Light burn?

Possibly. The nodes look super tight, but it's a bad angle. This is an autoflower, i assume. So, 20h and full power may be too much. You only need 25-30watts per sq ft when running 18h a day and 20h you need 11.1% less than that, because it is 1/9th more hours per day. More is not always better. 35-40 DLI is all a plant can handle in ambient co2. Whether you get there in 12 hours or 20 doesn't matter one bit. Giving more than that absolutely causes problems. The exact value varies by location due to more than onen variable being key, but ambient co2 is the biggest factor. temp and rh (resulting vpd) matter, too Good chance you are gassing it too much with light. Would need more infor to be certain. I don't think it's too far off, or the visible symptoms would be worse. Light damage can take a long time to show up if it's only slightly too much, or occur really fast if torching it. The whole gambit is possible. ------- Also you should not be picking a volume of water to give it. you should be giving the volume needed to get the job done. 1.5L is fine if it gets the entire thing wet and really bad over time, if it does not. Always water until it's fully wet and a minimal runoff out the bottom can help verify that. if soilless, you should get a 10% runoff religiously. Wait for top layer to dry and repeat. Keep it simple. The volume depends on how long you wait between and what constitutes your soil. You should never allow OCD to choose the volume of water to give, it simply isn't your choice.