PC Lighting Profile Design Guide

When PC is the right call

• The fixture must survive impact – industrial, transport, public-space or vandal-resistant luminaires.
• Ambient or local temperature is high, near high-power LED boards or in enclosed housings.
• A flame rating (UL94 V-2, V-0 or 5VA) is part of the specification.
• The profile is structural and carries fixing loads.
• The application is industrial, troffer or any environment where the cover is struck or cleaned aggressively.

Grade selection

Additives change more than compliance. Flame retardants typically reduce transmission slightly and raise cost; UV stabilisers are essential outdoors but unnecessary indoors; diffusion masterbatch sets haze and directly reduces transmission. State the optical target alongside the grade so the two are balanced rather than traded away. Full material data: polycarbonate.

Wall thickness and section design

1.5-3.0 mm is typical for PC lighting sections, with about 0.8-1.0 mm the practical floor for short runs. PC is strong enough that wall thickness is usually driven by stiffness, extrusion stability and optics rather than by strength. Keep adjacent walls within about 2:1 and core out thick sections instead of leaving them solid – PC is prone to sink marks and vacuum voids in thick sections.

Radii and notch sensitivity

PC is tough but notch-sensitive: a sharp corner concentrates stress and turns a tough material into a brittle one. Use an internal radius of at least half the wall thickness everywhere, and more at any feature that flexes. The root of a snap-fit leg is the classic failure point – radius it generously and check the deflection strain stays within the grade’s limit.

Snap-fits and living features

• Design the leg to deflect over a length, not at a point – a long tapered leg strains far less than a short stubby one.
• Keep deflection strain below roughly the grade’s allowable limit; for PC lighting grades this is typically a small single-digit percentage at room temperature.
• Provide a lead-in chamfer so assembly does not scrape the mating surface.
• Avoid designing a snap-fit that must be released repeatedly – PC creep and stress relaxation will reduce retention over time.

Process sensitivities that affect the design

Moisture

PC must be dried thoroughly before melting, typically to around 0.02% moisture or lower. Under-dried PC hydrolyses in the barrel: molecular weight drops, the profile becomes brittle, and silver streaks appear. This is a processing discipline issue, but it shows up as a field failure attributed to material quality – so buy from a supplier who documents drying.

Internal stress and ESC

PC retains internal stress from cooling and is vulnerable to environmental stress cracking when exposed to certain chemicals – some adhesives, gasket plasticisers, cleaning agents and printing inks. Tell your supplier which chemicals the profile will see in assembly and service. Solutions include grade selection, annealing, or specifying a compatible adhesive.

Colour consistency

PC runs at higher melt temperature than PMMA, so shade drift between batches is a real risk on colour-matched work. A signed-off physical standard plus recorded line parameters is the control. Ask for it if the profile is visible.

Optical design in PC

Standard PC transmits roughly 88-90%. Diffusion masterbatch reduces that further, so the optical budget has to be designed: LED flux, transmission, wall thickness and target output are one equation. For a diffuser profile, the thinnest wall that hides the hotspots is usually the right answer. For a lens profile, PC’s refractive index and the machined die land define the beam.

Co-extrusion with PC

PC co-extrudes well with a flexible sealing lip and with opaque housing sections, giving a one-part alternative to an assembly. It also pairs with a PMMA optical window where you want PC’s strength in the body and PMMA’s transmission in the optics. Two-material dies need compatible melt behaviour – decide before tooling. See manufacturing.

PC design checklist

1. Grade chosen for UV, FR and diffusion requirement – not just “PC”.
2. Wall thickness uniform, 1.5-3.0 mm typical, thick sections cored out.
3. All internal corners radiused; snap-fit roots generous.
4. Snap-fit deflection strain within grade limit.
5. Chemical exposures listed, so ESC risk is addressed at grade selection.
6. Colour standard defined – RAL, Pantone or physical sample.
7. Optical target stated: transmission %, haze %, or beam distribution.
8. Critical dimensions marked; the rest at general tolerance.

Send the drawing and application for a feasibility review: PC lighting profiles or request a quote.