What is the point of deminishing returns? Min-Max Watts per sq foot.

[guest 77721]

The grams per watt measurement is a good indicator of personal progress or when comparing similar systems but really falls down when comparing different systems. Not all the lights put out the same intensity and the same spectrum. Comparing grams/Lumens is a better indicator.

HPS
Watts...Lumens....Lumens/Watt
1000....145000....145
750.....110000.....147
600......90000.....150
400......50000.....125
250......29000.....116
150......16000.....107
70........6300........90

CFL
42 .......2700........64
26 ...... 1700 ...... 65

If we use a 600 HPS as the standard for 50 to 65 w/sqft as optimum, it works out as 8000 to 10000 Lumens per Square Foot.

It seems that high powered HPS lights 400-1000 Watts put out similar lumens/watt but it really falls off as you get into the smaller lights. CFL's and Florescent lighting need roughly 125 to 170 w/sqft for 8000 to 10000 Lumens/sqft.

 

[JamieShoes]

it's all relative man... whats the point of 750 grams of something you wouldnt smoke if you could have 350 of something you loved.....

 

[DankHank]

i have grown very dank nuggz under 35,50,70 wpsf.
if you can dial your strain, growroom & skills 30 wpsf is pleanty. its what you grow and what you know

 

[Throwgar]

i have grown very dank nuggz under 35,50,70 wpsf.
if you can dial your strain, growroom & skills 30 wpsf is pleanty. its what you grow and what you know

Show me a nugg from 30 w/sf, and I'll show you something completely different grown with 150 w/sf. Although the difference is mostly quantity.

 

[VerdantGreen]

just a reminder of the definition of 'point of diminishing returns'

the point/level at which each additional unit of variable input (in this case watts/sq foot) yields less and less additional output (grams/watt)

V.

 

[guest 77721]

I've been monitoring my own grows closely and have been growing between 3400 and 8000 Lumens per sqft with CFL's and 150 HPS. I have yet to get over 8000 Lumens/sqft.

My grows are running 7-9 g/1000 Lumens or 1.2-1.3 g/w if I had a 600 HPS. The g/kL is linear and I haven't shown diminishing returns by increasing lighting intensity.

With the CFL lighting, the point of diminishing returns in g/w is about 85 w/sqft.

I'd like to throw my 2 cents into the pot. I'm a hobbyist and a medical grower and there's a difference between Hobbyist and Commercial growing.

When you look at g/Lumens it is a fair appraisal of the grow interms of the light intensity and can be used as a general comparison between growers and technique.

From a commercial point of view, g/watts makes sense as it is a measure of efficiency in terms of power consumption. If this is the yardstick to be used, then this measurement is strongly biased in favour of the 600 HPS which produces 150 Lumens/Watt.

 

[Hydrosun]

I've been monitoring my own grows closely and have been growing between 3400 and 8000 Lumens per sqft with CFL's and 150 HPS. I have yet to get over 8000 Lumens/sqft.

My grows are running 7-9 g/1000 Lumens or 1.2-1.3 g/w if I had a 600 HPS. The g/kL is linear and I haven't shown diminishing returns by increasing lighting intensity.

With the CFL lighting, the point of diminishing returns in g/w is about 85 w/sqft.

I'd like to throw my 2 cents into the pot. I'm a hobbyist and a medical grower and there's a difference between Hobbyist and Commercial growing.

When you look at g/Lumens it is a fair appraisal of the grow interms of the light intensity and can be used as a general comparison between growers and technique.

From a commercial point of view, g/watts makes sense as it is a measure of efficiency in terms of power consumption. If this is the yardstick to be used, then this measurement is strongly biased in favour of the 600 HPS which produces 150 Lumens/Watt.

How are you doing on grams per square foot per flower day? I am using two 50 square foot sections under 2KW each and am trying to improve this figure. Right now .5g per square foot per flower day is my production level.

Peace,

 

[guest 77721]

With my cab at 5400 Lumens/sqft of CFL's, I'm running 0.6 g/sqft/day with a 9 week LUI, 10 week Shiskaberry and a 11 week Thai-Lights. All the results are close over 2 back to back grows.

The best I've grown is Shiskaberry 0.9 g/sqft/day with a 150 HPS @ 75w/sqft, 8000 Lumens/sqft.

Here's a table of common bulb wattage sizes and their Lumens output.

​

If we accept that a 600 HPS @ 55 to 65 w/sqft is the optimum, then 8,000 to 10,000 Lumens/sqft is the optimum light intensity.

The Lumens per Watt falls off terribly with the smaller lights. If you have a large grow room it makes sense to add more growspace than to add another light. With the small cabs it makes sense to setup for 8000 to 10,000 L/sqft even though the g/w falls off between 75 and 85 w/sqft.

Incidentally, to make g/w a fair assessment between lights, multiply your g/w by the W/L multiplier which is normalizing it to the output of a 600 HPS light.

 

[British_Bulldog]

I know this debate is a bit old now, but I just read it.

What I noticed no-one said was it's all relative on the actual plants, and how much light They need.

e.g. Aeric 77 Cali-O would thrive under 30W/sq.ft., but a light-loving Haze would easily accommodate 80-100W/sq.ft.


Peace

 

[Hydrosun]

Show me a nugg from 30 w/sf, and I'll show you something completely different grown with 150 w/sf. Although the difference is mostly quantity.

There is NO way the size or quality of this smokes increases by much (40w per sqft), even if you did want to put 350% more light on it.

Peace,

 

[jomby]

Comparing grams/Lumens is a better indicator.

Hey there, I'm new here, but I would like to inject some of my factual knowledge on the matter of lighting measurement:

The SI unit the Lumen is a measure of an "average" value of intensity over an area of space, multiplied by the sensitivity of the human eye (the photopic spectrum). In math terms this is expressed as the relative luminous flux (lumens) equals the closed integral over an area of space (generally a sphere, as it is easy to calculate) of the luminous intensity on that sphere, multiplied by the photopic curve. This gives you a "weighted average" of the perceptible power being emitted by whatever is inside the sphere, i.e. a lightbulb. It is useful when comparing lightbulbs for human use, however, as we're all well aware, the sensitivity spectrum of a plant is basically the inverse of that of the human eye, with green being the least sensitive color and red and blue being the most sensitive. This means that the lumen is a completely wasted dimension when comparing lightbulbs for plant usage.

Now, one could conceive of a "plant lumen" which used any of the spectra associated with plant growth (although there are many and each plant is different) however this has not been given much thought in the scientific community.

The unit that should really be used is Luminance, or Candela/m^2 which is basically a Lumen without the photopic spectrum multiplied in. Unfortunately, bulb manufacturers do not provide this information as standard. If you were able to procure the color spectrum of a bulb in question, and the lumen value of it, you could back-calculate the luminance value from those two pieces of data. This would give you a much more useful value for comparing horticultural bulbs.



Edit: on second thought, anything with the prefix "lumi-" has the photopic spectrum factored in. Radiant flux is the term I meant to use, and this can be derived from a lightbulb's color spectrum and luminous flux by dividing out the photopic spectrum. This would make significant changes to the power rating of MH vs. HPS vs. Fl bulbs.

 

[Iron_Lion]

I posted this in another thread but thought I should post it here too. I current have 2 250 watt grows going on, one cab with 100 watts per sq foot, 1 with 50 watts per sq ft. I have the same strains mixed between the 3 boxes, i notice no noticable difference in bud size between the 2 boxes. In fact some of my largest plants are in the tent with 50 w per sq ft.

My mid grow prediction is that the tent with 50wpsf is going to yeild way better than the box with 100wpsf. Reason being, there is way more surface area, allowing for more bud sites per sq ft/more plants under the light. I have 4 plants in the cab, 7 in the tent, all in 3 gal bags. having the proper footprint also allows me to maximize the amount of soil I use, which hopefully also translates into more buds. This is far from a scientific test, but an observation none the less. This will be the last time I use to 100wpsf cab, it has served me well over the last few years but now is the time I learn to run my grows most efficiently, my 600 watt closet will also be 50 watts psf.