When you say "black electrical tape" do you mean from, say, Harbor Freight, or from 3M? Since the 3M stuff blocks UV fairly well, i can't really see light getting through it, although i'd have to find some to test.

years and years ago we'd buy a roll of film, pull it out in the sun, and then get it developed but not printed. You could use that as an IR-passthrough filter on a camera lens - this is if my memory isn't faulty.