sealing Adhesives
Sealants are usually tube-packed for convenient application, mainly used for bonding and sealing wire ends and joints between shell structural components. Most are one-component formulas that react with air moisture and cure naturally at room temperature.
Critical Note: Some fixture manufacturers use neutral curtain wall adhesives for construction instead of professional electronic sealants, which easily decompose harmful substances and damage fixtures.
During curing, certain potting and sealing adhesives release small amounts of chemical liquids or gases. For example, decomposition products near lamp beads damage phosphors (causing color temperature drift), corrode LED chips, or produce substances that react with transparent PC plastic and damage its structure. These are potential hazards of adhesive application; designers must fully understand their chemical and physical properties from manufacturers and conduct verification tests.
Sealants for bonding and sealing fixture shells are most affected by thermal expansion and contraction, especially for large fixtures with distinct linear expansion coefficients of different materials. Repeated stretching easily causes cracks. Therefore, the waterproofing capability of material waterproofing design mainly depends on circuit board potting.
Material waterproofing involves a long production process: one potting and curing cycle takes 24 hours; complex product designs may even require 2-3 cycles, leading to long delivery times, extensive occupation of production space and messy production environments. Reworking after adhesive curing is cumbersome.
Material waterproof fixtures do not require high-precision structural design, only reserved potting areas to prevent liquid leakage, with intuitive waterproof performance. Thus, material waterproofing is suitable for small outdoor fixtures and indoor moisture-proof fixtures, and widely applied in low-end and cheap universal-mold products such as flexible light strips, small linear lights and in-ground lights.

Shanghai Shenchang Lighting Electrical Appliance Co., Ltd. was founded in 1995, a technology-oriented enterprise integrating R&D, manufacturing, sales and project implementation. In recent years, responding to the national energy conservation and emission reduction strategy, the company has built on its traditional fixture production foundation to develop green lighting. It has established production bases in Shanghai, Shenzhen and Ninghai, developing and producing innovative, high-efficiency, energy-saving and long-life Shenchang brand LED lighting series products with independent intellectual property rights.