I dug one up in the deep recesses of our school darkroom. I believe it was in use when the photo teacher had to do the yearbook. Anyways, I believe it was meant for inspecting film during development. The thing is quite opaque. I cannot see through it. It reminds me of my 87C IR filters 
Anyway, how does one use it? What bulb would be best? I only have the filter, not whatever box it attaches to...
Safelight with light shining through it...

Anyway, how does one use it? What bulb would be best? I only have the filter, not whatever box it attaches to...
Safelight with light shining through it...