Radiant heat is different that just ambient room temp. I have had heat stress with temps in the low 70's. It causes leaf margins folding in or "tacoing", leaf tips curling upward, chlorosis (bleaching), necrosis (brittle leaves). It is usually most apparent with the uppermost leaves and leaves most exposed to the light.
Imagine a blacktop parking lot on a bright sunny 80f summer day. You can be sure that surface is hotter than 80. That is radiant heat and the blacktop is your leaves.
This type of heat stress can cause to plant to "shut down" and stop feeding. This results in what looks like nutrient deficiencies which people attempt to fix by feeding which compounds the problem.