what is black light used for?
A black light is a source of electromagnetic radiation that emits near-ultraviolet light, usually in the 350-375 nanometer wavelength range. This range is just slightly below the 400nm that human eyes can detect. When this light is reflected off certain materials, it looses energy and its wavelength expands to over 400nm. The reflected light is then visible to human eyes, and the illuminated objects appear to glow.