My lab has an older large Fotodyne tabletop UV transilluminator for visualizing gels. It has a UV blocking cover that hopefully reduces UV that passes through, but I've always been suspcious as to how effective it is. Obviously this part can be replaced with a new one, but short of guessing on the recommended 50 hr lifetime, how would one know the level of UV passsing through? I considered simply placing a gel on top, but that is far from quantitative. I am really just curious if there is an easy to make and/or obtain sensor that could be used to know when UV expose could be considered dangerous.