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Glossary of Terms


An index of light or UV absorbed by a medium compared to the light transmitted through it.

Actinic Light

That light which causes change in the nature of a photosensitive medium.

Additive lamps

Medium pressure mercury vapor UV lamps to which metal halide(s) have been added to alter the output wavelengths. Previously called doped lamps.


A characteristic of a surface that reflects or scatters light or UV equally in all directions.

Doped lamps

See additive lamps.

Emission Spectra

Radiation from an atom or atoms in an excited state, usually displayed as radiant power vs. wavelength. Extends from radio waves through visible and UV to gamma rays.

Energy Density

Radiant energy arriving at a surface per unit area, usually expressed in joules or mill joules per square centimeter. It is the time-integral of irradiance. Same as exposure. For a parallel and perpendicularly incident beam, not scattered or reflected, energy density and fluency become identical.

Flux (radiant flux)

The flow of photos, in einstein/second = one mole of photons.


Unit of length. Abbreviated nm. Equals 10-9 meter, 10-3 micron, 10 Angstrom. Commonly used to define wavelength of light, particularly in the UV and visible ranges of the electromagnetic spectrum.



Spectral Output

The radiant output of a lamp versus wavelength. It is displayed in a variety of ways, but most commonly as a graph or chart of output watts plotted against wavelength. The appearance of the plot will vary dramatically, depending on the wavelength resolution used. A technique of normalizing is to integrate spectral power over 10 nanometer bands, to reduce the difficulty of quantifying the effects of line emission spectra.


Ultraviolet light energy. Radiant energy in the 100 – 400 nm range.


Volatile Organic Compound


A fundamental descriptor of electromagnetic energy, including light. It is the distance between corresponding points of a propagated wave. It is the velocity of light divided by equivalent frequency of oscillation associated with a photon. UV wavelengths are typically measured in nanometers (nm).

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