Photoluminescent fire extinguisher rigid pvc sign, non-adhesive 4″ x 20″ these photoluminescent rigid pvc safety signs absorb and store energy from ambient lighting. Signs are immediately visible in case of black-out. These stiff, smooth signs work great on uneven, rough surfaces, even on brick wall. Install these sturdy, durable rigid glow signs with double-sided tape or liquid adhesive (not included in sign package). 8-hour photometer measurable darkness glow.