How many watts for a small grow 2-3 plants

Hi guys
I'm looking to plant a new seed/cutting every 20 days throughout the year so that I have a consistent supply and somewhat limited space.
Assuming the average lifespan of around 8-10 weeks from seed (dependent on strain), it seems fair to say that I will probably have 2-3 maybe 4 at the most on the go at any given time.
Many people swear by using a large, powerful light such as 400W, 600W sometimes 1000W at quite a distance and this seems to be the norm.

Today I want to propose to you something different.
At least for a small grow like mine, would it be better to use a 100's of watts LED spread over all the plants or maybe a 45W LED grow light for each individual plant? (total of up to 4 lights)

The idea behind this is that I can put a lower wattage light closer to the plant therefore increasing the light intensity (luminous flux or lux) for the individual and therefore increasing yields.
As far as I'm aware, lux meters don't work accurately on red-blue LED grow lights, but you can estimate and use some simple math based on a normal white light.
Currently I have a cheese strain under a 22W white light, just starting week 3 (will be upgrading to higher wattage when the plant is bigger) and the top of the plant is receiving around 64,000 lux about 3 inches from the light. The plant looks completely different each week with minimal stretching.

Typical natural sunlight is usually between 30,000 lux and 120,000 lux. 30,000 lux being like england and 120,000 lux being like maybe a very very bright sunny day for the sahara desert or something.
For vegetative, the maximum lux plants should be exposed to is 70,000 lux. In flowering, 85,000. Anything much higher and you're giving the plants more light than they can use, wasting electricity and potentially harming the plants too, cause that is a thing.

When the wattage of the light doubles, the lux at the same distance doubles.
However when you half the distance, the lux quadruples. Remember plants do not understand watts, only light intensity. I see people talking about watts/sqft all the time yet this does not take into account distance from the light, or how efficient the light is. 40 watts/sqft with something like a cfl or HPS will have a much lower light intensity than the same in LED as more watts are being turned into heat.

What do you guys think?

Start here..http://ledgardener.com/lumens-par-ppf-and-ppfd-measuring-cob-grow-light-output/

14-15 par watts per foot is a good place to be as far as keeping the photon count down without sacrificing a lot of yield. PPFD around 750, but you can still get good results with under 14 par watts per foot. More light is better up to a point so it just depends on space involved and necessary yield.

Plant size varies so best way to inquire is to let us know how many square feet you plan on lighting.

Rahz said:

14-15 par watts per foot is a good place to be as far as keeping the photon count down without sacrificing a lot of yield. PPFD around 750, but you can still get good results with under 14 par watts per foot. More light is better up to a point so it just depends on space involved and necessary yield.

Plant size varies so best way to inquire is to let us know how many square feet you plan on lighting.

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How did you find out what the correct PPFD is? Researching, I can find specific numbers for lux but I am struggling to find information out there for light intensity related to PAR

I made this chart using data from a study. It's based on vegetative growth. The flowering curve has been reported to be more linear but I've used PPFD in the 700s extensively and it has yielded in the 50-60 g/swft range in hydro.

Rahz said:

I made this chart using data from a study. It's based on vegetative growth. The flowering curve has been reported to be more linear but I've used PPFD in the 700s extensively and it has yielded in the 50-60 g/swft range in hydro.

View attachment 4070806

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What can I use to measure this in relation to the distance between a grow light and the top of the plant? Will a PAR meter tell me the PPFD or only the PPF? If only PPF, can PPF be used with some simple math to find PPFD? I'm not a genius so please excuse me if that sounded stupid.
General idea for me is to make sure the light for its wattage is at optimal distance from the plant and in particular not too close so as to light bleach the plant or waste watts on giving the plant more PAR than it can make use of.

Read the link i posted again as it explains all this quite clearly

Fudgepackers said:

What can I use to measure this in relation to the distance between a grow light and the top of the plant? Will a PAR meter tell me the PPFD or only the PPF? If only PPF, can PPF be used with some simple math to find PPFD? I'm not a genius so please excuse me if that sounded stupid.
General idea for me is to make sure the light for its wattage is at optimal distance from the plant and in particular not too close so as to light bleach the plant or waste watts on giving the plant more PAR than it can make use of.

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A par meter will display PPFD at the point of measurement.

I've learned to gauge intensity by just sticking my hand under the light. If the light is too bright my skin starts to look bleached. You can kinda tell by just looking at the brightness of the leaves and tops. It takes a little practice, but if the light is too intense it's not going to hurt the plants unless they're so young they haven't established a root system yet. They will start to bleach a little on the tops, at which point you would move the light up a bit. I used to run a system providing 14 par watts per foot, 30w cob emitters (10-11 par watts each) as close as 4" directly under them without bleaching.

There were several occasions where I let the top buds grow up through the frame of the lamp. The lamp was basically inside the canopy, or right up on it, depending on how you want to look at it. So I wouldn't necessarily recommend purchasing a nice par meter based on what you're wanting to do. Just eyeball it and adjust as necessary.

Rahz said:

A par meter will display PPFD at the point of measurement.

I've learned to gauge intensity by just sticking my hand under the light. If the light is too bright my skin starts to look bleached. You can kinda tell by just looking at the brightness of the leaves and tops. It takes a little practice, but if the light is too intense it's not going to hurt the plants unless they're so young they haven't established a root system yet. They will start to bleach a little on the tops, at which point you would move the light up a bit. I used to run a system providing 14 par watts per foot, 30w cob emitters (10-11 par watts each) as close as 4" directly under them without bleaching.

There were several occasions where I let the top buds grow up through the frame of the lamp. The lamp was basically inside the canopy, or right up on it, depending on how you want to look at it. So I wouldn't necessarily recommend purchasing a nice par meter based on what you're wanting to do. Just eyeball it and adjust as necessary.

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Cheers man, very helpful.
Completely understood what you said about eyeballing it as I do it too. When the light is literally shining off my hand I already know the light intensity is too high.

I wouldn't over think it. KISS??

What light IMHO depends on your grow area, and if its closed up, or not. How large your plants will be. Are you growing Sativa, Indica, Hybrids ? How good is Air Flow, container size ect? All this matters on how much light your plants can use.

If you have a large enough area, and it doesn't get hot, and you have good air flow, IMHO theres NO REASON, NOT to use 1000w. Even 1000w is nowhere near as bright as the sun, and the sun doesn't suffer
Inverse-square law - Wikipedia
https://en.wikipedia.org/wiki/Inverse-square_law

A 1000w Hortilux, at 2 feet above the canopy, in a 4 x 4 area, the FAR edges of the garden, still receive as many lumens vs the sun at the equator, and the Hortilux has the best PAR rating of any 1000w lamp, except the Dual Ended Gavitas, and the like.

Best PAR for the money is the 630w Ceramic Metal Halide, and I'm not talking about the 1 with 2 bulbs. 1 bulb, 600w CMH.., DE

if you have the area, and height ect, Id get a 1000w Hortilux HPS, and run it 24-30 inches above the canopy, and they will reach full potential, in the fastest amount of time.

This is also probably the cheapest route.

I like to use simple 15$ lux meters and conversion factors to get an idea of the ppfd. There is a thread somewhere in the LED section about these factors and how to calculate it for a given spectrum(SPD chart, datasheet).
For an CXB3590/3500°k/CRI80 for example you need to multiply the lux readings with factor 0,014152 to get μmol/s/m² or ppfd. Factor for 3.000°k/CRI80 spectrum is ~0,015.

1000w Horitlux HPS Superbulb is 145,000 lumens, and 1600+umol,. Supplies 60+w Sq/Ft for a 4 x 4 at 36 inches from canopy. With the right temp control, and air movement, I can easily get the bulb 18 inches from the canopy.

DE 1000w Gavita at 38 inches is 166,000 lumens, 2100umol, and good for 5 x 4, but for 100% you cant get them closer than 38 inches. To much Infrared.

Hmm!? Thats theoretical numbers, mate!
What are the real ppfd numbers at 3 foot distance? After reflector and wall loss I would estimate it's far less than 1600μMol/s.
BTW,
He wants to grow only 3-4 plants, one new at intervals of 20 days and in a limited space and he has decided against the use of HPS. If he had wanted information about 1000w hps/630w cmh, he would not have opened his post in the LED area.
I don't mean this to offend in any form, CMH is a realy good light source. But with his conditions I would rather recommend to use multiple 100w CMH's with only 8" height above the canopy.

I grow 1 plant x 1000w in a 20 gallon container, and pull 24oz everytime with a Super Silver Haze I been running 3 years. So for me 1 plant is a pretty big grow, or at lest it can be for the space.

If I veg slightly smaller, train, and bend, use 2 x 20 gallon containers per 1000w Hortilux I get 2lbs+ easy.

The 1000w also allows me to veg several plants in 5 gallon containers, and give them all good space for branching. No Crowding.

All I can tell you about the Umols, and height.

Hortilux recommends their 10000w bulbs be used 30-36 inches from the canopy, and they rate the bulb at 1600umol+, but they also don't believe umols are the best representation ect, but did rate their bulbs at 1600omul+.

So logic dictates the bulb is 1600umol at Hortilux recommendation of 3 feet distance, and if its not, its still PLENTY, and way more than most anything else puts out, especially considering the bulb will totally blast a 4x 4 area, and will also penetrate at least 3 feet.

Also the set up is cheap vs how powerful they are.

Nope, it's not!
Note, the results are for the Digilume DE and it did extremely well. This unit have center par with the highest readings we've ever recorded for an indoor growing light.

Have a look here:
https://growershouse.com/blog/digilume-1000w-double-ended-de-complete-fixture/



You confused PPF and PPFD, mate! 1600μMol/s is the ppf of a bare bulb hanging in a ulbricht sphere.

Notice the Digilume, also has to be at least 38 inches above the plants??? I can get a 1000w Hortilux at least 18 inches. 2x closer. Hortilux doesn't have near the IR vs the DE bulbs.


All the DE fixtures outperform Halide/HPS.

And the Gaviita isn't made to be used in a square.
Its proper footprint is longer vs wide.
I was just using Gavita as an example. All the DE cost more than a normal HPS/Hortilux, and in many cases, unless you have at least 38 inches to use from the top of the canopy, the light on any of the DE 1000w is to strong. To much IR.

My buddy cant use Gavita/DE because he doesn't have the headroom, but he can grow 4 foot tall plants, in 15 inch tall 20 gallon containers with the Hortilux, and get the bulb 20 inches, or closer, to the top of the canopy. How bright is that ??

The Hortilux 1000w has more than enough power to satisfy the pickiest sativa. I don't really care about gwtting into specifics, and over thinking it.

The 1000w Hortilux will blast a 4 x 4, and you don't have to keep the light at least 38 inches from the top of canopy.

Maybe, but the 1600μMol/s is only in the centerpoint meassuring and it still produce a lot of unwanted heat which needs to be removed. With a few Quantumboards (4 or 5) and a 600w driver one could outperforme any available 1000w HPS with only 60% energy needs.(1040w HPS vs. 630w LED)

My best is 21 zips from a 350w output lamp over 10sq/ft using 14 Vero29g5 at 700ma, 25w each.

Currently running 8 CLU058-1825s 50w each in the same space, about halfway through the grow now, it's looking nice and I'm probably going to get somewhat better yield and g/ft, hesitate to say better GPW but lamp efficiency went from 42% to almost 60% so it's possible. I will need to hit 24 zips (and 67 g/sqft) to hit the same GPW. The space is slammed with light. I would have several others running but I have a pythium issue I've been trying to work out.

It's all hydro so not comparable with a soil grow, but still...

Day 26 of 12/12, 3500K 80CRI on the left, 3000K 70CRI on the right:

Rahz said:

My best is 21 zips from a 350w output lamp over 10sq/ft using 14 Vero29g5 at 700ma, 25w each.

Currently running 8 CLU058-1825s 50w each in the same space, about halfway through the grow now, it's looking nice and I'm probably going to get somewhat better yield and g/ft, hesitate to say better GPW but lamp efficiency went from 42% to almost 60% so it's possible. I will need to hit 24 zips (and 67 g/sqft) to hit the same GPW. The space is slammed with light. I would have several others running but I have a pythium issue I've been trying to work out.

It's all hydro so not comparable with a soil grow, but still...

Day 26 of 12/12, 3500K 80CRI on the left, 3000K 70CRI on the right:
View attachment 4071093

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Too bad you couldnt afford the 90cri chips...

thetr33man said:

Too bad you couldnt afford the 90cri chips...

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I have a few V29C Tasty lamps around. Every grow is an opportunity to do a test of some kind so you won't find me working with 90CRI exclusively unless/until the science is settled.