Understanding Neutron Radiography Reading V-Kodak Part 2 of 3

Exposed films are more sensitive to fogging from the safelight illumination
than are unexposed films. Hence, it is especially important to guard the
exposed films against prolonged exposure to safelight illumination. Note that
the screen- type films are more sensitive to fogging by safelight illumination
than direct- exposure films. A simple method of checking the safelight of
illumination is to test it with the fastest film used in the laboratory, as follows:
An exposure is made of a stepped wedge. In the processing room, the holder
is unloaded and the film placed in the area where it is normally handled. Part
of the film is covered with opaque paper. The remainder is exposed to the
safelight illumination for the maximum time normally needed for handling. The
test film is then given standard processing. If no density shows on the
uncovered part that received the safelight exposure, as compared with the
covered part, the lighting may be assumed to be safe.
Charlie Chong/ Fion Zhang
Radiography in Modern Industry. Rochester, NY: Eastman Kodak Co. 1980