How Safe Is Your Safelight?


Testing Your Safelight Conditions

Test for Black-and-White Papers

Before starting the test--

  • Install a new bulb in each safelight housing, and verify that you've selected the correct wattage for the paper you are using.

  • Inspect your darkroom for light leaks. Turn off the white lights. If the room light is provided by fluorescent tubes, wait at least 5 minutes for the residual glow to dissipate. Then check to be sure that no white light is entering the darkroom through doorways, passthroughs, etc. (Remember, it takes at least 10 minutes for your eyes to become fully adjusted to the dark.)

  • Correct any light leaks. Make sure that no white light is escaping from the enlarger or safelight housings.

After you have prepared the darkroom, test your safelight conditions by following the steps below:

  1. Set up the enlarger. Insert the negative carrier with no negative in it into the enlarger. Set up the easel with a mask to expose an area as shown in Figure 1, below.

  2. Turn the white lights off and turn the safelights on. Determine which paper-handling area receives the brightest illumination. This will usually be the area where you process prints.

  3. Turn the safelights off, and run a test to determine what enlarger exposure is required to produce a light gray tone on the photographic paper with standard processing. You will probably have to set the lens to its smallest aperture and use a very short exposure time. Place a sheet of the photographic paper under the mask on the easel, and expose it. Process it in total darkness. Compare the unexposed area to the exposed area. The gray tone should have a reflection density of 0.25 to 0.50 (0.15 to 0.40 above the paper density) as measured with a reflection densitometer. Or you can make a visual comparison of the exposed area with the gray-scale steps in KODAK Publication No. Q-16, KODAK 24-Step Reflection Density Guide.

  4. Make the first enlarger exposure. All the lights should be off. For orientation, cut a corner from a fresh sheet of the photographic paper, and position the paper under the mask (see Figure 1). Expose the paper, using the time and aperture you determined in step 3. Label this area "After" to indicate safelight exposure that occurs after the enlarger exposure.

  5. Make the safelight exposures. With all the lights still off, place a large piece of cardboard on top of the developer tray or in the area where safelight illumination is brightest. Place the photographic paper on the cardboard. Using an opaque card, cover about one fourth of the paper. Turn on the safelight, and expose the uncovered part of the paper for 1 minute. Move the card to cover half of the paper, and expose the other half for an additional 2 minutes. Cover all but one fourth and expose it for 4 more minutes. The four parts of the paper will have received 0, 1, 3, and 7 minutes of safelight exposure. (See Figure 2.)

  6. Make the second enlarger exposure. With the paper oriented as in step 4 (Figure 1), position the marks to expose the opposite side of the paper. Give this area an exposure identical to the one given in step 4. Label this area "Before" to indicate safelight exposure that occurs before the enlarger exposure. (See Figure 3.)

  7. Process the paper in total darkness.

  8. Evaluate the test. The illustrations labeled "Test A," "Test B," and "Test C" in Evaluation of Safelight Test for Black-and-White Papers show three possible results.

Safelight Test Procedure for Black-and-White Papers


Test A in Evaluation of Safelight Test for Black-and-White Papers shows no added density on either side of the paper as a result of safelight exposure. This condition represents a safe time of at least 7 minutes.

Test B in Evaluation of Safelight Test for Black-and-White Papers shows a potentially unsafe condition. The part of the paper that received a 7 minute exposure to the safelight alone is fogged. (Compare the density shown in the bottom fourth of the paper to the center and the borders of the rest of the paper.) The paper also shows signs of image change starting at 1 minute in the "Before" area, and at 3 minutes in the "After" area. This means that you must handle the paper very carefully before and after the enlarger exposure. If your safelight filter is old, results like these could indicate filter fading; replacing the filter should give you a longer safe time. If the filter is new, you can extend the safe time by using a lower-wattage bulb; moving the safelight lamp to a greater distance; using only dim, indirect safelighting for handling; or developing the paper for half the total time with the safelight off. Of course, you could avoid the risk of fogging if you develop the paper without any safelight illumination, or adhere strictly to the safe time indicated by the test.

A more typical result is shown in Test C in Evaluation of Safelight Test for Black-and-White Papers. The paper is safe for up to 7 minutes of safelight exposure before the enlarger exposure, and up to 3 minutes of safelight exposure after the enlarger exposure. The test indicates that conditions are safe if you limit the total safelight exposure time to 3 minutes.

Some products are more sensitive to one sequence of exposures than to another. You can compare products by using this test or variations of it.

Tests for Other Photographic Materials

Blue-sensitive and orthochromatic sheet films are sometimes loaded into holders and processed in trays under safelights. You can devise a test for determining a safe time for these materials that is similar to the "Test for Black-and-White Papers." However, instead of exposing the film with an enlarger to provide the gray-tone exposure, expose the film in a camera.

Make a test object by mounting a KODAK Gray Card (KODAK Publication No. R-27) vertically on a jet-black, non-reflective background. Take a meter reading of the test object (including the black borders around the gray card). Then set the camera aperture and shutter speed to give about 1 stop less exposure than the meter indicates. You are now ready to expose two separate sheets of film.

Load two sheets of film into a film holder in total darkness. Make a camera exposure of the test object with the first sheet of film. Label this film "After" because safelight exposure will occur after camera exposure. Next, expose sections of the sheet of film to the safelight where you process the film. This is similar to the test for paper, except that you should try a total of 0, 4, 7, and 13 minutes, respectively. One quarter of the sheet receives no exposure. The next quarter receives 4 minutes. A third quarter receives 7 minutes (4 minutes + 3 minutes). The last quarter receives 13 minutes (4 minutes + 3 minutes + 6 minutes).

Then take the second sheet of film and expose sections of it to the safelight where you load film into holders. Use the same safelight exposure times that you used for the first sheet. Then make a camera exposure of the test object, using the same aperture and shutter speed as for the first sheet of film. Label it "Before."

Process both sheets of film in total darkness. After normal processing, a continuous-tone film should have a transmission density of approximately 0.4 in the gray-card area. The black border surrounding the gray card should not differ appreciably in density form the gross fog level of the film.* If the density of the gray-card area exceeds 0.4, or the density of the black border is much greater than the gross fog level, safelight fog may have occurred. You can evaluate your results by comparing them to the conditions described in step 8 under "Test for Black-and-White Papers."
*The transmission density of a completely unexposed and normally processed sample of the film.


Evaluation of Safelight Tests for Black-and White Papers


You can also adapt this test for use with papers in rolls. Roll papers that are printed in automatic or semiautomatic printers are susceptible to safelight exposure when you load and unload the printer, and when you load the paper into a processor. Adapt the safelight test to these operations by carefully studying your paper-handling procedures.

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