of these arrangements can be used with either hinged or sliding doors. If a lightlock opens
directly into the exposure room, the lightlock must be equipped with lead-lined doors.
Thus, it is simpler if it opens into the control booth, where protection is already provided.
The color of the walls in the lightlock is unimportant. Safelight may be used if desired.
Minimum dimensions for a lightlock are determined by door size, the smallest practical
door being about two and one half feet by seven feet. One door normally swings inward
with sufficient room to close it before opening the other.
c. Labyrinth. The labyrinth, or maze, is not provided with doors. It prevents the
entrance of white light yet provides air circulation. Since it requires at least twice as much
floor space as a lightlock, it is seldom used. The height of the entrance should be limited
to seven feet to admit the minimum amount of light. The walls and ceiling should be
painted with a flat paint and safelight illumination should be provided. A straight passage
into the processing room should be made possible by placing a lightproof door in the
Illumination of the processing room can be broken down into several individual
aspects: white light, safelight, wet film illumination, and wall finish. Each of these
elements must be taken into consideration in the design of a processing room.
a. White Light. White light is necessary for many operations such as mixing
chemicals, cleaning tanks, caring for intensifying screens, and general maintenance of the
darkroom. Fixtures for white light should be strategically located and of sufficient intensity
to provide general illumination.
b. Safelight Illumination. Since x-ray films are sensitive to white light, they must
be handled either in darkness or under safelight illumination of the proper quality. Films
exposed with intensifying screens are approximately eight times more sensitive to safelight
than unexposed film. Therefore, safelight illumination must be designed to give enough
visibility in the processing room for the specialist to accomplish his duties, yet be subdued
enough to avoid harming unprocessed film.
(1) Light source and filters. A safelight consists of a light source and a suitable
filter combined in a lamp housing and giving light of an intensity and spectral quality which
will not fog film exposed to it for a reasonably short time. A combination that is
recommended and widely used is a 15-watt tungsten bulb with a Wratten 68 filter or Kodak
GBX. Light from such safelight is in the yellow or yellow-red portion, not in the same
spectral range as the film sensitivity. The wattage is sufficient to provide illumination
without undue fogging of the film.
(2) Arrangement. There should be one or more appropriate indirect type
safelights in the ceiling for general illumination with others strategically placed over work
areas. For specific areas of the room, there are safelights of various design, the choice of