Please first see this image:
I would like to understand what is causing the jagged black shaded edge you see on the left side of the sphere.
My program has variance in hundreds of parameters but I only see this effect occasionally - perhaps one in 30 scenes. Most often when the sphere is blue.
The sphere is a textured, lit gluSphere. Increasing slices/stacks doesn't help. There are always one or more light sources in the scene. The sphere has a little specular and shinyness. However, after playing around with the various material and lighting params I can't deduce the real cause, or a rule to avoid the problem.
Would appreciate any assistance!