Back in the 90s, I worked with a photographer who shot 4x5 chromes and nothing else. He would have me load his film in a closet, where after about 60 seconds, I could literally see the outline of my hand. I'd say, "Brad, I can see my hand in there!" He'd say "Don't worry about it. It's not enough to fog the film." And it was never once a problem for the two years I assisted him. It always freaked me out, though.
If you've ever flashed paper, you know how much light it takes to get to the threshold. It's always way more than you'd think, which is good.