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how many lumens to grow weed

How Many Lumens Do I Need for My House Plants?

Greetings to you, Nico!
I have searched the web and noticed that you are the guy to ask about indoor lighting for cannabis horticulture. My question is rather simple, I think: In terms of lumens, what light output do I need to grow a plant or two successfully in my home? I have a small bedroom and am thinking of using a ’ x 4’ or 4’ x 8’ grow tent? Any suggestions on bulb types and strength would be helpful! Many thanks & good luck to you! — Jonathan V. via the mailbag at [email protected]

Thank you, Jonathan, for reading and writing in with an excellent question!

Deciding on light setups for any indoor garden can be a daunting task. The horticultural lighting industry almost feels like it is purposefully trying to confuse us sometimes, possibly in the hopes of getting consumers to purchase more items—or more expensive items—than we really need.

A good example of this is the fact that many bulbs are still marketed using “lumens” as a selling point. While lumens are a measurement of light quantity, it is not an appropriate term for horticultural purposes.

Lumens would be used to describe the strength of light if you were trying to light a stage or illuminate an object for viewing purposes. However, for photosynthetic purposes, the proper quantification of light uses PAR values, which stands for “photosynthetically active radiation.” This measurement of light provides information on both the quantity and quality of light being emitted by a source in relation to its effectiveness and efficiency for the plant’s photosynthetic processes. It takes into account not only strength, measured by photon count, but also spectrum, measured by color or wavelengths.

However, rather than go too deep into PAR, I will answer your question in the more basic form, as lumens do have a place in this discussion, since you specifically ask about lighting a specific size of space. Using a 4’ x 4’ grow tent as the example of the space we want to light, we must first understand how much light is optimal for plant growth and development. To do this, we examine the process of photosynthesis, where light energy (photons) is converted to plant energy (glucose or sugar).

Most plant leaves do their best conversion with sunlight between 3,000 and 4,000 lumens per square foot. Let’s assume, on average, that a 1,000-watt high-pressure sodium (HPS) bulb has an output of 100,000 lumens. At a leaf’s peak efficiency of 4,000 lumens per square foot, that leaves an optimal coverage area of 25 square feet—or a 5’ x 5’ footprint—for a 1,000-watt bulb.

Of course, bulb manufacturers and garden shop sales people will tell you a 1,000-watt bulb covers anywhere from 6’ x 6’ t0 8’ x 8’, but that is not based on photosynthetic processes but rather on physical light coverage (hence the use of lumens and not PAR).

Still, even with a more scientific view, it appears that a 1,000-watt HPS would be plenty sufficient to light a 4’ x4’ tent—or just 16 square feet. However, there is still another factor often not considered when choosing the correct lamp: heat byproduct.

A 1,000-watt bulb produces a staggering amount of heat for a garden, especially a small garden space like a tent. In fact, when you break down photosynthesis even further and analyze the process, we find that photosynthesis has ideal temperatures as well. To be exact, 68°F to 74°F is the “gold zone” when it comes to photosynthesis. At 84°F and above, plant photosynthesis begins to slow down significantly.

In a smaller home grow tent, the best light solution is a 400-watt HPS set-up. (Photo by Nico Escondido)

So while a 1,000-watt bulb may seem plenty sufficient for a 4’ x 4’, it will be too much light. In a 4’ x 4’ x 8’ tent with no exhaust, a 1,000-watt bulb has the power to raise the temperature nearly 25 degrees in no time. That means 68°F can climb to over 90°F! Even with ample exhaust, you’d be hard pressed to keep temps below 80°F.

The solution is simple: a 400-watt or 600-watt will serve you and your plants much better. A 400-watt HPS puts out approximately 50,000 lumens. With a 16-square foot footprint in a 4’ x 4’, that’s 3,125 lumens per sq. foot. A 600-watter is roughly 80,000 lumens, giving 5,000 lumens per sq. foot in the same tent.

So the smarter choice in a 4’ x 4’ is going to be the 400-watt HPS due mostly to the heat factor, which should never be underestimated. That said, if you’re cramming more than four plants in a 4’ x 4’—and you plan to have excellent exhaust and maybe even some cooler air being pulled into the tent—then you could consider the 600, but it would be risky. If you don’t mitigate the heat properly, the 600 might cost you more in quality than you would gain over the 400 in yield.

LEDs could pose an alternative in the future, but right now, LED companies like this one are going belly-up after coming to market with a $1,400 price tag. (Photo by Nico Escondido)

Thanks for reading everyone and remember: Grow… And help the world grow, too!

Follow Nico on Social Media: @Nico_Escondido (Twitter) & @Nico_High_Times (Instagram)

Thank you, Jonathan, for reading and writing in with an excellent question!

How many lumens does the plant need?

fml456
Active Member
herballuvmonkey
Well-Known Member
Meethrip
Member
Member

your plant doesnt cover an area of 9 feet does it?

i believe you need around 7500 lumens per square foot

Meethrip
Member

hmm. I think I may have mis-interpreted what herball was saying or he may have wrote it wrong.

I cannot quite understand how he has put this.

TheSeawulf
Member

hmm. I think I may have mis-interpreted what herball was saying or he may have wrote it wrong.

I cannot quite understand how he has put this.

Meethrip
Member
figtree
Active Member
samljer
Active Member

Probably because of wrong spectrum.

CFL can bud weed and grow it at a good pace just fine. IF you have the right spectrum.
Dont try buddin in blue (6500k)
wont happen.

samljer
Active Member

I have a space about 1 food deep by 2feet wide.

I have 3 bulbs in there CFL
2700+1700+1700 lumens = 6100 lumen

And people tend to say 2500+ per foot to veg and 3000 to bud *(3500 for denser) is fine.

and you know what, it is.
eventually im going to get 3 bulbs all going at 2700, but they last 10000 hours ;P
and ive done 3 plants at a time with no issues.
So ill give you the advice ive been given by experianced CFL growers and not guys who use HID and say CFL wont bud.

CFL will bud your weed fine at 3000 lumers per each food squared of area.
During budding keep them 3″ near plant tops and they will penetrate fine.

now before all you HID junkies come at me,

Remember, it’s not a contest: We all love the same plant, and there’s hundreds of ways to grow her right. Arrogant growers love to put down other people’s nugs and argue for days about why nobody can produce better pot than they can. These types actually end up infusing some of that negative and competitive energy into their plants. – Unknown Author (High times)

Pacific
Member
Infomad
Member
offworldvacations
Active Member

veg phase: 12 hours on 5.5 off, 1 on 5.5 off (that’s 24 hours). this cycle will not harm your plants and will perform better and reduce about 40% of your energy consumption and you will not have the issues that 24/24 gives you.

flower phase: when you switch to flower go 11 hours and then every two weeks reduce the light by 30mins and when you get to about 9.5 hours just let the kids finish up that way. (this mimics nature and performs better). if your plants won’t finish budding. whatever cycle your using, drop the hours and the plant will do better and finish up.

plants do not perform better under 24 hours of light. let them rest, there are things going on in the dark that are necessary.

and use. induction or led or plasma in combo with uvb bulb. plasma doesn’t cut it without help, wihich is why you should use induction / efdl lighting.

Tyronebiggems74
New Member

I have a space about 1 food deep by 2feet wide.

I have 3 bulbs in there CFL
2700+1700+1700 lumens = 6100 lumen

And people tend to say 2500+ per foot to veg and 3000 to bud *(3500 for denser) is fine.

and you know what, it is.
eventually im going to get 3 bulbs all going at 2700, but they last 10000 hours ;P
and ive done 3 plants at a time with no issues.
So ill give you the advice ive been given by experianced CFL growers and not guys who use HID and say CFL wont bud.

CFL will bud your weed fine at 3000 lumers per each food squared of area.
During budding keep them 3″ near plant tops and they will penetrate fine.

now before all you HID junkies come at me,

Remember, it’s not a contest: We all love the same plant, and there’s hundreds of ways to grow her right. Arrogant growers love to put down other people’s nugs and argue for days about why nobody can produce better pot than they can. These types actually end up infusing some of that negative and competitive energy into their plants. – Unknown Author (High times)

I have a space about 1 food deep by 2feet wide.

I have 3 bulbs in there CFL
2700+1700+1700 lumens = 6100 lumen

And people tend to say 2500+ per foot to veg and 3000 to bud *(3500 for denser) is fine.

and you know what, it is.
eventually im going to get 3 bulbs all going at 2700, but they last 10000 hours ;P
and ive done 3 plants at a time with no issues.
So ill give you the advice ive been given by experianced CFL growers and not guys who use HID and say CFL wont bud.

CFL will bud your weed fine at 3000 lumers per each food squared of area.
During budding keep them 3″ near plant tops and they will penetrate fine.

now before all you HID junkies come at me,

Remember, it’s not a contest: We all love the same plant, and there’s hundreds of ways to grow her right. Arrogant growers love to put down other people’s nugs and argue for days about why nobody can produce better pot than they can. These types actually end up infusing some of that negative and competitive energy into their plants. – Unknown Author (High times)

I currently have 5 plants just sprouting up.. around how many lumens do you think i need..i think i'm running at about 10,000 lumens with cfls..what do you…