# What are the side effects of biasing brightness in continuous spectrum raytracing?

I want to model rays with a continuous range of frequencies so that I can get raytraced images with colour separation on refraction. I can model a light source with a specified frequency distribution by using the distribution to affect the probability of a random ray lying in a given frequency range, or alternatively I can choose frequencies from a uniform random distribution and make the brightness of each ray proportional to the frequency distribution at its particular frequency. I see the first as more physically accurate, but I suspect the second will give images that look "finished" with fewer rays. Is this intuitive suspicion correct? Are there any features that will be lost from the image with the second approach? Is there a way to get some of the speed increase without compromising the image?