Light distance: how close it to close ?

Get that shit close. Get a lux meter. It's a good investment, trust me.

 

My 400w in a cool tube. I had it about 8" away. Would of had it closer but needed the speared

 

Yes. Here's a bud growing up against the lens of a 1kw air-cooled Raptor:


The distance you have to keep your light from your canopy, depends on how much you can cool your canopy.

 

It also depends on how much light your bulbs put out there is DEFINATELY such thing as too much and a plant that close to a 1k is loosing potential yeild. 8 to 10 inches away would be better.
It's not just about heat.
It's about par pur lux and lumens

My latest creation...SOUR DEISEL, STRAWBERRY HAZE first run to test before the gorilla glue #4 go in!
SOUR DEISEL, STRAWBERRY HAZE & GHOST WRECK

 

I keep my lights about 4 to 6" from the tops of my plants...

A good test is to put your hand between the light and plant top, it should feel like a warm summer day on the back of your hand, and when I'm faced with a new light, that's how I judge just how close I can get the light to the plant tops...

 

See I can put my nuts on the cool tubes jake without any pain back of your hand whatever... but anything less then 8 inches they burn. I also find they go pale yellow and bleach out I tend to try stick at 8 or 9 to 14 inch above canopy level.

My latest creation...SOUR DEISEL, STRAWBERRY HAZE first run to test before the gorilla glue #4 go in!
SOUR DEISEL, STRAWBERRY HAZE & GHOST WRECK

 

That bleaching or yellowing because the lights are close is due to a couple factors..
I'm in coco running 1200 ppm @ 5.8 and use Co2 in my chambers so I don't get that bleaching on my leaves..

Maybe the combination of high nutrients, higher temps (82* to 84*F), and the Co2 is why I don't get bleaching.

 

Very possible jake I've not narrowed it down far enough yet to disagree or agree.

My latest creation...SOUR DEISEL, STRAWBERRY HAZE first run to test before the gorilla glue #4 go in!
SOUR DEISEL, STRAWBERRY HAZE & GHOST WRECK

 

I agree

 

I've learned that, with my hoods, I can back off the lights more than I once thought (and used a light meter to make sure light was adequate). I had a 400w that I used to keep very close. Directly under it, I would always get very fat but airy buds and foxtailing. I've backed off to about 12 inches from the glass, and I still get between 50k and 80k lux to all parts of the plant with better results. It also helps get a more even distribution.

 

Correction: 12" from the bulb, 6" from the glass.

 

I have a Quantum Board Cob combo and wondering the same. Im at 24" in 3/4 wk of flowering.




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Look at some of these commercial facilities. They run 1000W as high as 10' above the canopy and get great yields with dense buds.