If your marijuana leaves become curled, dry, and brittle…..your lights are too close to your plants. You may notice the lights actually leaving burnt spots. If you foliar feed(Mist) before or during the lighting phase the droplets may have a magnifying effect as well and could lead to some damage spots. You can also get these spots if you’ve got some refractive element focusing the ligh(think magnifying glass). An easy way to tell if your plants can handle it is to simply place your hand under the light just above the plant tops. Is your hand hot? Can you stand to keep it there? If it starts feelin to hot than your plants are going to more than likely receive stress as well. I try for 74-78F at the canopy.
Generally during times of stress, like introducing new seedling or clones to light, you do not want to punish your plants further with overwhelming lumens and heat. Let them establish their rootgrowth and work them up to a bazillion lumens(lol). Maybe start your lights at twice the height to reduce the lumens and heat. Then drop them down when the plants are showing active growth. As your plants grow towards the light(inches per day), keep close watch, er uh….i mean feel!