Moral of story....never be in a hurry and do it right the first timeYou are right, of course, that one of those was a plain incandescent light fixture with reflector. However, it had adequate clearance and was theoretically safe while it was clipped on the roosting box. That illusion of safeness faded when roosting chickens knocked the clip loose. I was in a hurry setting it up, like I said, and took a risk that chickens would not knock down the hot lamp. Won't be making that mistake again!
FWIW, that fixture is now in the trash and will be replaced by some of the other wonderful tips suggested by others in this thread: Mylar bubble wrap, Cozy Coop flat panel heaters, and oil-filled radiant heaters on low temperature setting.