Important Facts About Safelights
In photography, the term "safelight" describes darkroom illumination that does not cause a visible change to light-sensitive material when it is correctly handled and processed. The word "safe" is relative. Most sensitized materials will be affected if you expose them to safelight illumination for an extended period of time. Because photographic materials vary in speed and sensitivity to different colors of light, the recommended bulb wattages and colors of safelight filters also vary. Safelight illumination will fog color films and papers; color print and transparency materials; most panchromatic black-and-white films (films that are sensitive to blue, green, and red light); and high-speed infrared films. You must handle these materials in total darkness.
Ideally, safelight filters should transmit only light that is outside the color-sensitivity (wavelength) range of the photographic materials they're recommended for. Safelight filters recommended by Kodak provide maximum transmission of those colors that the paper or film emulsion has relatively low sensitivity to. However, the color sensitivity of most emulsions does not end abruptly at a particular wavelength in the spectrum--most emulsions are somewhat sensitive to colors outside the intended range. This means that most papers and films have some sensitivity even to the colors of light transmitted by the recommended safelight filters. Therefore, always minimize the exposure of photographic materials to safelight illumination.
A safelight has three basic parts:
KODAK Safelight Lamps contains descriptions of a number of KODAK Safelight Lamps and appropriate uses for the different types. The Safelight Recommendations table lists typical sensitized products and the safelight filters recommended for use with them. The table also shows the bulb-wattage recommendation for each application. See the paper or film package for safelight recommendations for specific materials. Be sure to follow the recommendations for both the wattage of the bulb and the minimum distance between the lamp and the photographic material.
The "safest" color safelight filter for a particular material is not always the recommended one. For example, a red safelight filter often has less effect on photographic papers than the amber filter listed in the table. However, most workers find that they can judge print density or perform other functions better under an amber light. (So, although it is a slight compromise in protecting the paper from fogging, an amber filter improves working conditions.)
The apparent color of a safelight filter is only a partial indication of its transmission characteristics. Colored bulbs or other improvised safelights may appear to be the right color, but they may actually emit light (or other forms of radiant energy) that will fog a photographic emulsion. KODAK Safelight Filters are made to precise light-transmission and absorption standards that relate to the spectral sensitivities of photographic materials.
Safelight filters gradually fade with use. This means that they transmit more and more light of the colors that they absorb when they are new. You should plan to periodically change safelight filters. For example, if you use safelight lamps for 8 to 12 hours a day, you may need to change the filters every three months.
Bulbs eventually blacken and produce less light. To keep the illumination level consistent, periodically change bulbs. Noting the replacement dates on a sticker on the safelight housing will help you keep track of bulb and filter changes. We recommend that you change bulbs before running safelight tests.
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