I know we are all familiar with the small testing devices for our curing lights. In truth though I never used one, more because I didn't know how to interpret the data then anything else.  The exact number when we test is really not that important. What we watch for is a trend. If the number starts to diminish over time it is an indication that our light or light guide may need maintenance. Making sure we are adequately polymerizing is critical, and this is one way to assure that.