Phantast wrote: "The simplest, or you might say, the crudest, is just setting the ambience to a respectable value." This is, as you say, simple and crude. It's very inexpensive in render terms, but the results usually leave a lot to be desired. The areas illuminated by just the ambient aspect of the material have a completely dead look, with no real shadows or contrast. However, using ambient materials but with the overall ambient color set to black whilst using True Ambience will result in very real looking indirectly lit areas. Perfect black shadows where appropriate; a proper gradient from light to dark; and, of course, radiosity like diffuse light and colour bounce. And not forgetting relatively horrible render times. ;-)