Hi-vis garments are class-rated for the conditions they're visible in — and a day-rated vest on a night shift is compliance on paper only.
The three classes
- Class D (day) — fluorescent background material only; visible in daylight.
- Class N (night) — retroreflective tape that returns headlight beams; the fluoro background does nothing after dark.
- Class D/N — both; the default for civil and roadside crews.
Fluorescent fabric needs UV light to glow — that's why day-only hi-vis disappears under floodlights.
When to retire a garment
Wash-faded fabric and cracked tape both void the rating. If the tape doesn't light up in a photo taken with flash, the garment is done.