Heat, light stress? Or both?

4 week old. Soil grow. Temps can get high around 38 degrees Celsius( taking care of that. Leave ac on in room during hottest part of the day. Brings tent to 28 degrees) Humidity around 60%. Enough water and some nutrients.18/6 Marshydro TS1000 LED 150w, about 50cm above tops. Some plants have curled leaves some don't. Some higher some lower. Seems random. Would think temp stress but others in the tent seem fine. Light burn maybe but like I said some have it some don't. Thoughts?

Looks like heat stress to me to be honest. I had light stress on mine last grow and it never did this. It stunted the growth and started to fade to yellow before I got it straightened out, but never had the leaf curl. I think the best temp is going to be around 20-30 degrees Celsius during the day and 17-20 during the night. Your heat looks a little high. Are they different strains? Some strains handle heat better than others for sure..

Heat stress.
FF

Light stress will show same, but with bleaching as well...tips or whole tops.
Good luck.
FF

Try keep temps around 27. Thats leaf taco from heat stress

as has allready been stated but cant hurt to have as many opinions as possible, clasic heat stress

Run your lights at night instead of during the day to reduce temps for no cost.

Have upgraded the extraction fan to a centrifugal type fan.
Just a slight upgrade

Have negative pressure in tent and temps are now between 26-28 degrees.
Have lights set for off at hottest time of day. Air conditioner on in room when temp hits 35 outside to keep temp down.
Cheers guys.