The first mention of this I have seen is in Aristotles *Generation & Corruption*; he suggests that according to Democritus, even if the space between a lamp and a wall was completely *void*, light will be still cast onto the wall.

Aristotle disagrees with this, and states if the space between the lamp and the wall was properly void nothing, including light, would reach the wall; he's implicitly saying that Democritus notion is actually a vacuum and not a void - he goe's into more detail of this in his *Physics*.

It's this notion thats later codified into the principle of *locality*, of which there are a few variants.