the black light is a light ultraviolet produced with a small amount of visible light. When violet light falls on phosphorescent compounds, such as the mineral calcite or the sulphide in zinc, she is absorbed. After interruption of the light stimulus, the phosphorescent materials emitslowly part of the energy absorbed in the form of lightvisible, displaying a shineweak during longbreaks of time.
Phosphorescence is a particular type of fluorescence. In these optical phenomena, there is the absorption of ultraviolet radiation and the slow emission of visible light.
Most of the electromagnetic waves produced by fluorescent lamps are ultraviolet rays, formed by acceleration on one steam of gas inside. This radiation is absorbed by a thin layer in White powder composed of salts of phosphor, which produces visible light through phosphorescence.
When the white layer is removed from the fluorescent lamps, the ultraviolet rays can propagate outward of the lamp bulb. White clothes, as well as other phosphorescent compounds, fulfill the role of
re-emit this energy in the form of visible light. Some detergents used to lighten clothes have substances in their composition that are excited in the presence of ultraviolet rays and emit White light, causing the object to appear even brighter.There are several uses for black light. Fabrics like bones and nails, Besides sweat and Spittle,contains phosphorescent compounds that emit a small amount of lightvisible when they are exposed to rays UV. This is why the use of black light is so common in criminal investigations.
By Rafael Hellerbrock
Graduated in Physics
Source: Brazil School - https://brasilescola.uol.com.br/o-que-e/fisica/o-que-e-luz-negra.htm