Top leaves curling upwards

Greetings RIU,

I have a girl who is about 4 weeks into flowering, and I recently switched to a 400W HPS a couple days ago from CFL's.

I noticed that her top leaves are curling up and I was wondering what could be the issue. At first I thought it was heat stress, but I have a fan pointed at the reflector and I also have the room open so it can get fresh air.

I took the temperature underneath the light at the top of her main cola, and they are no more than 84 degrees(F). The room is about 82 degrees(F) as well.

Could this be heat stress?

How far is the light from the top of the plant?

If it's just the top and you just recently switched the light you can almost guarantee it's light/heat stress.

Its about 13-14 inches, and I do not have much room to raise the light any further. Is it possible for this to subside? Or will it only get worse?