LEDgardener

I was hoping that my pair of Atreum 288.2 3000K boards would grow from seed to harvest; spectrum charts indicate there is plenty of blue even at the lowest power. However, even at a meager 100W, the seedlings began to bleach with some burning and curling at the tips, and basically wouldn't grow (heat was not an issue). They greened up very quickly when I replaced the Atreums with a single 3500K Bridgelux GEN2 2-foot strip.

Now, I've grown seedlings just fine with blurple LEDs and much more initial power. So, after a bit of research I believe that seedlings cannot handle the intense green and red provided by my Atreums.

It could be I didn't provide enough darkness, though I did try a few dark cycles without any discernable improvement.

Now that the seedlings are beginning to establish, and seem starved of light, I've put the Atreum's back on and they appear to be responding better.

Has anyone else had this problem? Is there a specific point of cannabis development at which quantum boards @3000K can safely be applied? Does this issue occur at 3500K or 4000K? Am I missing something?

I was wondering why my seedlings looked unhappy under 5000k, and 3500k, so I put them under 2700k to see if they would like it better.

Then I did some calculations and realized that the 75w I was using to light 2 square feet should create a ppfd of over 700. I removed the mylar and raised the light so it covered about 4 1/2 square feet and the plants started growing fast. I think even 300ppfd is a bit much for seedlings.

Got 3 x 3000k Vero29 COB (about 150w, passively cooled) and the chili seedlings/chilis are developing waaay slower than under my old viparspectra 300 blurple but they are healthy and green, except the varieties with anthocyans for light protection, they are deeply purple as they should be. I have since upgraded the Viparspectra with a 50/50 mix of 400xSamsung LM301B 3000k/5000k Diodes (reused the original viparspectra driver and case, so about 110-120W, actively cooled) and seedlings are exploding with really tiny internodal distances. May have gone a bit overboard with the 50/50 mix there

Keep in mind that the efficiency of the passively cooled and quite hot COB is way below the refurbished Vipar with actively cooled and slightly underpowered LM301B (on a relatively small surface)

As uncle highlighted, you simply had WAY to much light on those seedlings.

One 2’ Eb gen2 only produces 13.6w at nominal power. Compared to your 100w setup, it’s clear you were simply over powering them.

Xenophon, you don't need to focus on overall power, but rather power per area (and even power x area x time since seedlings get light for 2x longer then flower, so they can reach the same DLI as a flowering plant with half the light).
I dropped from about 40w per sqFoot down to 20w per sqFoot and things got significantly better. Actually the drop is even greater since I took of the mylar wrap so the light probably spreads 25% more. Even 20w per foot is probably way overkill, when you take time into account.
Seen quite a few experienced growers who benchmark each clones performance under different light intensities when they get new strains. Hoping to get some very low power drivers so I can do minor testing on my keepers as clones and early veg.

Power + area + TIME
The often forgotten and underutilized aspect of seedling lighting is time.
It’s good to think of it that way because power is only part of the equation.
I could even argue for power being the least important because given enough time, under an even blanket of light, power becomes less and less a factor as the light cycle for seedlings is often extended.