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seeds Seedling Cotyledon Dry and Browning - Grow Light Issue?

I believe my situation may be the same or similar to these posts which seem to suggest that the grow light is too intense or hot:
I started my seedlings about two weeks ago but changed out my existing old fluorescent lights for a Spider Farmer LED SF-2000 which is a lot more powerful. I noticed today that the cotyledons of a number of the seedlings were getting darker and had some dry brown spots with curling. The seedlings were started in rapid rooter plugs and had been kept with their domes on until I received the new light and set it up two days ago. I used to keep the old fluorescent light only several inches from the seedlings but with research and reading the SF-2000 should be kept around 18" away. I have since today moved the light up to about 24" and covered the seedlings with their domes again which I am not sure is needed. I should also mention that I ran the fluorescent light 24 hours but have now set the new LED light to 18 hours per day. I do not have any reflective sides on my grow area at the moment.
Below are some pictures which are actually hard to get as the lighting is so strong. Should I worry about this at all, move the LEDs more or adjust the total time without light? Thanks.
EDIT: Also not sure why my images that are uploaded are rotated sideways.







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Id say its definately because of lights beeing to intense/close. My seedlings looked just like that, some even worse, before i raised my lights. They recovered quickly and most of the bleaching went away too. Also, when i suddenly removed my dome i noticed some reactions of my seedlings as well. Im no expert but i suppose that any sudden change of the environment of plants beeing that young will cause some sort of reaction at least to some degree. Just let them do their thing and let them adapt. I didnt have to raise my lights much at all as light intensity drops very quickly, a 1/4 ratio when distance is doubled if i recall correctly.
From what i can tell it seems that you probably raised your light enough but the only way to know is to wait and see. Also, i suppose the dome will cause the light to scatter and become less intense. So i guess only way to really know if light is raised enough is to remove it. They will be just fine!

Interesting side note: Some people argue that this 1/4 ratio only really can be used for point sources of light and that this rule is inaccurate for led fixtures with many bulbs. Sounds logical. I really doubt the difference would be that big though. Any way i just found it interesting and wanted to share.


Extreme Member
Great!  Taking off humidity domes all-at-once instead of gradually can cause stress sometimes and may have played a part here at the begining, particularly with the sprouts with the canoeing cotyledons.  It won't hurt anything to move the light back even a foot farther until your sure they're happy and a little bigger and then start moving it gradually down again until you find just the right distance. I can't imagine them stretching under that light even at 3 feet!
Good luck!
EDIT:  Good post ChrisH.  You snuck it in on me while I was typing mine or I might just have said "what he said."