Is Your Lighting Safe?

Are the lighting conditions in your shop safe to move an unexposed stencil into?

Surprisingly, many screenprinters believe that you must never place an unexposed stencil in ordinary room light. Others still believe that you have to use red safe lights or work in complete darkness. You may be surprised to learn that not only can you coat your mesh in ordinary room light, you may be able to leave that unexposed stencil in ordinary room light much longer than you thought. Here is an easy test to solve the riddle.

Begin by placing eight coins on a dry, but unexposed screen. Place the screen in ordinary room light, but away from any direct sunlight that may enter your shop. Set a timer (portable or on your phone) for 1 hour. When the alarm goes off remove the first coin. Reset the timer for another hour and repeat the process of removing another coin.

At the end of the day, develop the stencil as you normally would and you will have a visual indicator of how many hours the screen could have been left in the shop without being exposed. The area that was covered a coin, effectively blocked the light from hardening the emulsion.

The uncovered stencil will have received a total of 8 hours exposure to the ambient light. The area under the eighth coin received one hour of exposure. The area under the seventh coin received two hours of exposure, etc.

If any area washed out that was behind a coin, it indicates that the light did not affect the stencil in the time associated with that coin. Thus, if the area under the last five coins did not develop then it is safe to assume that the ambient light did not effect the stencil with five hours of exposure.

If you prefer, you can write the number of hours under the associated coin as a reference.

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About Bill Hood 413 Articles
Bill Hood is an International Consultant in the Screenprinting Technologies, focusing on consistency, predictable outcomes and reproducible results. He is the author of over 50 books on the screenprinting technologies as well as thousands of technical articles, many of which are available at online. He writes for Solutions Journal Magazine and other trade publications, is a speaker at various events and has judged international screenprinting competitions. He can be contacted through his website at online.