NEASEMOanswered grow question 4 years ago Use caution with foliar sprays while the lights are on. The droplets can create a magnifying effect and focus the light to a point on the leaf, burning it. Also, if you're trying to introduce nutrients through the spray, the lights and warmer temps associated with them can cause the spray to evaporate before the leaves can absorb it all. If you do spray with the lights on, do it within an hour of the lights going out. Be aware that spraying will increase RH for a short time as well, so you may have to factor that in.