It is fairly typical to set up an inspection light on a tripod or stand which points at the panel, while a detailing technician is working on it. They may also use hand held inspection lights, so they can continuously check their work.
Good lighting is essential for paintwork correction because of the nature of many of the imperfections the technician is trying to remove. Micro-Marring, micro-scratches, or collections of micro-scratches can be seen because they catch the light differently to the rest of the panel. How much they show up depends on the intensity and direction of the light. Without inspection lights, it is possible to polish a car and have it look perfect, only to find that a couple of hours later, when the sun had moved and light is shining from a different direction, it reveals many other issues.