Abstract: The ambient term in a renderer is a constant color added to all points yielding a crude global approximation to indirect lighting. Because the ambient term ignores geometric occlusion conditions, it is computationally inexpensive. We present an extended ambient term that provides better reults than the constant term, but is still inexpensive, because it also does not compute occlusion conditions. It is based on the idea of finding a six-sided axis-aligned environment which is similar in color and area to the real scene, and deriving an approximation to indirect lighting by computing interreflections in the simplified scene.