Get rid of the humidifier. You need a de-humidifier.

Whats happenning is the humidifier is brining the moister in the air to an all time high. I would hate to see how high. With that and plants transpiring I bet the water drips down the outer walls of the room.

With that being said guees what ? moister is collecting on the leafs. The plants can not transpire enough to dry out and when the lights come on Guess what again ? Even though you can not see it well your leaves are covered in moister when the light come on and that is the burn on the leaves. The light doesn't even have to be right on they when they first heat up under the light. Just the heat will cook them.

Please lose the humidifier !!!!!!!!!!!!!!!!!!!!!!!!!!!