Are rim lights cheating? No.
Are they realistic lighting? Yes.
Rim lights are a matter of exposure. If an image is exposed for darks, there’ll be more info in the dark areas and less in the light. In the hulk image, I wanted a bright daytime look, so I crunched the light values.
In the Ultraman image (left)I exposed for the darks, and since the lighter dark values, there’s less of a gap between the information in the dark/light. If I bump up the exposure (right), you get “rim lighting” or the over exposed light side.
In this image, while it may seem confusing since its dark, I exposed for the lights. There’s more information on the lit surfaces than the ones in shadow. (Not a lot, but it’s there) if I put this next to the Hulk... see the difference of where more value information is placed?
I tend to crunch values with exposure since it mimics a camera, which has a more cinematic feel, and often (not always) that leads to some form of rim light.
TLDR
Rim lights are part of realistic lighting, it’s just a matter of exposure.
ALSO, There are lighting situations that don’t lend themselves to rim lighting. Pick your lighting scenario, and decide what works best to support your intent and story needs.
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