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From everything Ive read on multiple forums, you want your light as close as possible to your plants without burning them. Ive read about the "arm test"...if your arm isnt uncomfortable then your plants will be fine. Many people suggest to get a cool tube so you can get your plants even closer and Ive even read posts that say you should always keep your plants no further than 24" from your light if possible. My results do not show this.
I have a small grow tent for my plants that are vegging, and up until a few weeks ago I was using CFL's for veg. I would get them as close as possible to the CFL's and they were healthy as can be. I switched to a 400w MH and ever since my plants became sick looking. Tips of the leaves turning brown, some leaves curling up, some wilting, etc. The plants were close to the MH but not so close that my arm would burn or even become uncomfortable. I tried everything I could think of including flushing multiple times with ph'd h20 thinking it was nute burn, but nothing helped...except moving them out of the tent and into flowering (which is quite a bit farther from my 600w HPS). Those two plants bounced right back.
So a few days ago I moved my grow tent plants down another 2 ft away from the light and they bounced right back as well and look as healthy as ever. That is the only thing Ive changed, temps still right at 75-80 like they always have been, humidity the same, etc...only difference is they're not as close to the light.
So my question is, did I just learn the hard way that plants can actually have too much light?
I actually have one of those already, what is the ideal temp for the leaves, < 80? That makes sense too because the leaves started becoming more pail which made me think they weren't getting nutes because of nute lockout. It just surprises me that a 400w MH 2 ft away could be too much light...I could understand if it were a 1000w light.
No I dont. I have all the vents open on the bottom of the tent, and a 240cfm duct fan sucking air out of the top of the tent to keep FAE. Its a 36" x 20" tent and 63" tall, I don't really have room for a fan inside the tent with my plants in there.
Sounds like ya need a bigger tent. You should be making sure there is air blowing around the canopy. This helps cool off the plants, as well as prevent humidity build up in the canopy. This in turn helps prevent things like powdery mildew.
-------------------- Dude she isn't as young as she use to be.
No room for a bigger tent unfortunately. The tent is inside of a big walk-in closet, and the rest of the closet is my flower room. They're doing good now that they're away from the light though, hopefully this won't induce too much stretching.