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LED grams per watt


Well-Known Member
So... This has been a fun read.. And I'm 2 years waaaaay to late... oh well. If anyone's here.

I have a 300w and 600w viparspectra led with a max combine actual draw of 412w.... am I right in thinking that I should calculate my tramp per watt on the actual draw... I know there or other factors and I'm more likely to get 0.5gpw. But that's the basic calculation right???

My tent is a 2x4


New Member
Wow just read the first couple pages of this thread and I was like "wtf?" until I noticed the date. Times changed pretty quickly!

Yeah you would use draw wattage from the wall because it's a rough measure of efficiency. These days a grower with any experience would have to abuse their plants pretty badly to pull less than 1.2 grams/watt in flower using modern LEDs.


Well-Known Member
GPW doesn't mean anything, it's just a made up KPI by light and seed pushers...
It doesn't say anything about how much electricity you use and you can ''cheat'' by vegging for a long time and do a ScroG grow in a large area with low wattage.

You have to factor in total kWh, time and space to get an idea of efficiency.

+2 GPW can easily yield a lot less in a year than -1 GPW (ScroG vs SoG) same kWh, same grow area ;)

Do you want a high GPW or more weed for the same money, easy choice :D

I use milligram per m2 per day per kWh(from all electrical equipment) to compare stains/phenos, methods, lights etc.



Well-Known Member
Thanks guys. And yh it was a hell if a read and from 2years a go I'm sure leds have moved on in quality.. well hopefully I can aim for a gpw...

I will be vegging longer aswell as Evan though I don't want extreme vegging time. It makes sense to grow with less soil nd nite expense as possible.. few plants scrogged down with 900w of leds I'm laugjunv. Think I'll get 2 red cobs aswell for added power to the flower. Thanks for getting bk to me


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I don't know other brand, but for our Mars lights. Usually our growers get around 1g/w; If they grow experienced, some can do 2g/w; Because it is still a little different to grow under LED compare with HPS, so the final result is also depend on growing experience. The more you grow, and they more you learn, the better you will grow. :circle-of-love:
So, apparently hosebomber, in another thread, gave some definitive
data about this, debunking the 1/3 the power, and thus the 3 grams
per watt. So, the yield we'd be looking for for commercial lights is
1.5 grams per watt.

Is anyone getting that? With whose lights? Note that it's only
with a GOOD light that you'll even get that. LEDs are barely ready
for prime time -- "truth about LEDS" notwithstanding.

- Lenny Gray -

| On 8-18-12, at 10:44 AM,
| Hosebomber wrote:
| Re: LED lumens, again
| To date no other company has shown the proven results as well
| as Advance IMHO. However there are a few good companies on the
| market. If you see a company claiming 1/3rd the power use of
| a HPS or claiming the light is a 900 and actually draws 387
| (true statement about 1 company) close that browser tab and
| move on to the next. If they are lying about their product
| there is a reason.
| [emphasis Lenny's]
| ie with a very good 400 watt led you could get about the
| same yield as a 600 watt HPS. To get better efficiency than
| that it needs to be a custom panel built for your grow area
| and then 40% power reduction is close to max. I've gotten as
| high as 47% power reduction with almost exactly the same yield
| (within 1 gram of tomatoes) in a hydro setup with light barriers
| and running the same nuits to both sides and light being the
| only variable.
I can get 1.5g per watt dried and cured very easily with my hlg 320watt in a 2x4 area.


420 Sponsor
Yes! The white sunlike spectrum light will give you better yield, our TS, SP also, we have a few clients growing the SP 250, 230w from start to finish in the 2x4 tent, one get 416g, another get 435g. :D


Well-Known Member
PGR is correct GPW means absolutely nothing
Wouldn't say nothing. It's a rough estimate of potential yield based on what the light is capable of per X area asuming you've filled the useful footprint of the light.
If you had 2 spaces, both 1sqm.
You perfectly fill a scrogg in both spaces with the same strain.
In space 1 you use 400w for bloom and you should get 400-600g back.
In space 2 you use a 600w and you should get 600-900g back.
1-1.5 gpw.


Well-Known Member
too many variables to be an accurate measure
Not really mate, it's just based on the assumption that you know how to grow and can fill a foot print. There are a lot of variables but they're taken out of the equation by that.

Nobody's gonna base what a light is capable of by taking into consideration that some folk just can't grow very well, live in the Arctic, have cannabalistic cats or think you can grow a pound in a 3L pot.

I've been perpetual (By that I mean random and chaotic lol) for a while now so don't have any recent solid numbers but the first 2 years I had only 2 x 240w blurples. Didn't matter what I done. 1 auto, 6 autos, 1 photo, 4 photos, NFT Res, 10L fabrics, 20L bafrics. I tried everything mate and always got 470-620g.
1-1.3 gpw every time from 10 year old blurples.
Didnt make a difference how many plants I used, how long they vegged for, how much light I used for veg, the numbers were always the same.
Surprisingly enough the best yield was from a single auto too.
The only constant in the grow room was the lights and the fact that I filled the footprint before they hit bloom. Everything else was completely different every time as I was experimenting to find what works best .
If I ever figure it out I'll let you know lol.

Old leds and cheap HPS or CMH should net you a gram per watt.
Top end LEDs , gativa level HPS and the hortilux style CMH lights can all get double that in the right hands.
Not my hands sadly cos I'm a cheapo and still stuck with my stone age tech but I've seen it done enough times in enough methods to know it's about right.

Yes it's asuming your grow goes at least 90% perfect with the other 10% being no more than minor blips and your plants being pretty well trained for optimum light penetration but again, Not the lights fault if any of that isn't upto scratch.


Well-Known Member
and I'm not your mate!
Guessin by the tantrum you cant hit a gram per watt iether then :snowboating:
Was just trying to explain where the companies get these numbers from ehm.... non friendly, agrro person. Its cool though. Not here for an argument at 8am so ill just jog on. Peace out :Namaste:


Well-Known Member
don't presume what I can and cannot do
companies have all manner of nonsense to keep themselves afloat
GPW is at the top of the list
As advertised by one of our most revered lighting sponsors haha


Well-Known Member
don't presume what I can and cannot do
companies have all manner of nonsense to keep themselves afloat
GPW is at the top of the list
As advertised by one of our most revered lighting sponsors haha
So you cant then? Thats the only reason youd be so annoyed by what i said.
Spend top dollar on the qbs and not getting the results i claim should be possible so get all aggro about it.
Just chill and have a smoke man. Its monday yaay :)

Buds Buddy

Grow Journal of the Month: May 2020
GPW is nothing more than a rough estimate of what you can yield if all variables are perfect. The stats also include the variable of those watts being used per square meter. I've never calculated any of my grows to see how many grams per watt I got. I still think the best bud I grew was from the HPS 600 watt. But the electric bill was outrages. Almost 3 - 4 times more than using my LED's. The yield is slightly less; but the difference in the electric cost makes the LED's the more profitable way to go for me.
Here's a couple of pics from my current grow using 2 - 900 watt LED's & 1 - 450 watt LED. There are 4 Auto's in my tent & they pretty much fill the entire 5' x 10' tent. Still have a couple weeks til harvest so unable to post the results yet.
I had to put a SCROG net at the top of my tent to keep the branches off the lights.


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I agree with Stunned. If you grow less plants, and in a short time, you will get less harvest and so less gram/w, if you grow more plants and longer time, maybe you will get better harvest and better gram/w. :circle-of-love: But what really matters is the light spectrum if it is suitable for plants growing, and also the PPFD output can meet the plants' growing needs, :green_heart:
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