Is this heat stress?

What's happening here? Are they dying?

Your plants look perfectly fine, some browing like that is perfectly normal so don't worry about it your just worrying too much about your plants. Let them grow. Don't worry about it unless it gets drasticly worse.

I agree with last post.Iknow that it is hard not to worry but most plant get a little browning. If you are ever in dought higher lights for a couple of days.Also if u are growing in soil then flush em get rid of any salt build up nar worry ya self be cool and let nature take its course If it gets worse then send another thread it may be heat or nutes.Also becareful when watering try to keep any water of leaves i've seen browning of leaves through nute burns.