A light leak is any light - other than that focused through the lens - that gets inside the camera body. Light leaks can spoil film while it is in the camera.
Light leaks generally show up as bright streaks or fogging on film, and are often due one or more of the following:
- the deteriation of foam seals around a film door on older cameras.
- cracks or pin holes in the bellows of folding cameras
- poor manufacturing standards, as in the case of the Holga.