Fluorescent Black Light

Fluorescent black lights are typically made in the same fashion as normal fluorescent lights except that only one phosphor is used and the normally clear glass envelope of the bulb may be replaced by a deep-bluish-purple glass called Wood's glass, a nickel-oxide-doped glass, which blocks almost all visible light above 400 nanometers. The color of such lamps is often referred to in the trade as "black light blue" or "BLB."