Back when I ran AD&D I kind of stumbled into good bits of DMing from time to time. Not always and I didn’t really know to weaponise them as much as I should have, but I had my moments.
Potions were one of the first things, where I’d write in the Dungeon Master’s Guide what colour each potion was and the group would have to figure out what they did. They could identify them or test them on someone (to help this, each potion had 1d4 uses).
Anyway, this is about light. Ages before “Okay, what does that look like?” as a common mantra, I would ask that about people’s magic. Light and Magic Missile were my favourites. I didn’t really know the limits of Light and I didn’t really care to. When a player cast it, I asked how it was created and what it looked like. For one player they would have the tip of their staff glow. Another had an object he touched, which could be a players’ sword or someone’s eyes. One had glowing fireflies around them and some would just say, “I don’t know, it just gets brighter” and you know what? That’s fine too.
Magic Missile would often get aspected to whatever the theme of the magic user tended to be. It could be a lesser version of their more favoured spells (a little fireball, for instance). Flying skulls was a favourite. Most of the time they’d be some kind of glowing balls of light or fire.
Even in a more traditional game, it’s definitely worth asking what the special effects of magic look like. It also means player innovation can shine with problem-solving using the minor differences their special effects might bring, like the magic-user casting Light on someone’s eyes.