I'm building a VR art gallery concept with black walls and ceilings. I don't want to have a visible light source, so I made the ceiling emissive. However, this only seems to work if I keep it white. Aside from the emissiveness of the ceiling, I want the material settings of the ceiling to match that of the walls, which are composite rubber from the Material Library VX. Is this possible?
To make a black surface emissive, you have to "trick" blender by mixing a visual black surface, with a light producing, white emission (emission must have some "whiteness" to be considered a light source), using the Is Camera Ray output of a Light Path node as a Mix Factor (to give the look of one, but the light from the other). Use this for your ceiling material:
This also works with full PBR texture sets if you want - just add your setup in place of the Diffuse Shader in my first image. In the example below, I am using an "asbestos tile" PBR set as the material while still giving light, so you can use your rubber material here. But keep in mind that since your material is also "the same" as the light source, it does not light itself very well - only through bounced lighting, so it may be very dark itself.