Impenetrable by light: film stored in lightproof containers. (adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "lightproof" in a sentence
"Pinhole cameras (also called camera obscura) are simple devices, essentially a lightproof box with a single small hole."
"Here's a short article on how to make a simple "snoot" -- a lightproof tube that tightly directs the light from your camera flash."
"You go into a soundproof and lightproof chamber about the size of a shower stall and float in water that's so full of salts that it's almost thick and you float like a cork."