Help me calculate proper distance from the plants

athomegrowing

athomegrowing

Well-Known Member
I have a 4'x2'x6' tent with 3 75 watt cree cobs from rapidled. I am having trouble dialing it in without tools, and was wondering what an appropriate distance to start at. I'm currently in flowering, but suggestions for flower and veg are appreciated.

Currently I'm at 30" without the reflectors, without calculating it I'm not sure where I should be for optimal placement.

I found this calculator, if you know how to use it you can answer my questions: http://dev.edman007.com/~edman007/pub/par-dli-cal.html
 
athomegrowing

athomegrowing

Well-Known Member
LED Cultivation said:
Should be safe bringing them to at-least 22". More important than a calculator is making sure you've got your environmental control dialed in. If temps, humidity, etc. - are on point, you should be able to bring them closer. Its not about getting them as close as possible, but 30" is pretty far away.
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with or without reflectors?
 
LED Cultivation

LED Cultivation

Active Member
athomegrowing said:
with or without reflectors?
Click to expand...
Your best bet would be to set them up in a pattern where you think the light would spread best at, and place down a white piece of paper underneath them. Lower them until the spread of light looks appropriate. You can test this with and without reflectors, which should change your idea for what you think will work best.
 
athomegrowing

athomegrowing

Well-Known Member
LED Cultivation said:
Your best bet would be to set them up in a pattern where you think the light would spread best at, and place down a white piece of paper underneath them. Lower them until the spread of light looks appropriate. You can test this with and without reflectors, which should change your idea for what you think will work best.
Click to expand...
Thanks. I fucked up, and REALLY damaged some plants and now I'm a bit nervous that it will happen again.
 
LED Cultivation

LED Cultivation

Active Member
athomegrowing said:
Thanks. I fucked up, and REALLY damaged some plants and now I'm a bit nervous that it will happen again.
Click to expand...
COBs are very strong, especially driven at 75 watts. You'll notice mounting distance is more about spread of light than anything, once you've got your environmental control dialed-in.
 
Airwalker16

Airwalker16

Well-Known Member
athomegrowing said:
with or without reflectors?
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Reflectors cut 8-10% of your total light output they just found out at Cutter/timber/or rapid I can't remember who's IG I saw it on, after doing a bunch of testing.

Also, in a tent, theyre an absolute waste. All in all, only reason you should ever use any reflector is a glass one, and that's so you can be IP65/67 waterproof commercially rated. And that don't concern us DIY'ers!!!
 
OneHitDone

OneHitDone

Well-Known Member
Airwalker16 said:
Reflectors cut 8-10% of your total light output they just found out at Cutter/timber/or rapid I can't remember who's IG I saw it on, after doing a bunch of testing.

Also, in a tent, theyre an absolute waste. All in all, only reason you should ever use any reflector is a glass one, and that's so you can be IP65/67 waterproof commercially rated. And that don't concern us DIY'ers!!!
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o_O
You just like to roll bareback so you can claim Disney Land #'s that will never be attainable in a true commercial grow operation.
Be careful you don't burn down mommies basement :lol:
 
Airwalker16

Airwalker16

Well-Known Member
athomegrowing said:
Did he fuck your girl or something?
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He acts like it. I felt my reply was pretty relevant to the thread. Don't really see any reason he'd be a dick to me for it. But as he said, he gets a "kick" out of it. So I guess it doesn't take much more than me just posting. Sometimes I don't even have to do that.
 
welight

welight

Well-Known Member
One of the advantages of COB at high power is to run them at higher hang heights and then use dimming to regulate photons. almost without question people start these at lower power and ramp them once the plant has had time to adjust, if you have reflective walls I would not use reflectors as that is intensifying your centres
Cheers
Mark
 
wietefras

wietefras

Well-Known Member
Airwalker16 said:
Reflectors cut 8-10% of your total light output.
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And that's when they are perfectly clean.

Besides, that's just the light lost on the reflector itself. You also need to hang the COBs with 90 degree reflectors about twice as high as bare COBs to get the same light distribution. Hanging the fixture higher also means that mor of the walls will be lit up and therefore you lose more light on those walls.

Years ago (2016), Malocan tested reflectors in his 4'x4' tent and measured 15% less light over the entire surface with reflectors compared to no reflectors (and closer to the plants).

Another way of lowering the hanging height is using more light points. Using 4 COBs points instead of one big one (or a single QB) also means that you can hang the fixture lower. Half the height actually and therefore cut wall losses in half.

If you want to calculate a good starting point for the light then take the distance between the rows of COBs and 2/3 of that distance is a good hanging height.

So if you have one COB in the middle of a 2x2 then the hanging height would be about 16". If you hang 4 COBs over the same space the distance between the COBs will be 12" and the advised hanging height would drop to 8". ie twice as many "rows" means the height is cut in half.

In your case I would go with about 16" to have the single row of COBs spread their light out over 2'.
 
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