Remember what they say down south in summer? "It ain;t just the heat, it's the humidity" lol. The relative humidity is low near the light bulb and the plants don't have to be physically HOT to show heat stress- they are also transpiring rapidly in that intense light and drying out quickly. Tying them away from the light, keeping up with watering, and even adding humidity to the room are ways to combat the heat stress. Be careful not to overdo the extra water/humidity. Next time consider flowering at a shorter stature so you don't run into height issues.