Ive never been able to light burn a plant with an LED panel. The geometry of the light overlapping kinda fights against you there. After agetting within about 12" from most panels, you are actually losing light intensity because its coming from hundreds of individual overlapping sources that are not at a single point. Go too close and they are not evenly overlapping. Ive had some nutrient deficiency/processing issues with LED's being close that i havent had with other lights, but that isn't at all because there's too much light. Just seems to be something a lot of plants do under light that wasn't created by ionized plasma along side the plants not actually getting the full available spectrum of mixed light because the panels are too close and the chips arent overlapping properly at that point.
It doesn't exactly work like an HPS bulb, where the closer you are, the more light you have. There is a thin red line in there with every LED panel.
That being said ive vegged and flowered plants within 12-14" of 480w LED panels at 100% and havent had issues with most of them. Generally when i flip to flower, ill back the panel off to a couple feet, and let the plants stretch into the light themselves. I usually dont back it off until tips get within like 6 inches of the panel. Ill have some yellowing upper fan leaves, but i end up with a bigger bulk to the main, dense areas of the canopy that way.
Although im probably going to migrate back to T5/HPS this summer . I dont like having to partially etiolate plants when young just because they aren't fans of the kind of incredibly unnatural feeling (even to my own eyes) synthetic light that LED's produce. I actually switched to LED at the same time i transitioned to DWC, so i chalked my nutrient processing issues up to the DWC transition, even though only certain plants had the issues. and i only had 8-10 runs with that setup before i retired from growing for several years. Now that im back growing, in soil, under LED panels, i have definitely formed a different opinion on LED's then i used to have lol.
5.5-5.6 should be fine in coco/perlite for a watering, just dont leave it there through multiple waterings or youll start to develop calcium/magnesium lockouts. I always ran in the 5.8-6.4 range in coco for most plants. closer to that 6.4 range in flower usually. closer to the 5.8-6 area in veg.