"are you very sure that projectors utilize that form of lighting today?" Red

I believe it was when celluloid film was catching fire.

BTW, Red:
I heat my home with a wood stove.
Sometimes I like to clean that stove, though it's quite hot.
I used a synthetic bristle brush on it, and melted the bristles down (too bad, it was a nice broom).
Now I used a simple straw hand broom, and it works very well.
I'm not saying celluloid doesn't pose some flammability risks. But I suspect some other materials with similar properties (transparency, & flexibility for example) may be nearly as flammable, or perhaps even moreso.