Visible Light

All light is composed of electromagnetic waves. When a ray of light is refracted through a prism, the visible components of the light are revealed as a rainbow. The "first" colors--red, orange and yellow--have the longest wavelengths. The "last" colors--blue, indigo and violet--have the shortest wavelengths.

Invisible Light

On either end of the visible spectrum, additional waves of light exist that are invisible to the human eye. Infrared light has a very long wavelength, but gives off relatively small amounts of energy. Ultraviolet light has a shorter wavelength and gives off higher amounts of energy.

Black Lights

Unlike traditional incandescent lightbulbs, "black lights" project only high-energy light from the high end of the electromagnetic spectrum. The light they emit is almost imperceptible to the human eye. Black lights appear to give off either no light at all, or only a dim, violet glow.

Fluorescent Materials

Materials are considered "fluorescent" if they have the ability to absorb ultraviolet light, then re-emit it immediately in more clearly visible, lower wavelengths.

Molecular Vibrations

Fluorescent materials dissipate the difference in energy between the absorbed and emitted photons of light through internal molecular vibrations.

Source:

Applications of Ultraviolet light

Definition of Fluorescence

More Information:

Chemistry Explained: Fluorescence