Measuring Your Exposure Unit's Output

While it may be common to periodically measure your exposure units light output, keep in mind that it is also necessary to measure the output with and without the vacuum coversheet over the light meters aperture.

To insure optimization in the photopolymer platemaking process we measure the light output of the exposure lamps using a UV-A meter for main and post exposure lamps, and a UV-C meter for Detac or germicidal lamps. A reading is taken in each corner of the exposures bed, or platen, in addition to one measurement from the center of the bed. By gathering this data periodically, we can see the drop off in the lamps functionality. As the lamps continue to diminish, exposure times must then lengthen in time to make up for the diminishing return. However at some point (see manufacturers recommendations) the lamps output will diminish to the point that it no longer makes sense to continue extending exposure times due to the excessive wear on equipment and detrimental effect on productivity.

Along with taking these light readings it is also necessary to take the same 5 readings with the vacuum coversheet drawn. If the output decreases by at least 20% with the coversheet, you must replace the vacuum coversheet material. The coversheet will naturally gain in opacity due to a waxy build up resulting from waxes in the raw sheet photopolymer material. The result is less light passing through the coversheet, thus once again necessitating longer exposure times, or a loss in productivity. Typically, the life expectancy for UV-A lamps is 400-600 hours and 800-1200 hours for UV-C lamps. Most newer plate exposure units have hour timers on them that can be used to keep track of the number of hours your lamps have been in use. Record this information in a spreadsheet each time your lamps are replaced. If you do not have access to UV meters, you are left with a couple of alternatives for tracking your exposures. First, use your hour timers and establish a set number that you will change the lamps i.e. 400 hours. Your other and best alternative is by checking the quality of your plates, you will most likely see the effects of weak exposure lamps in the dot areas of your plate first, i.e. you are no longer holding the 3% dot where you previously held it.

For more information on this issue, please contact: info@teamflexo.com

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