# What Wattage HPS ? Light Penetration Explained via Inverse Square Law



## Flo Grow (Mar 14, 2011)

*What's up !?*

*Are you tired of SO much popcorn buds during your harvest ?*
*Are you wondering what light you should get because heat may not be or is not an issue for your grow space ?*
*People ask or want to ask about lumens, and how much light will penetrate their canopy once they learn they can grow 3 feet or taller plants.*
*Some ask because they want nice 2 foot plants with little to no popcorn buds on the bottom of the plant.*
*So really, unless your grow style is something like SCROG or LST where your colas are mainly getting light and aren't more than 12" - 18" tall, then this info pertains to you.*
*I mentioned SCROG and LST because some ppl have height restrictions and these 2 Advanced Grow techniques allow those very same ppl to achieve DRY yields equal to and often greater than those ppl who grow "trees".*


*It's time to learn the Inverse Square Law about lumens and light penetration depth.*

*1 foot from light source = 100% illumination and LUMENS*
*2 feet from light source = 1/4 as bright*
*3 feet from light source = 1/9 as bright*
*4 feet from light source = 1/16 as bright*

*The Inverse Square Law ( ISL ), basically states that your plant will receive 100% lumens IF it's within 1 foot of the light source.*
*For every ADDITIONAL 1 foot of distance AWAY from the light source, lumens and therefore canopy penetration diminishes GREATLY !!!*

*Please keep in mind that those utilizing a glass lens in an air-cooled hood/tube of ANY kind are NOT getting 100% lumens because of the glass lens.*

*For the purpose of simple division, we'll use a light with an output of 100,000 lumens, which is roughly 10,000 MORE lumens that the average 600w HPS and roughly 40,000 lumens LESS than the average 1,000w HPS.*

*1 foot within light = 100,000 lumes (100%)*
*1 - 2 feet from light = 25,000 lumens (250w HPS roughly within 1 foot)*
*2 - 3 feet from light = 11,111 lumens (125W CFL roughly but less than 150w HPS within 1 foot)*
*3 - 4 feet from light = 6,250 lumens (250w HPS @ 1- 2 feet from light)*

*So as you can see, the drop in lumens and how much light penetrates your gardens canopy drops significantly with every 1 foot of distance away from the light source.*
*At 2 feet away, my 400w Hortilux (55,000 lumens) pretty much hits like a 150w HPS, and anything below that gets trimmed off (popcorn buds).*
*Being that my tent is 5 feet tall and my max plant height is 2.5 feet, that worked out to be the best light for me AFTER I bought and used a 250w Hortilux due to not understanding light penetration.*

*Any questions, please ask !*
*Good vibes to you all and your grows !!*


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## suTraGrow (Mar 14, 2011)

Hmm so vertical growing would be ideal then for full lumens usage for the plants. I just set up 3 600watt HPS vertically that i use to use for a SOG (sea of green)set up due to a article i read which is very similar to this. Running vertical just made more sense to me.


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## Flo Grow (Mar 14, 2011)

*To be honest, "ideal" is really what works for you, the individual.*
*It doesn't matter if the plant is grown vertically, diagonally, sideways or inverted.*
*It still needs optimal light penetration for growth.*
*Leaves can yellow and fall off if they're not "earning their keep" with the photosynthesis process.*
*Which is caused by a lack of efficient lighting, but is often confused with nutrient deficiency.*


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## Flo Grow (Apr 4, 2011)

*Forgot about this thread for a second ! lol
Can't make it fit in my damn sig !

BUMP....................
*


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## faithfulmastiff (Apr 4, 2011)

ok i got a question.....

those utilizing a glass lens in an air-cooled hood/tube of ANY kind are NOT getting 100% lumens because of the glass lens... 

ok, so how much do you get with a lens, how much does it take away ?


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## Flo Grow (Apr 5, 2011)

*Exactly big bro.
The lens causes some lumens to be lost.
How much also depends on the inner lining of your hood and it's overall shape as far as length, width and depth.
Half the lumens bounce up 1st, THEN down onto your plants after passing thru the glass lens.
I'm sure the thickness of the lens plays a small part as well.
*


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## 4 the love of ganja (Apr 6, 2011)

so say a 600 watt producing 90,000 lumens in a cooltube 1ft away how much lumens would it really produce


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## Flo Grow (Apr 6, 2011)

*Cool tubes are the worst bcuz of the curve of the lens.
It causes the light to bend more before exiting.
I stared with one too, then bought a real hood.
No offense.

BUT, hypothetically :
90,000 up to 1ft away
22,500 at 2ft away
5,625 at 3ft away
And I wouldn't go beyond that.
So trim everything off the bottom of the plant that's more than 3ft FROM THE BULB, NOT THE LENS.


*


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## faithfulmastiff (Apr 9, 2011)

Flo Grow said:


> *Cool tubes are the worst bcuz of the curve of the lens.
> It causes the light to bend more before exiting.
> I stared with one too, then bought a real hood.
> No offense.
> *




hmmm i was looking at cooltubes too, ok looks like a proper hood it is then


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## faithfulmastiff (Apr 13, 2011)

oooo i like this flange system


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## Flo Grow (Apr 13, 2011)

*IT'S ABOUT FUCKING TIME A MANUFACTURER USED THEIR HEADS TO HELP US THAT ARE IN TIGHT QUARTERS !!!
If this was avail when I copped my hood, it would have been so on !
That should work real good to air cool with the lens on.
*


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## faithfulmastiff (Apr 13, 2011)

Flo Grow said:


> *IT'S ABOUT FUCKING TIME A MANUFACTURER USED THEIR HEADS TO HELP US THAT ARE IN TIGHT QUARTERS !!!*
> *If this was avail when I copped my hood, it would have been so on !*
> *That should work real good to air cool with the lens on.*


 
trouble is that option only available on their $260 xxxl version, i been searching everywhere for just that flange part, can't find it......


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## Flo Grow (Apr 13, 2011)

*This is to help those that want to have a ballpark figure in mind for bulb height above the canopy and the lumens received by the plant(s).

** = for EVERY inch you lower or raise your light you will lose or gain the lumens listed


1K HPS @ 140,000 lumens:

140,000 up to 1ft
35,000 up to 2ft
8,750 up to 3ft ** AND per inch


600w HPS @ 90,000 lumens:

90,000 up to 1ft
22,500 up to 2ft
5,625 up to 3ft ** AND per inch


400w HPS @ 58,000 lumens

58,000 up to 1ft
14,500 up to 2ft
3,625 up to 3ft **AND per inch


250w HPS @ 30,000 lumens

30,000 up to 1ft
7,500 up to 2ft
1,875 up to 3ft **AND per inch


Now this IS NOT to say, if you move said light beyond 3ft that you can no longer grow with said light !!!

Just expect some thin-branched, spiney plants with internode spacing stretched out more than a 10yr Veteran Hooker's Vagina !!! lmao 



Cool Waters
No Lights
*


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## Flo Grow (Apr 13, 2011)

faithfulmastiff said:


> trouble is that option only available on their $260 xxxl version, i been searching everywhere for just that flange part, can't find it......


*So you mean it ONLY comes with the purchase of the hood !?!
THAT is some bullshit !
Although HTG are pretty solid folk, you may have to call them and see what you can arrange.

*


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## matatan (Apr 13, 2011)

u should also cover what 250, 400, 600, and 1000 watt hps/mh cover. for example 400w cover 4'x4' space. i think... lol please confirm or correct and add! great thread +rep!


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## Flo Grow (Apr 18, 2011)

matatan said:


> u should also cover what 250, 400, 600, and 1000 watt hps/mh cover. for example 400w cover 4'x4' space. i think... lol please confirm or correct and add! great thread +rep!



*150w/175W - up to 2ft x 2ft (4sq ft)

250w - up to 3ft x 3ft (9sq ft)

400w - up to 4ft x 4ft (16sq ft)

600w - up to 5ft x 5ft (25sq ft)

1000w - up to 6ft x 6ft (36sq ft)

All these are approximate and can be stretched a little further, but the above areas are generally observed as "more ideal".
*


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## tjsap24 (Apr 20, 2011)

I have a 2' deep, 4' wide, and 6.5 tall cabinet with a 250 hps. Everything works great but im thinking about a 600hps. Is that just total overkill? Would it be worth the extra power and heat or should I just shoot for the 400hps. Just looking for opinions thanks


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## Brick Top (Apr 20, 2011)

matatan said:


> u should also cover what 250, 400, 600, and 1000 watt hps/mh cover. for example 400w cover 4'x4' space. i think... lol please confirm or correct and add! great thread +rep!



If it is has not already been stated, that would greatly depend on the reflector hood chosen/used. Different sizes and different shapes will equate to different sized and different shaped light footprints.


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## Flo Grow (Apr 20, 2011)

tjsap24 said:


> I have a 2' deep, 4' wide, and 6.5 tall cabinet with a 250 hps. Everything works great but im thinking about a 600hps. Is that just total overkill? Would it be worth the extra power and heat or should I just shoot for the 400hps. Just looking for opinions thanks


*You can do either, depending on how well your intake and extraction is set up.*


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## Flo Grow (Apr 20, 2011)

Brick Top said:


> If it is has not already been stated, that would greatly depend on the reflector hood chosen/used. Different sizes and different shapes will equate to different sized and different shaped light footprints.


*True, but still, the particular HPS is still governed by the Inverse Square Law which is about the depth of light penetration.
Different shaped hoods are mainly for the footprint/covered area to be lit, but not so much depth of penetration.
A certain light can only shine so deep.
A particular hood, if able to cast light over a larger area is giving off less light and lumens around the edges really.
*


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## DocGreenThumb (May 1, 2011)

Flo Grow said:


> *True, but still, the particular HPS is still governed by the Inverse Square Law which is about the depth of light penetration.
> Different shaped hoods are mainly for the footprint/covered area to be lit, but not so much depth of penetration.
> A certain light can only shine so deep.
> A particular hood, if able to cast light over a larger area is giving off less light and lumens around the edges really.
> *


Very informative thread Flo. What size reflector would be good to light my 4.6' x 5.7' with a 600 HPS?

I want the largest foot print with minimal lumen loss for light to travel across the hood also it will be an air cooled hood to keep the light as low as possible.


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## farmboss (May 1, 2011)

your rational is no more 'scientific' than saying if you only had 1 gallon a day to water plants, you'd have less water per plant with 20 plants versus 2.

try growing a single plant 1 foot from a 600 watt hps without a glass lens.


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## DocGreenThumb (May 1, 2011)

IDK about that, my light is 8-10" away with the glass lens and a 434cfm about 1/2 strength pulling air through the hood and a 35lb carbon filter. I just cleaned the lens and bulb and it is so much brighter. I'm a lazy stoner and need to get on my cleaning better in the garden.

*You must spread some Reputation around before giving it to Flo Grow again.*


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## Jason2011 (May 1, 2011)

have you tried your local sheet metal workshop?
just go in and tell them what you want. im in australia and got 4 made up for 12.50 each
i also believe you might have some luck in a shop that does fire places, i think flue sizes are similar to fan dia. but might cost more i think they made from stainless steel, mine are made of light guage zincalume


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## spartan (May 7, 2011)

jason, Please tell us more, pics? Where in Aus?


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## Flo Grow (Jun 21, 2011)

farmboss said:


> your rational is no more 'scientific' than saying if you only had 1 gallon a day to water plants, you'd have less water per plant with 20 plants versus 2.
> 
> try growing a single plant 1 foot from a 600 watt hps without a glass lens.


*Sorry I don't drop in the way I should since I started this thread !
For future ref, pm me if i take to long to respond.

Now, I have that in many grows, IN PERSON.
If you can't get your 600w that close, you have other environmental problems to solve.
EVERYTHING must be in order for it ALL to come together just right !!!!!!! *


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