material, red safelights are used. Wratten No. 1,
1A, or 2 may be suitable. Some old photographic
plates were used without spectral sensitization,
called ‘‘color blind’’ plates. These materials are
sensitive to the blue and blue-green region; there-
fore, amber and red safelights can be used.
Most modern black-and-white pictorial films are
panchromatic, sensitive to all colors. Color materi-
als, whether negative or positive, film or paper, are
necessarily sensitive to all visible wavelengths to ren-
der natural colors. There is also a class of panchro-
matic black-and-white enlarging papers (e.g., Kodak
Panalure) used to produce black-and-white prints
from color negative films with natural tonal rendi-
tion across colors. All of these materials cannot be
safely illuminated by visible light for the duration of
darkroom handling, and they are often handled
under complete darkness; slow materials may be
briefly visualized under very dim green safelight
(Wratten No. 3 filter). Some fast materials may be
deliberately impaired of their light sensitivity by
treating in desensitizing dye solution before brief
visual inspection. The peak wavelength of 510 nm
(dark green color) is chosen for the safelight because
human eyes are most sensitive to this region, and
panchromatic materials are often least sensitive in
this region. To avoid the risk of fogging, dim green
safelight can be used for only a brief moment with
such materials. An alternative is to use infrared illu-
mination and a vision scope.
Some infrared films, particularly those for graphic
arts applications, are not very sensitive to green
light, and may be used with dim green safelight.
However, the safelight filter must eliminate infrared
radiation from the light source. The Wratten No. 7
filter is made for this purpose. (The dark green
Wratten No. 3 filter passes some red radiation and
this is unsuitable for infrared material.)
Development of films and plates under safelight is
called ‘‘development by inspection’’ and this was
customarily performed before panchromatic materi-
als became widely used. Orthochromatic plates were
insensitive to red light, making it possible to develop
them by visual inspection under red safelight. Pan-
chromatic plates and films must be handled in total
darkness, with brief use of dim green safelight at
most. Despite this limitation, panchromatic materi-
als became widely used when darkroom workers
started to precisely control negative contrasts by
development time and temperature. Introduction
of daylight processing tanks, accurate exposure
meters, and improved quality control in film pro-
duction also contributed to popularize panchro-
matic materials.
When selecting a suitable safelight, consult the
film or paper manufacturer’s recommendation for
the particular product, and choose type and num-
ber of safelights based on the darkroom size and
configuration. Multiple products can be usually
handled in one safelight as long as the light is safe
to the most sensitive material in terms of spectrum
and photographic speed. For typical black-and-
white printing with graded or variable contrast
enlarging papers, safelights with a Wratten OC
(dark amber) filter are safe up to a few minutes at
the recommended distance. With safelight exposure
longer than the safe limit, the image contrast may
become lower, or fog may develop in the area where
imagewise exposure was not given. When working
in a darkroom, it should be noted that eyes require a
long time to adapt to large differences in the illumi-
nation level. One often perceives the first several
minutes in darkroom safelight as too dim and
finds difficulty in working. It is necessary to wait
for up to 20 minutes before the eyes become fully
adapted for the safelight illumination. Safelights
based on discharge lamps may also require several
minutes of operation before the luminance and
spectrum are stabilized to avoid adverse effects.
RyujiSuzuki
Seealso:Darkroom; Developing Processes; Film;
Film: Infrared; Print ProcessesFurther Reading
DePalma, J. J. ‘‘Filters.’’ InHandbook of Photographic Sci-
ence and Engineering. 2nd ed., Charles Noel Proudfoot,
ed. Springfield, VA: Society for Imaging Science and
Technology, 1997.
Eastman Kodak Company. ‘‘How safe is your safelight?’’
Eastman Kodak Publication K–4, 2001.
Ilford Imaging UK Limited. ‘‘Safelight filters and dark-
room lamps.’’ Ilford Fact Sheet, 2002.SAFELIGHT