PC, PMMA, Glass--How to choose for lighting?

Have you ever encountered this situation? After two or three years of outdoor use, the clear cover of a light fixture has yellowed, looking as if it's been covered in a fog. The light is still on, but the light doesn't shine through, and the illuminance on the ground has dropped significantly, which leads to constant complaints from the customers.

Where does the problem lie? Most likely, the wrong lens material was chosen.

Today, we'll break down the three most common lens materials: PC, PMMA (acrylic), and glass.

I. Three Materials, Three Destinies

PC (Polycarbonate) — The King of Outdoor Materials

PC is commonly known as “bulletproof plastic,” and for good reason. Its key features include impact resistance, heat resistance, and UV resistance.

Impact Resistance: If struck with a hammer, it may dent but will not shatter.

Heat Resistance: It can withstand operating temperatures of 120°C or higher.

UV Resistance: When treated with UV-blocking additives, it remains yellow-free for 5–10 years of outdoor use.

What are the disadvantage? Cost. For lenses of the same specifications, PC is 30%–50% more expensive than acrylic. Additionally, PC has low surface hardness and is prone to scratching, so it is generally not used for exposed surfaces; instead, it is coated or given a frosted finish.

Applications: Outdoor streetlights, wall-washer lights, tunnel lights, high bay lights, stadium lights—anywhere exposed to wind, sun, and rain, PC is the top choice.

PMMA (Acrylic) — The Indoor Champion

Acrylic’s greatest advantage is its high light transmittance. Pure acrylic can achieve a light transmittance of up to 92%, which is slightly higher than that of PC (88%–90%). It is also inexpensive, easy to process, and can be finished with a very smooth surface.

However, acrylic has one disadvantage: it is vulnerable to UV rays.

Ultraviolet rays in sunlight cause the molecular chains of acrylic to break down, resulting in yellowing, brittleness, and cracking. When used outdoors, acrylic will inevitably yellow within one to three years.

Suitable for: Indoor downlights, panel lights, tubes, and display case lighting—in areas not exposed to direct sunlight, acrylic offers the best value for money.

Glass—High-End but Fragile

The advantages of glass is the highest light transmittance (92%–94%), high hardness that resists scratches, heat resistance, and resistance to yellowing.

The disadvantages are that it is heavy, fragile, and expensive. Furthermore, glass is difficult to process, and producing custom-shaped lenses is very costly.

Suitable for: museums, art galleries, high-end commercial lighting, explosion-proof fixtures, and applications requiring extremely high light transmittance. It can be used outdoors, provided the installation location is not prone to being struck.

II. Comparison of Key Metrics

III. How to Choose Lens Materials?

Scenario 1: Outdoor streetlights, wall-washer lights, and floodlights

PC must be used, and it must be UV-resistant PC.

Why? Because these lights are installed outdoors, where they are exposed to direct sunlight, wind, and rain, and may occasionally be struck by flying debris. Acrylic won’t last more than two years, and glass breaks easily. PC is the only material that can withstand outdoor conditions.

Scenario 2: Indoor Downlights, Panel Lights, and Linear Lights

Acrylic is the highest cost effective. Since there is no risk of UV exposure indoors, acrylic provides excellent light transmission, cost-effective, and allowing for high-precision machining, resulting in a uniform light pattern.

However, there is one exception: if the fixtures are installed next to a window where direct sunlight can reach, PC should be used instead. Otherwise, the PMMA will yellow within two years, leading to customer complaints.

Scenario 3: Museums, Art Galleries, and High-End Commercial Spaces

Glass is the top choice. These areas demand extremely high light quality; even a 1% difference in light transmittance can affect the effect when the items are displayed. Furthermore, glass never yellows and will look as good as new even after ten years.

The disadvantages are expensive, heavy, and requires careful installation. Make sure if it is tempered glass in purchasing. When tempered glass breaks, it shatters into small granules, making it safe; ordinary glass, however, breaks into sharp shards that can easily cause injury.

Scenario 4: High-Bay Lights

Consider the installation height and location.

For installations at high place (8 meters or higher) in areas where the lights are unlikely to be struck: PC (polycarbonate) is sufficient and offers good value for money.

For installations at medium or low heights in areas where there is a risk of impact: PC is required for its impact resistance.

For special environments (chemical plants, dusty workshops): Explosion-proof glass may be required; select according to explosion-proof lighting standards.

Scenario 5: Explosion-Proof Lighting Fixtures

Tempered glass must be used. Explosion-proof standards strictly prohibit the use of PC or acrylic. PC may soften at high temperatures, and acrylic is flammable; neither material meets explosion-proof requirements.

When purchasing explosion-proof lighting fixtures, you don’t need to worry about the lens material—it is already specified by the standards. However, you must verify whether the glass is tempered and whether the product has an explosion-proof certification.

IV. Three Essential Questions to Ask When Purchasing

1. “What material is the lens made of? PC or acrylic?”

Don’t ask “Is it anti-glare?”—ask about the material first. If you hear the word “acrylic,” immediately rule it out for outdoor projects.

2. “Does the PC have UV protection?”

Standard PC will yellow over time outdoors, though it takes longer than acrylic. Only PC with UV-resistant additives can last 5–10 years. Ask the supplier for a UV resistance test report (QUV test) to see how many hours it takes to yellow.

3. “Is the glass tempered?”

If you choose glass, make sure to ask if it’s tempered. When tempered glass breaks, it shatters into small granules; ordinary glass breaks into sharp shards, which can easily cause injury.

A quick guide to choosing the right material:

Outdoor use, risk of impact damage, prone to yellowing → PC

Indoor use, looking for value for money, not concerned about sun exposure → Acrylic

High-end, requires high light transmission, demands a premium look and feel, budget is no issue → Glass