lighting
After 30 years in the Design Studios of General Motors working with clay models in various stages of refinement from "rough as a cob" to slicked to a high gloss finish and covered with a "stretchable vinyl paint film called Di-Noc here's what I learned.
The slicked down clay holds the "paint" to allow one to see the reflected light from the overhead lights. The lights were tube type flourescents covered with diffuser panels mounted on a grid of metal supports. The grid created horizontal bars that were reflected in the surface. The variations in the surface, clay, made the horizontal bar move up and down, diminishing or expanding depending.
We sometimes oiled the "paint" to add more reflectivity to better see the surface, which would be similar to a wet paint coat.
The ceilings were far above the cars and slanted toward the windows which were full room length and about 15 feet tall.
So what's that got to do with a paint spray booth?
Possibly nothing, but here's what I came up with.
Spraying panels or surfaces that are vertical are more difficult to see the reflections. By having the lights directly overhead you don't get the light reflecting in the surface as you would if they were further back and high up, say at a 45 degree angle. Spray booths are necessarily confining in order to contain the vapors, so the lights are closer than optimum. Having full length light tubes will create the horizontal bars needed to read the surface. I would make them as continuous as practical...8 footers rather than two 4 footers in a row.
Horizontal panels will reflect the light directly overhead more readily. You can experiment with a shop light that's hanging in your shop and a high gloss panel like a piece of Formica or a finished cabinet door. Determine the angle and distance from the light which best shows the light tubes reflected in the surface.
Your body may cast a shadow in the path of the light, so be aware of that as you would stand in front with a spray gun...
more experimenting.

bill