UV (ultra violet) is a portion
of the electromagnetic spectrum just past violet which is at the short
wavelength end of visible light as seen by the human eye. UV can not be
seen by the human eye, but when it falls on certain materials it may cause
them to become fluorescent (ie. glow) and reflect visible light back to
There are 3 different
types of UV light
UVA (315-400nm) is commonly known as "black light". This is fairly
safe UV light.
UVB (280-315nm) is dangerous with overdose and will cause the skin
to burn and blister.
UVC (100-280nm) is very dangerous and is mostly blocked from the sun
by the earth's atmosphere .
Fluorescent lighting tubes generate
UVA and the powder on the inside surface of the glass tube becomes fluorescent
and glows to produce a very efficient form of lighting.
Fluorescent tubes in dance clubs
have a special glass coating so only the safe part of UVA "black light"
is transmitted into the room, making only some items become fluorescent
and glow extra brightly.