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These tubes are made for use in " bug zapper" insect traps, and are identified by the industry designation "BL".
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This stands for "blacklight blue".Ī second type of lamp produces ultraviolet but does not have the filter material, so it produces more visible light and has a blue color when operating. Blacklight lamps which have this filter have a lighting industry designation that includes the letters "BLB". One type of lamp has a violet filter material, either on the bulb or in a separate glass filter in the lamp housing, which blocks most visible light and allows through UV, so the lamp has a dim violet glow when operating. The violet glow of a black light is not the UV light itself, but visible light that escapes being filtered out by the filter material in the glass envelope.Ī blacklight, also referred to as a UV-A light, Wood's lamp, or ultraviolet light, is a lamp that emits long-wave ( UV-A) ultraviolet light and very little visible light.