This is the first result worth looking at:
The main thing to notice here are the soft shadows. A small change, but 'realism' awaits. There are some incorrect results in this image, because you can see the diffuse reflection of the green box is still biased. The local shading model from two lights draws the reflecting rays in their direction, meaning this is not a totally correct result.
The box in the middle suddenly became radioactive and now emits light. The image is still biased, even the emitting box only emits towards the light sources.
Experimenting with rougher surfaces and more glossy surfaces.
The first results of refracting rays.
Perfectly refracting sphere showing the bias is indeed gone here. The grain is also gone since I actually took the time to sit back and wait for the image to converge (this image took about two minutes to converge to this state).
The same scene with different materials and a more emitting 'roof'.