Emission Material
The back wall covered with an Emission Material illuminates the rest of the scenery.
Note:
This Node is only available when editing a classic Cinema 4D Node material.
The Emission Material behaves similarly to a usual Standard Material with only activated Luminance channel (polygon lights, for example, thus carry such a material). It therefore emits light without having to be illuminated itself. For example, use this material if you want to place an HDRI material on a sky object or otherwise make objects glow.