How Safe Is Your Safelight? a GUIDE to DARKROOM ILLUMINATION
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Publication K-4 •October, 2006 How Safe Is Your Safelight? A GUIDE TO DARKROOM ILLUMINATION IMPORTANT FACTS ABOUT SAFELIGHTS “KODAK Safelight Lamps” contains descriptions of a number of KODAK Safelight Lamps and appropriate uses for the different > No safelight provides completely safe exposure for types. The Safelight Recommendations table lists typical sensitized an indefinite period of time. products and the safelight filters recommended for use with them. > Safelight filters are designed for specific types of The table also shows the bulb-wattage recommendation for each paper and film. application. See the paper or film package for safelight > Safelight filters fade with use. recommendations for specific materials. Be sure to follow the > Poor safelight conditions can produce a loss in recommendations for both the wattage of the bulb and the photographic quality before actual fogging is visible. minimum distance between the lamp and the photographic > Many photographic materials require handling in material. TOTAL darkness. 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 Therefore, you should • listed in the table. However, most workers find that they can judge Follow all safelight recommendations for your paper or film. print density or perform other functions better under an amber light. See product instructions for recommended safelight filter, (So, although it is a slight compromise in protecting the paper from bulb wattage, and minimum safelight distance. fogging, an amber filter improves working conditions.) • Test your safelight conditions regularly. The apparent color of a safelight filter is only a partial indication • Replace your safelight filters when necessary. of its transmission characteristics. Colored bulbs or other improvised safelights may appear to be the right color, but they may In photography, the term “safelight” describes darkroom actually emit light (or other forms of radiant energy) that will fog a illumination that does not cause a visible change to light- photographic emulsion. KODAK Safelight Filters are made to sensitive material when it is correctly handled and processed. precise light-transmission and absorption standards that relate to The word “safe” is relative. Most sensitized materials will be the spectral sensitivities of photographic materials. affected if you expose them to safelight illumination for an Safelight filters gradually fade with use. This means that they extended period of time. Because photographic materials vary in transmit more and more light of the colors that they absorb when speed and sensitivity to different colors of light, the they are new. You should plan to periodically change safelight recommended bulb wattages and colors of safelight filters also filters. For example, if you use safelight lamps for 8 to 12 hours a vary. Safelight illumination will fog color films and papers; color day, you may need to change the filters every three months. print and transparency materials; most panchromatic black- Bulbs eventually blacken and produce less light. To keep the and-white films (films that are sensitive to blue, green, and red illumination level consistent, periodically change bulbs. Noting the light); and high-speed infrared films. You must handle these replacement dates on a sticker on the safelight housing will help you materials in total darkness. keep track of bulb and filter changes. We recommend that you Ideally, safelight filters should transmit only light that is change bulbs before running safelight tests. outside the color-sensitivity (wavelength) range of the photographic materials they’re recommended for. Safelight TOTAL-DARKNESS MATERIALS filters recommended by Kodak provide maximum transmission of those colors that the paper or film emulsion has relatively low Because of their sensitivity to light of all colors, you must handle the sensitivity to. However, the color sensitivity of most emulsions following types of films, plates, papers, and materials in total does not end abruptly at a particular wavelength in the darkness: spectrum—most emulsions are somewhat sensitive to colors • Panchromatic black-and-white films and plates outside the intended range. This means that most papers and • Color camera films films have some sensitivity even to the colors of light • Slide and print films (for making transparencies from color transmitted by the recommended safelight filters. Therefore, negatives) always minimize the exposure of photographic materials to • Duplicating and internegative films safelight illumination. • High-speed infrared films A safelight has three basic parts: • Color reversal papers 1. The lamp housing. This holds the bulb and the filter, and • Color negative papers and materials designed for Process RA-4 keeps the white light emitted by the bulb from escaping. 2. The safelight filter. This absorbs light of some colors and SAFELIGHT RECOMMENDATIONS transmits light of others to varying degrees. 3. The bulb. The recommended wattage is determined by the KODAK Safelight Filters are available in sizes to fit KODAK Safelight sensitivity of a particular material, the transmission Lamps. Their transmission characteristics make them suitable for characteristics of the filter, the type of illumination the use with a number of photographic materials (see the Safelight lamp housing provides—spot (direct) vs. general Recommendations table). (indirect)—and the distance between the safelight and the area where you handle the material. Blue-Sensitive and Orthochromatic Black-and-White Films. You can handle these types of films under red safelights. The spectral sensitivity and the speed of the particular film determine the safelight filter that you need. See the Safelight Recommendations table. ©Eastman Kodak Company, 2006. Black-and-White Papers. Black-and-White papers are Safelight Recommendations developed in processors or by inspection trays. Safelight Frosted Bulb illumination is generally brighter near the trays than it is Direct anywhere else in the darkroom. Be sure that this illumination is Illumination safe for the total development time. Excessive exposure to KODAK (No closer proper safelight illumination, or normal exposure to unsafe Safelight For Use with These than 4 ft Indirect illumination, will degrade the highlights and lower print contrast. Filter Color Materials [1.2 m]) Illumination Light Contact and enlarging This occurs before actual fogging is visible in areas that receive OC* 15-watt 25-watt amber papers. no white-light exposure, such as print borders. As a result, a Some blue-sensitive questionable safelight condition might not be detected for some materials, most 1 Red 15-watt 25-watt time. (See the “Test for Black-and-White Papers.”) phototypesetting Safelight exposure can occur before and after the printing materials. exposure. A low-level overall exposure either before or after the Slow orthochromatic Light 1A materials. High- 15-watt 25-watt printing exposure is technically referred to as a “super-additive red exposure.” “Safe time” for safelight exposure is defined as any resolution plates. Fast orthochromatic exposure time less than or equal to one-half the time required Dark 2 materials. Some green- 15-watt 25-watt for a safelight to produce a detectable change in a particular red sensitive x-ray films. sensitized product. Virtually all exposures are cumulative and Dark Some panchromatic Not 3 15-watt can cause contrast and density changes. The tests "Test for green materials applicable Black-and-White Papers" and "Tests for Other Photographic Not 7B Green Infrared laser films. 7 1/2-watt Materials" will help you determine a safe time for your Applicable application. Color negative papers Panchromatic papers are more sensitive to the safelight Dark and materials, 10 15-watt 25-watt illumination normally used with black-and-white papers. To help amber panchromatic black- protect these papers against image-quality change and safelight and-white papers. fog, use them with special filters or small-wattage bulbs (see Color negative papers, the Safelight Recommendations table). Safelight specifications 13 Amber panchromatic black- 7 1/2-watt 15-watt and-white papers. are printed on the package. Recommendations for safelight Most blue- and most filters for specific Kodak photographic materials are based on GBX-2 Red green-sensitive 15-watt 25-watt test procedures similar to those described in ANSI Standard medical x-ray films. PH2.22-1998. *The OC filter has been formulated so it can be used with photographic materials in place of an OA filter. Color Materials. Handle color camera films, duplicating films, internegative films, slide and print films (for making PLACEMENT OF SAFELIGHT LAMPS transparencies from color negatives in total darkness. Also handle papers and materials for Process RA-4 in total In black-and-white printing rooms and other areas where general darkness. safelighting is acceptable, position ceiling safelights so that the However, if absolutely necessary, you can use a safelight illumination is evenly distributed over the entire area. You can then equipped with a KODAK 13 Safelight Filter (amber) and a 7 1/2- place individual lamps where you need them most—at the watt bulb. Keep the safelight at least 4 feet (1.2 metres) from processing sink, for instance. Do not place direct illumination closer the paper. Run test to determine that safelight use gives