Is CR-39 ever acceptable in safety glasses?

Only where the hazard assessment genuinely requires no impact grade beyond S — which is rare in industrial settings. The moment the assessment says F, CR-39 is a non-compliant choice regardless of the frame it sits in. Certus does not dispense CR-39 in safety eyewear at all.

Is polycarbonate optically worse than CR-39?

Its dispersion is higher (Abbe 30 vs 58), which can soften edge-of-lens sharpness at stronger prescriptions. For typical prescriptions the difference is modest, and where optics are critical Trivex offers impact protection with materially better optical quality.

Doesn’t polycarbonate scratch easily?

The substrate is softer than CR-39, so the hard coat does the work — look for the K marking, which certifies resistance to surface damage by fine particles. Every Certus lens ships hard-coated.

What about glass lenses for safety work?

Toughened glass eye protection exists but is heavy and now rare in industrial prescription work; polymer materials dominate because they combine impact absorption with wearable weight.

Do tints or photochromics change the impact rating?

No — the mechanical grade comes from the lens material and its testing, not its colour. Tints, blue-light filters and photochromic options are available on impact-rated materials; the marking still has to show the grade the task requires.

CR-39 vs Polycarbonate Safety Glasses: What's Actually Compliant — Certus

CR-39 clears EN 166 S but cannot achieve the F impact grade most industrial tasks demand. The lens-material decision, with the numbers.

Certus is a UK platform for managing prescription safety eyewear compliance to EN 166, covering hazard assessments, ordering, optician verification and certificate records. Operated by Certus Safety Ltd, registered in England and Wales, company number 17364362.