I recently bought a type A desk lamp with a 100w max for a small aquarium. I have a 100w Type R bulb left over from a Type R lamp meant for aquariums originally and I was wondering if I could use the Type R bulb in the type A desk lamp?
I did try it out for a half hour and I thought I smelled burning plastic from the top of the desk lamp and noticed it was a bit warm. The desk lamp is brand new, so it could be that too. Just want to make sure I am not creating a fire hazard here.

If a fixture is designed for a lamp, an R lamp should not be used.

Light and heat radiated nearly 360 degrees from a lamp.

An R lamp concentrates all light, and heat in a much tighter pattern.

Hence the smell of plastic.