Ultraviolet Terminology

The following glossary offers a brief summary of terms and definitions used in the application of UV lights and products.

Download The "Light Measurement Handbook" Click.  

Ultraviolet Light Spectrum: Light with wavelength ranging from 100-400nm. Catergorised as UVA, UVB and UVC.   Click to view spectrum

Photochemistry: Chemical reaction driven by the absorption of visible or ultraviolet light

Coherent Light: All photons are in phase. Eg Laser

Incoherent Light: Photons are at randon phases. Eg incandescent light bulb

Radiant Energy: Total amount of energy emitted from a source over a given period of time

Joule: 1 Joule= 1 watt x second (Ws)

Inverse Square Law: Irradiance varies in inverse proportion to the square of the distance. E=I/d2

Irradiance W/m2: Total radiant power incident from all upward directions on a surface. Units W/m2

Fluence Rate W/m2: Total radiant power incident from all directions onto a small sphere.

Fluence (UV Dose) J/m2: Total radiant energy of all wavelengths passing all directions through a small sphere. J/m2. Approptriate term for UV disinfection because a microbe can receive UV power from any direction.

Quantum Yield: Measurement of the photon efficiency of a photchemical reaction.

Radiometer: A device that senses the the total irradiance incident on a sensor element. The photon flow is converted into an electrical current.

Actinometry: An actinometer is a photocehmical reaction for which the quantum yield is known. The measurement of the chemical yield after exposure allows the determination of photon flow.

Refractive Index (n): The ratio of the speed of light into a vacuum to that of a specific medium.

UV Disinfection:  Photochemical reaction of a microbe absorbing light of the wavelength range 200-300nm. The light is absorbed altering the DNA thereby disrupting the cell membrane.The cell either dies or the microbe is unable to replicate