Looks like light bleaching to me. I would raise your light up, say to about 18-20" above the plants. If you have some cal/mag supplement, mix a teaspoon in 1 quart of pHed water and mist them with it once a day for 3-4 days. That will help the leaves recover.
Also, when taking pictures for diagnostic purposes, take them under natural light so we can see the true color of the leaves.