watts per sq. ft. and lumens

Clint Torres

Clint Torres

New Member
:confused:

i have tried to do the search before asking this.

What is the ideal range for watts and lumens per sq. ft. ? I did a rough calculation and i am at about 55 watts / sq.ft. Is that within a good range?

What are the equations to determine your watts or lumens per sq. ft.

I have a 400 watt HPS running on '10% boost" for 440 watts. The light is about 18" to 24" above canopy and 3 to 3 1/2 feet from the surface where the containers sit.

My space is in a small bathroom but my actual size of my grow space is 4' L x 2' W x 4' H.

Can someone tell me these equations or link me to a chart?
Thank you.
kiss-ass
 
Phaeton

Phaeton

Active Member
Depends how far off the lights are.Indica canopy.JPG

I have 130 watts per square foot but my lights are all at least 2' away.
 
darkdestruction420

darkdestruction420

Well-Known Member
ive got a h.o.(high output) hps bulb that puts out 55,000 lumens instead of the normal 50,000 lumens.) Assuming yours is the same as that it would be 55,000 lumens divided by 8 sq feet which= 6875 lumens a sq ft. Ive always tried to go with at least 10,000 per sq ft. 440w divided by 8 ft=55w per sq ft, to be honest i dont really consider watt per sq ft to be of much importance, watts are just how much energy the light source uses.
 
jawbrodt

jawbrodt

Well-Known Member
Ya wanna know 'for sure', what sort of intensity your plants are getting? Go somewhere like Ebay, buy a cheap light meter, for around $30, and take some measurements around your plants. Not only will you know what your plants are receiving, you can also use the meter to adjust your lights, to get max intensity, yet still having good coverage. It's a good tool to have, especially until you know your lights a little better. I set mine up so that the outermost edges are getting at least 3000 LSF(lumens per square foot, actual intensity), and it works out to where the very closest plants, in the center, are getting 8,000+ LSF. That was with a 600 HPS, and i just moved up to a 1000. I'll be happy I have my meter, when it comes time to set that up. No, it's not a necessity, but it sure is nice to 'know'.....
 
sso

sso

Well-Known Member
going above 10 000 lumens psf gives you bit more growth, but not near enough to offset the extra heat you need to deal with.

i.e you get bit more growth.

though, i dont really find going over 7000 That beneficial, specially if im losing footprint because of it. maybe with co2 and a closed system. (probably lol)

rather have 4x4 at 7000 than 3x3 at 10 000
 
sso

sso

Well-Known Member
plus, with more intense light, you lose some of the aroma and potency (more aroma)

though if you can keep the temps 75f above the canopy then its not as pronounced. (its not hugely pronounced, ive got a pretty good nose so no idea how its for you(unfortunetly about as keen as a pregnant woman...(well, its sometimes very unfortunate lol))
 
Clint Torres

Clint Torres

New Member
darkdestruction420 said:
ive got a h.o.(high output) hps bulb that puts out 55,000 lumens instead of the normal 50,000 lumens.) Assuming yours is the same as that it would be 55,000 lumens divided by 8 sq feet which= 6875 lumens a sq ft. Ive always tried to go with at least 10,000 per sq ft. 440w divided by 8 ft=55w per sq ft, to be honest i dont really consider watt per sq ft to be of much importance, watts are just how much energy the light source uses.
Click to expand...
with the fans it's more like 2.5' by 2' maybe 3x2 so i'm actuall getting about 11000 focused in
 
zvuv

zvuv

Active Member
Usually people take the wattage of the light and divide it by the appropriate canopy area. Eg, a 400W light covers a 3'x3' canopy giving about 50W per sq ft. Outside this 3x3 area, the light is below that level. 50W per sq ft is considered about right.

Actually it's a meaningless number. The bulb is rated 400W but that's it's power consumption not it's output. Less than 90% of that 400W actually becomes light. Even with a reflector, the 3x3 canopy area only recieves a fraction of the total output of the lamp. So in fact that '50W per sq ft' is more like 25W per sq ft at the canopy.
 
Clint Torres

Clint Torres

New Member
zvuv said:
Usually people take the wattage of the light and divide it by the appropriate canopy area. Eg, a 400W light covers a 3'x3' canopy giving about 50W per sq ft. Outside this 3x3 area, the light is below that level. 50W per sq ft is considered about right.

Actually it's a meaningless number. The bulb is rated 400W but that's it's power consumption not it's output. Less than 90% of that 400W actually becomes light. Even with a reflector, the 3x3 canopy area only recieves a fraction of the total output of the lamp. So in fact that '50W per sq ft' is more like 25W per sq ft at the canopy.
Click to expand...
I'm not being sarcastic, but does that suck?
I have my 400 on a 10% boost if that means any good increase.

Can you exlain lumens and what lumens/sqft are good and what are "foot candles" I've read about them but it was longwinded. Any tips on those?
 
zvuv

zvuv

Active Member
Here is a post I wrote explaining watts & lumens etc.
Lumens & candles are special measurements that have to do with the way the human eye sees light. They are almost useless for assessing the value of a lamp for growing.

You are in good shape with your 400W lamp and your 4'x2' footprint. 3'x3' would be ideal but what you have is good! You should be able to get 6-8 oz easily from that setup and a lot more with some practice.

Calculating the actual light impinging on the canopy is not a trivial calculation. Only about 1/3rd of the light goes directly from the bulb to the canopy. How much of the other 2/3rds is captured by the reflector and how much is actually reflected back to the plants depends a lot on the details of your particular equipment. So it's not clear it would be worth doing the calculation at all.

As someone who has 22 years experience in measuring light intensity, I can tell you that many people here dont really understand about watts/lumens , the inverse sq law etc. It doesn't matter. They are here to grow. There are a number of rules of thumb that work well enough and that's what we use.

One thing that everybody does seem to understand is how the inverse sq law affects light intensity, and that's very important. Doubling the distance from the canopy to the bulb will reduce the intensity by a factor of 4! This means that a small increase in distance from the light can cause a significant attentuation of the light on that region. It also means that there will be a significant difference between the light impinging on the top of the plant and the bottom. This is why canopy management can make a very big difference in a closet grow. This is why people grow SCROGS

Again, the inv sq Law only applies to point sources. An HID lamp is not a point source but the effect is similar enough that we can use the inv sq law to understand how distance affects light intensity.

So, in sum. Your lamp is well matched to your grow space.
 
Clint Torres

Clint Torres

New Member
zvuv said:
Here is a post I wrote explaining watts & lumens etc.
Lumens & candles are special measurements that have to do with the way the human eye sees light. They are almost useless for assessing the value of a lamp for growing.

You are in good shape with your 400W lamp and your 4'x2' footprint. 3'x3' would be ideal but what you have is good! You should be able to get 6-8 oz easily from that setup and a lot more with some practice.

Calculating the actual light impinging on the canopy is not a trivial calculation. Only about 1/3rd of the light goes directly from the bulb to the canopy. How much of the other 2/3rds is captured by the reflector and how much is actually reflected back to the plants depends a lot on the details of your particular equipment. So it's not clear it would be worth doing the calculation at all.

As someone who has 22 years experience in measuring light intensity, I can tell you that many people here dont really understand about watts/lumens , the inverse sq law etc. It doesn't matter. They are here to grow. There are a number of rules of thumb that work well enough and that's what we use.

One thing that everybody does seem to understand is how the inverse sq law affects light intensity, and that's very important. Doubling the distance from the canopy to the bulb will reduce the intensity by a factor of 4! This means that a small increase in distance from the light can cause a significant attentuation of the light on that region. It also means that there will be a significant difference between the light impinging on the top of the plant and the bottom. This is why canopy management can make a very big difference in a closet grow. This is why people grow SCROGS

Again, the inv sq Law only applies to point sources. An HID lamp is not a point source but the effect is similar enough that we can use the inv sq law to understand how distance affects light intensity.

So, in sum. Your lamp is well matched to your grow space.
Click to expand...
This is some good info. I could get 6-8 oz. ?!?! I guess I need some more of that practice stuff you were talking about. Tell me this, how far above the canopy should a 400 watt HPS be? I do not like the "hand" test, I'd rather have them a bit higher than that.

You mentioning that my footprint/lamp combo is well suited just puts so much oxygen back in my lungs and heaves the weight off my shoulders. I knew for sure that i was making some mistakes at first.

1st run i EVER did I used a shitty 4' 40 watt shop fixture and 3 "clamp on" cfls w/ reflectors. I used MG soil in milk cartons so the roots were exposed to light. I watered w/ tap water that rates a pH of about 8.4 in this area. I not only had light leakage some but also did not have a timer and slept thru turning on/off the lights a couple of times. I grew it from some "mexi-schwag-bag" and was blown away. It was ROCK hard and smelled like a citrus grove, strong. (see pics called, "OOPS" below). the other pics are the ones that are 4 weeks except for the small clones under the T5s.

So I went ahead and got some good seeds from attitude and have run 4 crops, none of which made more than 1/4-1/2 oz. per plant. Of course the more i go the MORE I learn and on this run (all clones I made) everything is happening according to the averages i have read. 4th week flower and there is very evident sugar on all plants' forming buds and little leaves. Right now all the buds at 4 weeks are as big and bigger than finished buds from my "botched" runs. i see definite improvement on this run.
 

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Dizzle Frost

Dizzle Frost

Well-Known Member
If i go by my lamp output i have 22622 lumens / sq-ft ... but i dont get that because my plants arnt directly under the lamp.....depends how high it is from the canopy ....i will always have the same amount of watts / sq-ft tho. But lumens is what matters
 
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