Larry Clinton At Frankfort, (Central) Indiana
I usually wet the material with naphtha, alcohol, etc. then view the surface. Any scratch marks will show up WAY better then.
When I follow the proper sanding routine I rarely have any scratches left. IE: Sanding using the correct grit and not jumping grit sizes and cleaning between grits. Actually I find it is quicker when I follow the proper routine.
I doubt I would use a light on the sander as I like to do the final inspection wet!