"All Through the Night" (1941) is a Humphrey Bogart film, where a gang of Runyonesque sharpies uncover a plot by Nazi saboteurs to mine New York harbor and blow up America's newest battleship, right under our noses. (Don't ask me how it got there.) It was made between "The Maltese Falcon" and "Casablanca", and cast Peter Lorre as a Nazi enforcer who goes around with his own scary face light.
The effect is so strong- something like that Twilight Zone episode, "The Purple Testament"- it illuminates his face when all around is normal light,
My guess is, the light's attached to his waist somehow, it sticks out about a foot or two, and has a little reflector, angled up, like a teeny photographer's light.
Ohh, kids, highly scary!
Uh-oh, now it's on this guy! Maybe the Nazis are just really into mood lighting.
Nazi-mood lighting.
So, the Nazi saboteurs have a big meeting, where Pepe scopes out the crowd in his inconspicuous way (the guy with all the light up in his face)-
Bogey pretends to be one of them, and catches wise to the plot (on account of, the whole meeting being in English)-
Which blows his cover with Pepe, and his light-
- and they both rush upstairs to tell Conrad Veidt.
Who has a crazy idea, even for a Nazi, of attacking the battleship with a speedboat filled with TNT. Pepe's reaction is predictable:
"You stupid eediot!"
I'm not sure whether to include the ending, but I will say that Evil meets its fate in an appropriately-illuminated way. They invented Technicolor, and chiaroscuro was wiped off the Silver Screen.
Bye-bye, and buy bonds.