PC vs PMMA for LED Light Covers

The deciding questions

1. Does the fixture need an impact rating or vandal resistance? If yes – PC.
2. Does it need a UL94 flame rating? If yes – PC, in most cases.
3. Is the cover outdoors or daylight-exposed? If yes – PMMA, or UV-stabilised PC.
4. Is maximum light output the priority with no impact or flame requirement? If yes – PMMA.

In practice the first two questions decide most commercial and industrial fixtures. Where neither applies, PMMA usually wins on output and appearance.

Property comparison for covers

Where PC covers are specified

• Industrial and low-bay fixtures where the cover is struck by tools or debris.
• Troffer and recessed commercial fixtures with a flame-rating requirement.
• Public-space, transport and vandal-resistant luminaires.
• Enclosed high-power fixtures where cover temperature is high.
• Any fixture that must carry an IK rating.

See PC light covers.

Where PMMA covers are specified

• Architectural and decorative fixtures where clarity and long-term colour stability are visible.
• Office and commercial interiors with no impact requirement.
• Signage, edge-lit and light-guide applications.
• Fixtures where the cover is cleaned frequently and scratch resistance matters.

See PMMA light covers.

Output: what the material actually costs you

The transmission difference between PC and PMMA is a few percentage points, and in a diffusing cover the haze package usually dominates the loss rather than the base polymer. The practical approach is to specify the cover by its optical target – transmission and hotspot hiding at the intended viewing angles – and let the material follow from the compliance requirement. Where PC is mandatory, recover the output by designing more standoff rather than by thinning the wall below the impact requirement.

Long-term appearance

This is the difference that shows up in year three. Unstabilised PC yellows under UV and heat, shifting the apparent colour temperature of the fixture – highly visible where fixtures are compared side by side on a facade or a long office run. PMMA holds its transmission and colour far better. Where PC is required for impact, specify a UV-stabilised lighting grade; it is a small premium against a visible complaint.

Handling and cleaning

PMMA is harder and resists scratching better; PC marks more readily in handling and cleaning. Where a PC cover is in a visible location, consider a fine texture – it hides handling marks and costs nothing in the extrusion. Also specify which cleaning agents the cover will see: both materials craze in contact with certain solvents and adhesives.

Using both

A very common construction is a PC or PMMA housing profile co-extruded with an optical window in the other material, giving PC’s strength where it is needed and PMMA’s optics where light leaves the fixture. It requires compatible grades and a two-stream die, so it is decided at drawing stage. See manufacturing.

Full comparison: PC vs PMMA lighting profiles. Material pages: polycarbonate, PMMA / acrylic. Or send the drawing – request a quote.