Hi! No, like I said they are grown indoor (soil). Hmm... Could they been "sunburn" by artificial light? Sounds crazy, but most damaged leaves are in the most bright area. Those around the light are fine. The light is not that intensive, its a fluorescent light 2700K (flowering spectrum) with 220W combined power.

I second the sunburn look and yes it's possible indoors (smile). Are these leaves getting too warm? Your spectrum is correct for flowering. Perhaps you have a nutrient deficiency. Good luck with growing these gems indoors!

Depends on the kinds of lights you use. Some get hot. The ballast on fluorescent also may get hot

No, you can easily hold a hand right on them, feels just warm. And no ballast there. 2G11 tubes, if that matters...

Well, whatever it is, it isn't disease. So, the bottom line is that this is a mystery you'll need to resolve in order to avoid the same thing occurring on other plants at some future time.