except that a phosphor that emits UVA light instead of visible white light is used. The type most commonly used for black lights, designated blacklight blue or "BLB" by the industry, has a dark blue filter coating on the tube, which filters out most visible light, so that fluorescence effects can be observed. These tubes have a dim violet glow when operating. They should not be confused with "blacklight" or "BL" tubes, which have no filter coating, and have a brighter blue color.