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These tubes are made for use in " bug zapper" insect traps, and are identified by the industry designation "BL". 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.
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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.