It depends on what you wan't to use ray tracing for. If you want to calculate global illumination with path tracing (which is a form of ray tracing) then you n

It depends on what you wan't to use ray tracing for. If you want to calculate global illumination with path tracing (which is a form of ray tracing) then you need multiple samples per pixel to get a noiseless result. Most of the time at least 500-1000 samples.