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Ultraviolet induced fluorescence:
Since the radiation emitted as a result of ultraviolet stimulation is always in the visible region of the spectrum, films with conventional spectral sensitivity, either black-and-white or colour, are suitable. Colour is, however, most often used to record the characteristic colours of many types of fluorescence. Fast film is essential - the luminous intensity of most fluorescence is very low indeed. The choice of black-and -white versus colour will depend on whether it is important to record the colour of the fluorescence or simply to capture a record of its presence. If the latter is the case, Kodak T-Max 400 either rated normally, or if the fluorescence is very weak "push" processed up to 3200 ISO, is excellent. For colour work the authors recommend Kodak Ektachrome P800/1600 "pushed" if necessary to 3200 ISO. ("Push processing" is the term used to indicate a longer than normal time in the developer, or in the case of colour reversal film the first developer, which results in a higher than normal effective ISO film speed.) The enhanced contrast obtained by push processing the films also adds to the clarity of the fluorescent record. Both the T-Max and the Ektachrome P800 films have a built-in ultraviolet absorption filter in the overcoat of the emulsion that helps eliminate any of the reflected ultraviolet radiation.