Hey guys,
Is there a way to make the inside of the mouth and nostrils dark in eevee?
Thank you.
Great question, @Claudius! Although the answer is probably highly dependent on your scene, I will share an old trick that isn’t physically accurate, but it may give you artistic control that you didn’t know you had.
In Blender, lights are given power values that equate to their energy in the render engine. This is a numerical slider/number input that looks like this:
You’ll notice in my scene that I have two lights. The other one is set at the default 1000w, as well. You might think that the lowest you could set a light value is 0, but you’d be wrong. Blender allows you to set light power to a negative value! You have to type it in as the slider stops working at 0, but it does allow it. And then, guess what…Blender starts to subtract light from your scene! See:
Again, this is not going to add to realism, but you can use it inside your character’s mouth/head mesh to reduce light in a way that looks better artistically. Just tweak the power and radius until you get the look you are going for.
I would like to know more about your scene (a screenshot would be great) so I can help think of other ways to help you get the look you want. Happy Blending!
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@Claudius
Make sure each light has “Shadows” and “Contact Shadows” enabled.
Contact Shodows OFF
Contact Shadows ON
Simple and Easy 
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@Hunkadoodle’s answer is very good. You can also simply use texturing to darken areas that you want to be dark. This is common practice in CG; the lights and shadows do not have to be the only thing deciding what’s bright and what isn’t.
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In my experience, regular lights (with sufficient bit depth/resolution/clip) get shadowed just fine on the inside of the mouth. But if you’re using HDRI lighting, you’re likely to have some problems, because it doesn’t get occluded.
This is exactly what AO is made for. If you’re not using a 1m = 1 unit scale, you probably need to adjust the distance used in properties/render/AO.
A better but slower solution is, avoid world lighting and use more actual lamps.
Thank you Hunkadoodle and all of you guys for the advice. They’re very good ones.
And about your trick I’d never have figured it out. Who would’ve imagined that light power could be set to a negative value. Very interesting indeed.
So, i haven’t figured out yet how I wanna create my scene. My goal is to build the most photorealistic scene possible to be seen in VR.
Cause when it comes to photorealistic CGI I’m an enthusiast. Both in movies and also videogames.
So my idea is to create a sort of showcase in order to give people a sense of awe in VR. Not a game but with some elements of interaction.
Cause VR games are cool, but IMO they still can’t deliver a sense of being in another place cause, for performance reasons, everything looks so unrealistic.
But anyway, it’s just for fun. The world of CG is really fascinating isn’t it? Especially when it strives for simulating the real world despite all its complexities.