Nvidia G80 GPUs and the Geforce 8800 GTX or Ultra can support an advance way or
calculating the light in the scene called Ray casting. This is an alternative
way or showing the light a bit less advanced as the ultimate goal and the best
lightning method called Ray tracing.
Ray casting will give you a more realistic light than any other model used in the real time graphics and games today but it will extremely "expensive" as it needs a lot of GPU power.
Ray casting is still limited as you don’t calculate all the bounces of the light and the ray intersections, you can limit the numbers of bounces and intersections to make the calculations easier.
Nvidia is working on a cool demo and this will come soon enough and I can guarantee you that the light will look better then ever before, and all that in real time. R600 should be able to cope with this as well.