Determine your lights power....

For our purposes, the source is, of course our lights. R is your lights one square foot away from the tops....
Your light is providing this much lumen output area coverage OVER your canopy, and the same penetration down into the canopy.
2R is two square feet away, and represents 1/4 of the lumens reaching your plants
3r is three, or 1/9 th the lumens your plants are getting
4r is 4 sq ft, and it represents 1/16th the power/lumens getting to your plants

So if the light is 4 feet from the medium, you are getting 1/16 th the lumens your lamp puts out to the bottom branches of your plants......


So if your lights are 4 feet from "the medium to tops" those lower branches are only getting 1/16th the lumens.............140000

Lets use a 1000 watt HPS 140,000 "initial" lumens for an example here.

At 1 foot you get the full 140,000 lumens per sq foot. Area and depth of your canopy.......

At 2 feet into the canopy you only get 35,000 lumens

At 3 feet into the canopy you only get 15,555.5~ lumens per sq ft

At 4 feet into the canopy you only get 8,750 lumens per sq ft


Which is pretty dam good.....

So lets take a look at a CFL.....lets pick one....say a 40 watter.....

40 watts @ 18000 lumens.....
R= 18000 lumens
R1 = 4500 lumens
R3 = 2000 lumens
R4 = 1250 lumens


It is just a nice scientific way of saying you need a lot of light to penetrate into the canopy......and the breakdown of just how much light those lower brances get......
Now if you start using "side" lighting........that really ups those lumen out puts

+rep for good information =)

dont forget these numbers are by the Sq ft.

you will still have to divide the total amount of Lumens, by the total amount of Sq ft of your grow area and thats your lumens per square foot.

Big mike....I might have not made myself clear~ thanks for your input....let me try to explain in laymens terms.....we dont need to divide anything.....the Inverse Square Law states... and this is ONLY for ONE LIGHT.......

The intensity of light, from a point source(energy per unit of area perpendicular to the source) is inversely proportional to the square of the distance from the source~ so an object, twice as far away, recieves only 1/4 the energy in/at the same time period....

Click to expand...

Exponentially....it devides it'self!!

i still am not understanding this in growing terms for lighting. just seems misled to me.

this would mean you had one plant in a 1 sq ft area with a 1000hps above it......not going to work.

and i have yet to see a cfl with this many lumens....

"So lets take a look at a CFL.....lets pick one....say a 40 watter.....

40 watts @ 18000 lumens.....
R= 18000 lumens
R1 = 4500 lumens
R3 = 2000 lumens
R4 = 1250 lumens

maybe im just not getting it....


edit: a 70w hps only puts out 8000 lumens

i am away from home for 5 days as of today so i un-plugged everything in my house except the fridge and everyhting in the grow room. 2 8 bulb T-5's and 3 fans. and a 950 gph air pump. my kw hours when i left today were 420,,go figure, i will let you know what the total is on friday.

with the info in your post and the info in this chart, now im really..

BIGMIKE13 said:

with the info in your post and the info in this chart, now im really..

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this chart has nothing to do with a canopy penetration of light. this would be true for the discussion if we were talking about how high a light needed to be mounted for a crop of clones. but i would still want to use the above formula to figure out the penatration lev el of the light you are using for a sog grow or etc.....so you could maximize your yield.

o.k. fine, but the chart states that 1000hps at one foot from the tops is 44563 lumens.
now take that number into your calculations not the 140000 lumens. and pencap i know your trying to help understand this, i would just like to understand better.

and kochab, penetration would not make sense in a sea of green because you are only going for top colas.

there are too many factors to figure penetration imho. (plant per sqft, strain, and thickness of foliage) i would like to figure this out.

i dont know why others havent chimed in.....

all this math really confuses me. so i bought one of these.........

so i have my 400 watt hps 14inches from the plant. so this is a really good distence?

fdd2blk said:

all this math really confuses me. so i bought one of these.........View attachment 45138

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and he uses this for the sun.........

i need to burn one..

bwinn27 said:

so i have my 400 watt hps 14inches from the plant. so this is a really good distence?

Click to expand...

Sorry I confused everyone.....
Bwinn....if you can put the back of your hand at the top of your plant and not feel heat, youre good...


The 1000 watt reference is just that, a reference....we know we would not put a 1000 watt lamp THAT close to a plant, it would fry.........what I am saying here is that at 1 foot away the lamp puts out x lumens, which in this case is 140000 lumens....
at 2 feet away.....the lamps power diminishes......exponentially over distance!
depth and area
High times has an article on it this month~ tried to find a link but it's just not coming up...


but the fromula goes like this


your lumen out put = x

at 1 foot you get x lumens
at 2 feet devide x by 4
at 3 feet devide x by 9
at 4 feet devide x by 16

I was just thinking the same thing. All this math is giving me a headache. light meter. (smart thinking and easier and the head.)

fdd2blk said:

all this math really confuses me. so i bought one of these.........View attachment 45138

Click to expand...

BIGMIKE13 said:

with the info in your post and the info in this chart, now im really..

Click to expand...

This chart is i believe from point to point....not for COVERAGE/area/depth....

C'mon Lacy!! Dont take the easy way! Learn!!! What do those light meters TEACH you?

pencap said:

C'mon Lacy!! Dont take the easy way! Learn!!! What do those light meters TEACH you?

Click to expand...

taught me a lot. you can see it in real time. not just #'s on paper.