Here is information on how I optimized the lighting on my cabbing and polishing unit including the overhead light.
I use a 100 watt clear light bulb in a "gooseneck" fixture for my jewelry work bench, my cabbing machine and my polishing unit. The clear light provides a point source spot similar to the sun. It enhances the surface of the cab and allows you to see imperfections, scratches and mini flat spots better than the frosted bulbs. I also enhance my vision with cheap (Dollar Store) reading glasses with 3.5 diopter power. I prefer these to an optivisor because they are more comfortable and you dont have the top frame of the Optivisor blocking the light that you need to reach the point of contact of your cab with the wheels.
A photo of the clear light bulb.
Photos of the "gooseneck" light fixtures at my cabbing machine and polishing unit. I got them at IKEA for under $10.
A very important light is the one above my cabbing/polishing station. It is a two bulb flourescent fixture on the ceiling mounted parallel to the cabbing/polishing station. It is used to check for mini flat spots on the surface and dome edges
of the cab. It is also used to check for a flat spot on the top, center of the cab.
If you hold the cab away from the "gooseneck" light, but under the flourescent light with the long dimension parallel to the light fixture you will see the reflection of the bulbs as two parallel lines.
Here I'm holding the cab with the reflected lines at the top of the cab.
Here the reflected light is at the center of the cab. Notice that the lines are parallel to each other.
Here I have rotated the cab further away from me and the reflection is still two parallel lines.
This indicates that the cab has no mini flat spots about its surface and no flat spot in the center. An ideal sanding job!
Mini flat spots will be indicated by distortions in the lines as you rock the cab towards or away from you . Unfortunately I don't have a photo to show this.
Here are some photos that will show a flat spot on the center of the cab.
This photo shows the lines are parallel at the top of the cab.
This photo shows that in the center of the cab the lines are not parallel to each other as was shown in the first cab.
As you continue to rotate the top of the cab away from you the lines will again become parallel.
This same effect will occur anywhere on the surface of the cab where a flat spot exists. A wavy, rippley line indicates multiple flat spots.
Here is another before and after series of photos to indicate the flat spot in the center of the cab.
Parallel lines at the top.
Lines not parallel in the center.
Lines parallel at the bottom.
I went back to the coarse sanding (worn 100 grit S/C belt) step and sanded above and below the flat spot to gain the rounded contour that I wanted.
A photo of the corrected dome.
I also use the "gooseneck" lamp with the clear bulb to detect ripples in the girdle of the cab. By holding the cab edgewise to the light and watching the reflection of the light as I rotate the cab I can readily see distortions in the girdle surface.
To make this system work best you have to be at the latter stages of the sanding operations so that the surface has started to become a little shiny and they will start to reflect the light better. You can wet the surface and see some of the larger distortions in the surface but not as well as in the later stages of cabbing.
The final step when you are really confident that you have all the scratches out is to hold the cab under the flourescent light and slowly rotate the cab and look for scratches. Maybe they will be gone! Now turn the cab clockwise 90 degrees and look again. OOPS, there they are!!! I always do each sanding step by sanding in the same direction. This way I can readily see the scratches when I rotate the cab.
I hope this was helpful.