water or light stress leaves curling

This plant is under a 24/0 400 HPS about 3 feet from light. Recently transplanted from 1/2 to 1 gallon, during the same time I took it off the 1000w hps and put under the 400w. Im thinking this is problally too much light? Or the transplant and underwatering during that period. The room stays between 60/80 degrees. Humidity 40-60. Plant is healthy green and virgourous. Opinions on what is going on with the curling leaves.
 

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