I wanted to replicate Rembrandt’s portrait lighting (a shortened version of it). However, I ran into a strange problem. No matter what I do, my meta-human’s ear remains illuminated, even though the light shouldn’t fall on it in any way. This light also cannot be reflected because it is too intense. I’ve taken some screenshots for clarity. I’m not a lighting artist, so I can’t really understand how this is possible. As far as I can tell, the ear can’t be physically illuminated at this angle or with this intensity. Lighting artists, am I mistaken, or is the lighting really miscalculated? The lighting is done using lumen, and the light is in a movable position.
This is probably due to subsurface scattering. It simulates lights ability to pass through and scatter within materials. This is usually done via approximations like thickness vale or maps. The thicker the material, the less light comes through. Ears are thin, so lots of light on the opposite side of the mesh is allowed to pass through.
The issue is that when you look at the ears from the side, instead of the front, you should have the heads thickness to obstruct the light but the thickness approximation doesn’t know this.
There are tricks you could do in the material graph to mitigate this. Off the top of my head you could increase the thickness value of different parts of the head within the subsurf shader based on viewing angle. If you make the thickness of the ear high when viewed from the side, light wouldn’t be able to pass through it, but you can have it low when viewed from the front to get the fleshy appearance.
It sounds like the truth, but I haven’t been able to get rid of this effect using subsurf profile. The most I could do was make the entire shadow part of the face glow, but it still didn’t look like what we see on the ears. My subsurf color is set to orange, almost brown, but ears are very white. It seems like the the light is simply ignoring a part of the face. I tried changing the face shader to two sided, but it didn’t help.
If you want to be absolutely sure it’s not due to SSS you can temporarily change the mat to a default lit material.
But if it’s not due to the thickness, it could be due to some project setting incompatibility. Not all of UEs light and shadow features work with every shading model fully yet.
Also make sure that the light has shadow casting enabled. Looking closer, it doesn’t appear the nose is casting any shadow on the face.
If shadows are disabled then what you see is an expected behavior. Surfaces would be lit based on their facing direction regardless of if there was an obstacle or not.
For the record Lumen doesn’t handle direct cast shadows at all. This issue is with cast shadowing. So either Cascading shadow maps, Virtual Shadow Maps, Megalights or RT shadows (or possibly a material issue). All of which are independent tech from Lumen .
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I fiddled with the settings for a while and eventually found a solution. When I enabled megalights, the shadows started working as expected, and the image looked more accurate. I’m not sure why this happened, as I only have one lighting source on the stage. It’s possible that megalights has a feature that disables unnecessary elements and helps resolve these issues. In any case, thank you for your suggestion. I never would have thought that megalights would be useful on a stage with a single lighting source.
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