Why does campfire lighting look creepy? Various photography lighting guides state that when light is positioned above a face it looks natural, but when positioned below a person it looks unnatural or even "creepy".



This is sometimes used deliberately in movies to evoke fear.



The universal principles of design say that this is because we evolved on planet earth with a single sun, which is always above us. 

But there are plenty of natural situations where light could come from under us. Such as being reflected off the ground, snow, or water, or just sitting around a warm campfire.



I'm just curious if there are any known psychological reasons why lighting under a face might look unnatural or "creepy"? Or could it be that it's such a staple of horror movies that we're primed to perceive it that way?
There are situations as you mentioned where light can be from below, but they are extremely rare in our evolutionary past. Fire is quite recent: remove that one. Reflections from water or snow would require very strong light from above, so those are essentially removed as well. I think the creepiness comes from the unfamiliarity. Also see the Uncanny Valley, which describes similar feelings in response to near-human representations https://en.wikipedia.org/wiki/Uncanny_valley

A good test would be with non-human animals. Do they find bottom-lit faces fear-inducing?