Going in the other direction, if you need it, there is a terrible "key-light" you can get, at hardware-stores or key-shops, where you slide a flat metal key inside this black plastic thing that looks like a photon with a cape on.
Adhesive inside holds your key and now you can press a button on the black plastic thing and have light come from a small lamp that points right down your key.
These key-lights suck in general, but if you need this exact function they're fine!
I have a big old kawasaki motorcycle where I wanted a one-handed illuminating key, but did not want another item attached to the key, banging around and so forth. This crummy "key-light" ended up being the best solution for me.
But hanging on a key-chain, you've already gotten good advice!
I use Photon's on my average keychains, I bought a bunch of them years ago and I'm still trying to "use them up".
- Thomas