Yes, a light-sensitive material could show relative brightness differences, but photographic paper is likely simpler than film or instant film for a basic test. You would tape the paper to the screen, expose it briefly, then develop and fix it under appropriate darkroom conditions. The resulting density may give a rough map of brighter and dimmer areas.

That said, the more straightforward and reliable approach is to use a light meter and take readings at multiple points across the screen. Since you’re trying to evaluate brightness uniformity, spot measurements around the center and edges will likely be more practical than working with film.

So: photographic paper may work for a rough visual check, but for measuring how even the illumination is, a light meter is the better method.