A pic of the whole plant would help.
Maybe too much ferts or what I'm seeing from your leaves are they got wet when the lights are on or they lay together and transpire and the big light burns them. make sure the leaves do not get wet during light hours. It's OK during dark.
Maybe a hot spot from your light.

What is your runnoff PH ? that's more important. If your container is 3 gallons then you should water with 3 gallons. Yes 3 gallon. Pour it through slow. This makes sure it is watered to the bone and then it needs to dry out good and repeat. Watering too often and with too little is a common problem. The soil just doesn't get wet to the bone. Small amounts don't flush bad things out and build up fert salts
LOC NAR on probation Reviewed by LOC NAR on probation on . Please help me ASAP!! Diagnoses form filled out with pics! Serious!!! They started off just fine all through veggatative growth. They were in veg for 5 weeks then switched to flower they have been in flower for 4 days and on day 2 they started to show browning on the older leafs and it started from inside out, now some of the leafs are curling up/in. A few of the leafs turned all brown but they weren't crispy. I hand water and I think I overwatered causing a phosphorous lockout. Also I think theres a cal mag deficiency and or salt build up. What is your Rating: 5