Black Light. What is it? It is a portion of the Ultra-Violet Spectrum that is invisible to our eyes. We cannot distinguish it. However, when this radiation impinges on certain materials visible light is emitted and this is known as “fluorescence.” Fluorescence is visible to the human eye, in that it makes an object appear to “glow in the dark.” There are several sources of ultra-violet light. These sources are: the sun, carbon arcs, mercury arcs, and black lights. In most cases, the production of ultra-violet light creates a reasonable amount of heat. Many materials exhibit the peculiar characteristic of giving off light or radiant energy when ultra-violet light is allowed to fall upon them.
This is called luminescence. In most cases, the wave length of the light radiated is longer than that of the ultra-violet excitation but a few 
exceptions have been found. The quantum theory attempts to explain this property by contending that a certain outside excitation causes an electron to jump from one orbit to another. It is then in an unstable environment causing it to fall back into its original orbit. This process releases energy, and if it is in the visible part of the spectrum, we have a transient light phenomenon. Ultra-violet light is an exciting agent which causes luminescence to occur. There are many materials which exhibit fluorescent characteristics. Many of which are even organic. Teeth, eyes, some portions of the skin, and even blood exhibit fluorescent qualities. Naturally occurring minerals such as: agate, calcite, chalcedony, curtisite, fluorite, gypsum, hackmanite, halite, opal scheelite, and willemite, also have similar characteristics. These materials can be used in industries. The radiance of ultraviolet light is measured in units called “Angstrom.”
The intensity of ultraviolet fluorescence is the greatest between the 5000 and 6000 range. This being the range between the green and yellow hues. Ultra violet light is not readily visible. It is not visible because certain materials reflect it. Ultra-violet light is made visible due to the fact that it causes a reaction at the atomic level. When it strikes the atom, some of the electrons are sent into other orbits. This then creates an unstable situation which causes the electron to fall back into its place. This process produces energy, and this is what is seen. This discharge of energy is what creates the “glow” that is seen. Ultraviolet light causes the atom to lose a subatomic particle then regain it, and give off energy in the form of visible light. This is just amazing.
