Too OP too fast.
Light magic as in photons, not holy is an interesting premise, but with isekai and modern technological knowledge it would be way better if MC actually had the potential to JUST generate light (which by itself would be equivalent of being a walking flashlight, evolving into walking AA seeker light from WW2 era - nice, but kinda useless like people assume), and to actually use it for things like combat/communication he'd have to use technology.
So no gravity defying light arrows, lasers from the fingertip, optical camouflage but literally a glass cannon.
Make him get some lenses for his first gun. Make him look for a pure ruby to build a ruby laser. IDK, maybe even some sort of optical telegraph? Endless possibilities, instead of beach episode they could make a tanning salon episode.
Could make him physics student to explain the knowledge, and show him trying to handle it with medieval level technology.
Want to make your laser curve? Sure, let him find someone withh gravity magic.