Black Light (BL): emit some visible light as well as ultraviolrt radiation.

Blue Black Light (BLB): are made with a special dark-blue filter glass bulb that absorbs practically all the visible light, yet freely transmits the ultraviolet radiation.

Dramatic lighting effects are achieved with ultraviolet radiation particularly when used with fluorescent inks. These effects find application in signs and posters, to check protective coatings, inspection of hydraulic systems for leaks or inspecting metal castings. A popular application is attracting night flying insects into traps.
These lamps are not intended and should not be used for diagnostic, therapeutic, or cosmetic purposes. The fluorescent blacklight lamps are a source of ultra violet light. Incandescent blacklight lamps are not a source of ultra violet light.