File:Portable black light fluorescent lamp.jpg

English: A portable "black light" ultraviolet fluorescent lamp, sold as a pet urine detector, to make urine stains on carpet and furniture visible by its fluorescence. It uses an F8T5/BLB 11 inch 8 watt black light UV tube, with a solid state ballast, powered by eight AA size batteries. It radiates "long-wave" or UVA ultraviolet radiation, with a wavelength in the range 350 to 370 nm, which is not dangerous to eyes or skin. The purple glow of the tube is not the ultraviolet radiation itself, which is invisible, but a small amount of visible purple light from mercury's 404 nm spectral line leaking through the blue filtering glass of the tube, which is designed to pass ultraviolet light.