Leaves starting to curl up

This phenomena is referred to as “praying” and is a result of the plant trying to protect itself from what it believes it a blazing, unrelenting, sun. In an outdoor setting cannabis receives light from the sun, which is constantly moving across the sky from dusk til daw. As the sun moves “over” the plant, the plant’s leafs receive a full dose of sun if they are flat and facing up towards the sun. When the plant receives a combination of too much heat and too little humidity, the plant folds its edges up like that in hopes of providing shade to part of the leaf that would only typically be exposed during the middle part of the day. Unfortunately, with a stationary light-source this action by the plant is pointless. If the heat isn’t reduced and the humidity raised soon, the leafs will continue to become a purplish/red tone, they will become coarse to the touch, and only the very middle of the leaf will remain green as they continue to pray. The branches will all turn a reddish color also and of course the plant will stop growing due to stress... I think:)

The leaves are beginning to "taco" which is a sign of heat stress. Since the leaves aren't burnt I wouldn't say it's from the light it's more than likely from poor air flow or low humidity. Hopefully this was helpful and remember "Happy Growing and Free your mind one puff at a time".

they need some cal/mag or Epsom salts. you could make a spray with the Epsom salts and spray the foliage and probably clear up

Yes that simply means they're is not enough moisture for the plant. Water more frequently and try to increase the humidity. 🌱👍

So just going off the one photo....and not knowing your stats, lights/heat/humidity/ nutrients etc.. I'd guess somewhere along the lines of heat stress from the lights(maybe too close), bad humidity (most likely too low, but the reverse can be true too), or root troubles(wrong soil ph, rot, bound). See if any of those apply and try to correct what you can. At least they aren't burnt...so they can heal. Good luck. ✌️