Light distribution

Using two Telos grow lights doubles the PPFD in the middle, where the lamps' footprints overlap.

You can clearly see that it's the light distribution. It's always more powerful in the center. There's nothing to worry about. They look great.

I think you could assume that it could be both. Since you are using two lights, then your spread will defiantly be different in the middle vs right under the light. So yes, the light could very well be the culprits. But, you cannot throw out the chance that it is a strain as well if you are running different strains. They can totally behave different. If these are all clones then you can safely say it would be the light. I hope this helps.

Judging by that earlier picture https://bucket.growdiaries.com/static/post/photo/129880/8219457_262edd163b7b9327c3376c81f1f76ced_big.jpg I am inclined to agree with you that culprit is a light distribution. I see that previously all plants were uniform green and that you have a rectangular gap between 2 lamps right above where the plants got lighter green color.

from what I can tell it is more than likely genetic difference in varieties