Ultraviolet photography

Ultraviolet photography is a photographic process of recording images by using light from the ultraviolet (UV) spectrum only.

Light which is visible to the human eye covers the spectral region from about 400 to 750 nanometers. This is the radiation spectrum used in normal photography. The band of radiation that extends from about 1 nm to 400 nm is known as ultraviolet radiation. UV spectrographers divide this range into three bands:

Only near UV is of interest for UV photography, for several reasons. Ordinary air is opaque to wavelengths below about 200 nm, and lens glass is opaque below about 180 nm. UV photographers subdivide the near UV into:

(These terms should not be confused with the parts of the radio spectrum with similar names.)

There are two ways to use UV radiation to take photographs - reflected ultraviolet and ultraviolet induced fluorescence photography. Reflected ultraviolet photography finds practical use in medicine, dermatology, botany, criminology and theatrical applications.

Sunlight is the most available free UV radiation source for use in reflected UV photography, but the quality and quantity of the radiation depends on atmospheric conditions. A bright and dry day is much richer in UV radiation and is preferable to a cloudy or rainy day.

Another suitable source is electronic flash which can be used efficiently in combination with an aluminium reflector. Some flash units have a special UV absorbing glass over the flash tube, which must be removed before the exposure. It also helps to partly (90%) remove the gold coating of some flash tubes which otherwise suppresses UV.

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