Did you splash any nutrient solution on those leaves? If so, they may have burned a little. No, this isn't the "water droplet acting like a magnifying glass" myth... It's just that when some nutrient solution gets on a leaf when it's under the lights, the stomata are wide open; they essentially gulp up a big dose of fertilizer through their leaves. If it's more fertilizer than they need, it can cause burning.
Can you show a picture of the whole plant?