standpipe to hold water in the sink at the correct depth,
yet still allow water to flow out (fig. 10-1).
The function of a safelight is to transmit the
maximum amount of light that can be used safely
without damaging the sensitized materials being
processed. The color sensitivity of different sensitized
materials varies. Therefore, the color and intensity of
transmitted light must be varied accordingly. A
darkroom safelight is the combination of a rated light
source and a filter designated to protect a specific
The word safe. of course, is a relative term since no
sensitized photographic materials are ever completely
safe from the effects of safelight illumination. However,
a filtered light is accepted as safe when the sensitized
materials can be handled under the illumination with no
evidence of fogging for at least twice as long as the
normal processing time. No procedures must be
followed precisely when safelights are used:
Figure 10-1.Photographic processing sink
Use only the size of incandescent bulb specified;
for example, 7 1/2 watt, 15 watt, or 25 watt.
Handle sensitized material at the distance
recommended by the manufacturer. This is usually
between 3 and 6 feet.
To determine whether a safelight is safe, you should
follow these procedures:
1. In the dark, place a sheet of unexposed film,
emulsion-side up, on the working area where the film is
to be processed.
2. Place several coins on the emulsion and turn on
the safelight. Leave the safelight on for twice the length
of time the film will normally be processed.
3. Process the film normally and check to see
whether there is less density in the areas covered by the
coins. When there is less density, it indicates the film
was fogged by the safelight and the safelight is not safe.
A safelight that causes fogging may be corrected by
replacing the filter, by installing a lower rated bulb, or