Bill Tindall, E.Tn.
I like hand sanding because it gets me intimate with the task and goal. I can detect sanding deficiencies under any lighting conditions used for sanding-indoor, outdoor. I can readily detect anything that will cause a pigment stain to reveal even more of the defect. It seems to me that these defects are so obvious that anyone could see them under any reasonable light- unless they are covered up by sanding dust? Bottom line- I think the problem is knowing what to look for and how, not the light. Hand sanding and pigment staining is good training.