English: Spectrum of light from a fluorescent black light with peaks labelled. The spectrum was taken with an Ocean Optics HR2000 spectrometer . The spectrometer used appears to be about ~.3 to .8 nm off, judging from the location of known peaks. Fluorescent black lights are usually made the same way as regular Wikipedia:fluorescent lamps except the clear glass used in normal fluorescent lights is replaced with "Wood's glass", which is a glass that has been doped with nickel oxide, making it a deep blue/purple color and blocking virtually all visible light above ~400 nm. Also, the phosphor used on the inner surface of the tube differs from the typical multi phosphor blend used in normal fluorescent lights to produce visible light and in black lights is either europium doped strontium fluoroborate or europium doped strontium tetraborate to produce a peak near 370nm, as in this lamp, or a lead doped barium silicate to produce a peak near 351 nanometers. The phosphor fluoresces due to irradiation by short-wave ultraviolet light (UV-C) produced by mercury vapor in the tube. A small amount of the violet light produced by the 404 nm mercury spectral line leaks through the glass filter, causing the second small peak at 404 nm. More info:.