Notice in the left image above, the bottom sphere has a burnout region close to where it contacts the top sphere. This is caused by the fact that the emitted radiance of the top sphere is 3.0. Therefore, points in the top part of the bottom sphere get more light than they could handle. I thought that this was a good time to implement Tone Mapping. As you can see in the right image, I have mapped the maximum luminance of the scene to 1.0. No more burnout can be seen.

Below is another set of images, displaying the same scene, with the emitted radiance of the top sphere being 6.0. The maximum luminance of the scene is still the same as above. The result: a little bit of burnout left to be seen.

Touching spheres

Touching spheres with tone mapping