S

SAFELIGHT

Safelights allow darkroom workers to handle
photosensitive materials under limited illumina-
tion. A safelight consists of a light source, such as
combusting gas or other fuel, incandescent light-
bulbs, fluorescent light tubes or sodium vapor dis-
charge lamps, and a filter to limit the range of
wavelengths that are used for illumination. Various
manufacturers have their own designations for
spectral transmission characteristics of safelight fil-
ters. A Kodak Wratten filter number is often used to
indicate the type of the safelight filter. In order to use
maximum illumination while securing safe handling,
the safelight should be suitably chosen for the type of
photosensitive material.
Photographic materials such as plates, films, and
papers are sensitive to light of certain wavelength
ranges but insensitive to other wavelengths. Dark-
room operations may be safely performed under
illumination of some visible wavelengths to which
particular photographic material is relatively insen-
sitive. For example, conventional black-and-white
enlarging papers are sensitive to ultraviolet and
blue light, and they are far less sensitive to yellow
and red light. Therefore, we customarily handle
these materials under red or orange safelights in
the darkroom. On the other hand, panchromatic
plates and films are sensitized to all visible colors,

and therefore cannot be safely illuminated by visi-

ble light. When necessary, dim green safelight may

be used, but only briefly. Thus there are consider-

able differences between materials and suitable

safelights depending on the factors such as spectral

sensitivity and photographic speed of the material.

Some silver chloride contact printing papers are

only sensitive to the ultraviolet and deep blue

region, and the sensitivity is also very low. These

papers were sometimes called ‘‘gaslight papers’’

since the materials could be handled in a room lit

by gaslight. Many classical processes predating sil-

ver gelatin process were also slow and insensitive to

most, if not all, visible light, and they could be

handled under dim room light without special fil-

tration. Graded enlarging papers are also sensitive

to ultraviolet and blue light only, so greenish-yel-

low safelight filters such as a Wratten OA filter can

be used. Some fast enlarging papers and variable

contrast papers are sensitive to blue and green, so

amber safelight is used, with a Wratten OC or

similar filter. Sodium vapor discharge lamps with

amber filters are used for products of these cate-

gories in large darkrooms.

Orthochromatic materials are made sensitive to

blue and green colors. Depending on the wave-

length of sensitivity limit and the speed of the