Light intensity: Why to keep lights as close as possible

Light intenstiy = Total Light Emitted / ((4 x pi) x (radius^2))

And light intensity decreases by 1/x^2 where x is the distance.

So like if you have 135,000 lumens at 1 foot, you increase that to 2 ft, you it would be 135,000 x 1/2^2 which is 1/4 so basically one fourth of 135,000 = 33,750. Add one more foot, 135,000 x 1/3^2 = 135,000 x 1/9 = 15,000.

Crazy huh? Thats why the top bud always is so big and the bottom ones are smaller, cause they get a lot less light. LST'ing takes that problem away, preventing you from having like 5 feet from the top to the bottom of the plant.

So thats the science behind bigger buds.

I don't get where you got 1 foot as the reference from? The diagram is metric and shows light going down to 25% in the second meter but no change in the first?

Good post, Splifted. :thumbsup:

Wanna see an example of what he's talking about? LOL...

Here's one pic, or you can go to the JOURNAL and see more.

This is a 5 foot plant with big buds on top and liiitle buds on the bottom.

LSTing, SCRoGing or just keeping your plants squat helps to reduce this problem.


Also, make sure you keep them (the lights) close in the veg state too to keep them bushy and short, not stretchy like those lanky f**kers in that JOURNAL. ;) .......Still gettin' good buds from it, though! :baggy:

:clap:

:rasta:

TGF



Edit:

Quote:

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Originally Posted by faithless

I don't get where you got 1 foot as the reference from? The diagram is metric and shows light going down to 25% in the second meter but no change in the first?

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Faithless, I think they are just arbitrary #'s to show the formula...right, splifted?

The thing is if I begin that equation at 2", wouldn't I arrive at a more rapidly diminishing variable? I was always lousy at math though :pimp:

This is what I always preach, good topic. I have my 400 about 4 inches away from the little ones in veg with an air cooled and with the air cooled on the 1000W I go about 10 inches, I could go closer, but I don't want to loos the ft print and I have noticed that some plants can't handle the lumen intensity and the chlorophyll in the bud will become bleached and turn white.
Adieu

Quote:

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Originally Posted by BlueBear

This is what I always preach, good topic. I have my 400 about 4 inches away from the little ones in veg with an air cooled and with the air cooled on the 1000W I go about 10 inches, I could go closer, but I don't want to loos the ft print and I have noticed that some plants can't handle the lumen intensity and the chlorophyll in the bud will become bleached and turn white.
Adieu

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bluebear i love that name,not to get off the subject,but how are able get that bulb so cool.can u tell what Ur grow area and ur fan cfm's because i a small grow cab and i get under 87 constantly. the cab is only 60'' height,15 deep and 29 wide ,so roughly 3.3 sq ft and im running a 400w hps home cool tube with that 80 cfm in-line duct fan.I have it pushing thru the cool tube and out the other side. im trying cool the bulb and exhaust it at the same time and also I have a 80cfm for the intake and 240 i believe for cab exhaust three fan what am i doing wrong.

~smokybear~

I know you addressed this question to BlueBear, but I thought I'd put this out there:

This is just a shot in the dark, but why dont you try hooking up that 240cfm to your cooltube instead and open it up one one side into the cab (kinda like 'mine' in the JOURNAL). Then you could SUCK the air from inside the cab, past the bulb, and out. Then you could put your 80cfm fan where your 240 was and you might be ok.

If that doesnt work, use the same fan setup I just said, but keep the cooltube isolated, sucking cool air from outside past the bulb (not pushing air), and out. Then your 80 cfm fan should do fine as long as the bulb is cool...

Good luck.

:rastasmoke: RastafarI

TGF

Quote:

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Originally Posted by faithless

The thing is if I begin that equation at 2", wouldn't I arrive at a more rapidly diminishing variable? I was always lousy at math though :pimp:

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Yeah, you would, but at 2" it would be a lot brighter than at 1 foot, and at 4" it should be half as bright as it was at 2". I think. You also have to take into account that light isn't projected in a square, either, but that is the basics.

Haha, its been like 2 years since I took AP physics.


Here it is a little more in depth if you were wondering

http://www.ifa.hawaii.edu/~barnes/AS...rsesquare.html

Well, I would think about trying to use that 200 plus CFM fan to suck air out of the cool tube and I would think about putting it in a chain with the 80CFM fan, like keeping the 80 CFM where it is and then attach another vent to the output side of it and then put the 200 plus on it to pull, and have both working together, might work. On my set up I use two C24 cabinets put together which gives me a FT print of 38 inches d 47 W and about 60 high. I have an air cooled hood in there and have a 172 CFM Vortex fan pulling from the top of the hood out under the house into the filter and a 90CFM fart fan blowing in the side of the hood and this acts as my out take as well. On the bottom left corner I have another 90CFM fart fan bringing air and on the bottom left I have a 240 CFM Dayton bringing in cool air from outside. This keeps my box around 78D. I now have the 1K light in another room with another 1K with these parabolic hoods which are huge, 4 FT diameter, that are completely open and with one light going I can achieve the same results in the winter with the open bulb with no cool tube or aircooling or even a out take for that matter, but in the summer I will def have to reconfigure with an AC and possible air cooled hoods.
Now I have the 400W in the same cab with the 1K gone and I have taken out the 240 CFM fan and turned off the 90CFM fart fan that pushes into the hood so I only have a 90CFM fan on the bottom left and the 172 Vortex going and it is fine. I could put that hood with the 400w on my tummy and go to sleep I think it is so cool. Sometimes I can't even tell it is working right because it is so cool, but my plants assure me that it is with their growth.
Some key things for me have been a active intake that comes from the out side and the aircooled hood with the top vent to suck the heat right out of the top of the hood along with a good fan. The vortex 172CFM works twice as good as the Dayton 240 and that is a point to always consider, CFM's really are only as good as the brand of the fan IMO.
Hope this helps some, go a head and feel free to ask any more questions.
Adieu

sweet! I will definitely do that bluebear and thanks again:thumbsup:
green fog thanks also great info from both of ya

oh! here the set up,check out my current threads heres one I have two going


http://boards.cannabis.com/showthread.php?t=86604

damn that 'you must spread rep' box. DAMN IT!!!
After all, you and the Bear are always posting informative stuff.
DAMN DAMN DAMN.
nice one.

Just google 'Inverse Square Law'

The distances are not measured in linear feet, but total area of illumination. distance doubles, light is quartered (same total light, just spread over 4 times the area). A good set of reflective (white foam-core, or mylar covered) panels nearly negate this.

Quote:

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Originally Posted by Splifted

Light intenstiy = Total Light Emitted / ((4 x pi) x (radius^2))

And light intensity decreases by 1/x^2 where x is the distance.

So like if you have 135,000 lumens at 1 foot, you increase that to 2 ft, you it would be 135,000 x 1/2^2 which is 1/4 so basically one fourth of 135,000 = 33,750. Add one more foot, 135,000 x 1/3^2 = 135,000 x 1/9 = 15,000.

Crazy huh? Thats why the top bud always is so big and the bottom ones are smaller, cause they get a lot less light. LST'ing takes that problem away, preventing you from having like 5 feet from the top to the bottom of the plant.

So thats the science behind bigger buds.

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