Personally, I think it is a bad idea. Window film is not designed to contain UVC, as there is almost none of it at the earth surface.

You are asking in a wrong place. Film manufacturer may know better.

Should it be safe to operate germicidal tubes in fluorescent fixtures that have milk glass diffusers? I have a couple of 4 foot fixtures that have milk glass diffusers that I am considering running G36T8 tubes or G40T10 tubes inside.

Most of the time probably OK. I won't risk though. If you want a nice low pressure mercury color tubular lamp, go to a friendly local neon maker and ask for a mercury filled tube in clear glass. Cute and guaranteed 100% UV safe. You can order even Ne + Hg fill for some awesome effects!


Also, shining strong UVC on plastic diffusers may turn them yellow/brown rather quickly, ruining a look of otherwise nice fixture.

I would say it depends on your goal.

I have a small germicidal lamp that I use for PCB exposures, and in that case it's in a small box with good light seals. The way I know it's running is based on when the starter stops and the blue light that goes through the tombstones.

But for a demonstration, depending on the diameter, you could get some glass blowing tubes and that would block out most of the UV, while still retaining the tube look. And optionally UV block film if you want to be really safe.

Are you sure using germicidal, and not UVA lamp for PCB exposure? Most resists AFAIK are tuned to UVA light, there is just very low level of 365 nm UVA in germicidal lamp output, and UVC radiation at 254nm is not optimal and even can trigger wrong reactions.