In the physical world, light is emitted in the first instance from light sources such as lamps or the sun. But once it reaches a surface, it typically bounces.
Indirect lighting is critical to the realistic appearance of interior spaces in particular.
Yet, in standard rendering tools, objects are only lit by direct light sources, and not by light reflecting off of other objects in the scene. Thus it is often necessary to fill a 3D scene with lights that are intended to simulate the complexity and subtlety of indirect illumination. 3D artists are familiar with the concepts of diffuse color and specularity. The diffuse color of an object s material definition is its color in the layman s sense of the word. Specularity, or specular reflection, is shininess or highlights.