Actually light sources have always been the only thing 'traced'. We used to use them to trick ray tracing in the early days of RenderMan (put an image in the li

Actually light sources have always been the only thing 'traced'. We used to use them to trick ray tracing in the early days of RenderMan (put an image in the lightsource so you can 'reflect' it). It's surface to surface and other GI effects that where late to the party. Nevertheless we often faked that with massive light counts. For the opening shot of Armageddon with the astroid hitting earth I used 20,000 point lights to represent secondary debris reentering the atmosphere. In 1998 or when ever that was it still only took RenderMan a few minutes to render each frame.