When it comes to explosion-proof lighting for hazardous locations, one of the most frequent questions from clients is whether to choose a tempered glass or a polycarbonate (PC) lens cover. Common settings include offshore platforms, cleaning areas in chemical plants, wastewater treatment facilities, food processing workshops, and gas stations. These environments are typically damp and carry risks of fire or explosion; any failure of the lens cover could lead to issues ranging from water ingress and short circuits to the compromise of the fixture's explosion-proof integrity.
There is no single "correct" answer, as both materials have their own distinct advantages and limitations. Below, we break down several key factors to help you determine which material is best suited for your specific operating conditions.
Challenges for Lens Covers in Damp, Hazardous Locations
In such environments, a lens cover must withstand several simultaneous challenges:
Moisture and Washdowns: High-pressure water jet cleaning, condensation, and exposure to rain require the lens cover to maintain a watertight seal with the gasket over the long term.
Thermal Cycling: The heat generated when the light is on, combined with sudden exposure to cold water, creates thermal shock.
Corrosive Agents: Salt spray, acidic or alkaline vapors, and solvent fumes can gradually erode the material's surface.
Mechanical Impact: Accidental bumps during maintenance, flying debris, or contact with tools are often unavoidable.
Explosion-Proof Requirements: The lens cover must not be the weakest point of the fixture; it must not shatter in a way that could ignite the surrounding atmosphere.
The following comparison of the two materials is based on these criteria.
Tempered Glass: Strengths and Weaknesses
Strengths
Excellent chemical stability: It is highly resistant to most acids, bases, solvents, and salt spray, and will not become brittle or develop surface blemishes (clouding/discoloration) due to long-term exposure to chemicals.
High surface hardness: It is resistant to scratching from cleaning tools, maintains high light transmission over time, and does not yellow even after years of use. It offers a wide temperature tolerance range, meaning it is unlikely to deform or age even when placed near high-power light sources.
It is unaffected by ultraviolet (UV) radiation; unlike plastic, it will not yellow or become chalky after long-term outdoor use.
Drawbacks
Its impact resistance is inferior to that of polycarbonate (PC). If struck forcefully by a sharp object, tempered glass may shatter completely rather than simply developing a crack.
It is sensitive to drastic temperature changes. If exposed to cold water while at a high temperature-especially if there are tiny nicks along its edges-it risks shattering.
Its significant weight places higher demands on the mounting structures and fixation methods used for large-sized light covers.
Polycarbonate (PC): Strengths and Drawbacks
Strengths
It boasts exceptional impact resistance-typically an order of magnitude higher than glass of the same thickness. Upon impact, it generally deforms or cracks rather than shattering into flying shards.
It is lightweight, making transportation, installation, and maintenance at heights much easier.
It offers high design flexibility, allowing for complex, non-standard shapes; its ability to be molded as a single, integrated piece also helps minimize seams.
It is resistant to thermal shock; splashing cold water on it is unlikely to cause it to shatter.
Drawbacks
Its surface is relatively soft and prone to scratching, which can reduce light transmission over time.
Long-term exposure to UV radiation causes it to yellow and become brittle; for outdoor applications, one must select grades that have been treated for UV resistance.
It is intolerant to certain chemicals-such as specific solvents, amines, and strong alkalis-which can cause stress cracking upon contact; this is a critical consideration for chemical processing environments.
When subjected to high-temperature environments for extended periods, it tends to age and deform more quickly than glass.
The Impact on Sealing and Explosion-Proof Certification
The material chosen for a light cover affects not only its durability but also the sealing integrity and certification of the entire lighting fixture.
Differences in thermal expansion: The coefficient of thermal expansion for glass is relatively close to that of metal housings, ensuring a stable compression state for sealing gaskets. Polycarbonate has a higher coefficient of thermal expansion; as temperatures fluctuate, the compression of the sealing gasket will vary, requiring designers to incorporate compensation measures. Flameproof (Ex d): The enclosure must be capable of withstanding internal explosion pressure. Transparent components are typically made of tempered glass, which has undergone rigorous pressure and impact testing.
Increased Safety (Ex e), Dust Ignition-Proof, etc.: Many products in these categories utilize polycarbonate (PC) light covers. Whether such a material is permissible depends entirely on the specific explosion-proof certificate and the associated testing conditions for that model.
When selecting equipment, always refer directly to the product's explosion-proof certificate and technical documentation; do not rely on assumptions based solely on the material type.
Selection Guide for Various Environments
Environment Recommended Material Reason
Chemical processing areas; frequent exposure to solvents Tempered glass Superior chemical stability
Offshore platforms; salt-spray environments Tempered glass Corrosion-resistant; resistant to yellowing
Food processing facilities with frequent high-pressure water washdowns Depends on specific conditions Requires assessment of washdown water temperature and impact risks
Passageways prone to accidental impact by personnel or materials Polycarbonate High impact resistance; does not shatter into dangerous fragments
High-mounted locations with difficult access for maintenance Polycarbonate Lightweight; reduces installation burden and risks associated with falling objects
Areas with high-temperature light sources or proximity to heat sources Tempered glass Better thermal stability
In operating environments characterized by both "severe corrosion" and "high impact," consider using glass combined with a protective guard, rather than forcing a choice between one material or the other.
Routine Maintenance and Replacement Cycles
Tempered glass: Inspect the edges for chips or cracks, and check the sealing gaskets for signs of aging. While minor surface scratches are generally acceptable, the glass must be replaced immediately if any cracks appear.
Polycarbonate: Monitor for yellowing, clouding (fogging), or the development of fine "crazing" (micro-cracks). Avoid using cleaning agents that contain alcohol or strong solvents, as these can induce cracking.
General Note: Regardless of the material, the inspection of sealing gaskets and fasteners should take precedence over the inspection of the light cover itself; in humid environments, water ingress typically begins at the seal points.
Summary
Tempered glass offers excellent resistance to corrosion, heat, and scratching, and it does not age easily. It is well-suited for environments with high chemical or environmental stress, such as chemical plants, offshore facilities, or high-temperature areas. However, be aware that it is vulnerable to strong impacts and rapid temperature changes (thermal shock). Polycarbonate offers the advantages of high impact resistance, lightweight construction, and excellent thermal shock resistance, making it well-suited for areas with high human activity and a significant risk of mechanical impact. However, considerations such as UV-induced aging, surface scratching, and chemical compatibility must be taken into account.
Explosion-proof certification and sealing integrity are critical; the final material selection must align with the specific certifications and operational conditions applicable to the chosen model.
In short: If corrosion and high temperatures are the primary concerns, opt for tempered glass; if impact resistance and ease of installation are the priorities, choose polycarbonate.
Need help selecting the right lens/cover for your project?
If you are specifying equipment for a hazardous, damp environment and are unsure which material to choose, please provide us with details regarding your operating environment-such as the type of substances present, temperature range, required explosion-proof rating, cleaning/wash-down methods, and installation height. Our engineering team will recommend a lighting solution tailored to your specific conditions and can provide samples and technical specifications for both tempered glass and polycarbonate covers. Please feel free to leave a message or submit an inquiry; we will respond as soon as possible.
Our address
No. 5-3 Niujiao Road, Yanchuan Community, Yanluo Subdistrict, Bao'an District, Shenzhen
bwzm18@ledbenweilighting.com
