In the spirit of sharing experiences, Here’s a pic of what LED light burn looks like.
I have done a lot of research regarding how many umols I should be covering my canopy with. Firstly, it’s very seldom you find growers with the instruments to back up what they’re saying. A distance figure means little when everyone is using different lights. Even the manufacturers distance rating goes out the window when you’re using more, or less lights.
The best info I’ve found, stated 700umol/m2/s as the golden number for LED. This one plant in my current run got a little more than that for about a week.
So, I’ve raised my lights a little and getting an even 600umol/m2/s now. Based on my experience and measurements, I’d recommend 600 as the upper limit for full spectrum LED without CO2.