# 50w per square foot?



## grodude (Jun 17, 2015)

I often read that when choosing lighting for a grow room one should aim for a minimum of 50w per square foot. I was curious what the impact is if more or less light is used. If, for example, 40w per square foot is used will the plants grow too slow making it a waste of electricity, or will it simply not reach all parts of the plant. What if it is 30-40w per square foot, but the entire tent is not used, how will this impact the plant. Conversely, if I have 80w per sqaure foot (assuming heat is not an issue) will the plant grow that much/better faster? Any information would be appreciated. Thanks


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## orangesunshine (Jun 17, 2015)

light is typically measured in lumens or footcandles---in many cases more light the better more vibrant growth---200 to 400 watts per sq ft will give you greater coverage----also gives deeper penetration thru the canopy and better development of the lower flowers---type of lighting is a different topic---vegging plants prefer blue spectrums---flowering plants prefer orange spectrums---imo---best bang for your buck running HPS thru the entire life of the plant---there are a few here that runn 1000w in their tents


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## Locked (Jun 17, 2015)

grodude said:


> I often read that when choosing lighting for a grow room one should aim for a minimum of 50w per square foot. I was curious what the impact is if more or less light is used. If, for example, 40w per square foot is used will the plants grow too slow making it a waste of electricity, or will it simply not reach all parts of the plant. What if it is 30-40w per square foot, but the entire tent is not used, how will this impact the plant. Conversely, if I have 80w per sqaure foot (assuming heat is not an issue) will the plant grow that much/better faster? Any information would be appreciated. Thanks



That is an older benchmark I believe that is no longer used.  I always recommend 3000 lumens per square foot for Veg and 5000 for Flower.  That being said I would always shoot for around 7500 lumens in Flower since 5000 is the minimum. jmo


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## grodude (Jun 17, 2015)

Hamster Lewis said:


> That is an older benchmark I believe that is no longer used.  I always recommend 3000 lumens per square foot for Veg and 5000 for Flower.  That being said I would always shoot for around 7500 lumens in Flower since 5000 is the minimum. jmo



I would have the same question about using more/less lumens per square foot and the impact that has on the plant


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## WeedHopper (Jun 17, 2015)

A minimum of 3000 lums for veg and a Minimum of 5000 lums for Flower.
T5s work best for Vegg and Hps or LED for Flower.


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## Locked (Jun 17, 2015)

grodude said:


> I would have the same question about using more/less lumens per square foot and the impact that has on the plant



Well lucky for you I have run less and more light in my 4x4 Flower Tent and can say without a doubt when I hit the Minimum of 5000 lumens a square foot the plants on the outer edges of the center were long and lanky and did not develop as much bud or bud that was as dense.  It was the reason I added more light.   More light won't make them grow faster but will make them produce more yield and the yield will be higher quality. jmo


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## WeedHopper (Jun 17, 2015)

Hamster knows his stuff. I agree totally.


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## orangesunshine (Jun 17, 2015)

1000w eye hortilux HPS bulbs boast 145000 lumens


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## grodude (Jun 17, 2015)

Hamster Lewis said:


> Well lucky for you I have run less and more light in my 4x4 Flower Tent and can say without a doubt when I hit the Minimum of 5000 lumens a square foot the plants on the outer edges of the center were long and lanky and did not develop as much bud or bud that was as dense.  It was the reason I added more light.   More light won't make them grow faster but will make them produce more yield and the yield will be higher quality. jmo



That makes perfect sense. What if I use less lumens than necessary during veg? My understanding of what you are saying is that this would not slow down growth, depending on how low I dropped in lumens, and because I am not in flower it would not affect bud growth. An example would be 250w in an 8-9 square foot tent. Is my understanding correct?


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## Locked (Jun 17, 2015)

grodude said:


> That makes perfect sense. What if I use less lumens than necessary during veg? My understanding of what you are saying is that this would not slow down growth, depending on how low I dropped in lumens, and because I am not in flower it would not affect bud growth. An example would be 250w in an 8-9 square foot tent. Is my understanding correct?



Less lumens(watts) in Veg would not be a good thing either.  It would produce longer lanky plants with too much space between nodes.   You want short squat plants in Veg because they will sometimes double or even triple in size during flower.


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## WeedHopper (Jun 17, 2015)

3000 LUMENS,,,,,min vegg,,5000 LUMENS,,,min flower.:48:


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## The Hemp Goddess (Jun 17, 2015)

grodude said:


> That makes perfect sense. What if I use less lumens than necessary during veg? My understanding of what you are saying is that this would not slow down growth, depending on how low I dropped in lumens, and because I am not in flower it would not affect bud growth. An example would be 250w in an 8-9 square foot tent. Is my understanding correct?


 
No, it is not.  While it may not slow down growth, that statement is dependent on how you define "growth".  What happens when you have less light than you need is the plant stretches more.  This results in larger intermodal spacing.  So while 2 plants could be the same height, a plant that has adequate light that is 3' tall and a plant that has had inadequate light during vegging that is also 3' tall, could have far less bud sites and therefore yield far less.

The main reason that we do not use wattage per sq ft is that different types of lighting vary widely in the number of lumens per watt that they emit.  While 50 watts psf of HPS is usually more than 5000 lumens psf, 50 watts psf of CFLs is about 1/2 of what you need.


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## vostok (Jun 17, 2015)

Correct it you go down this path, aim for 100w psf for the first light, centered above, then budget 50w psf, after that, many moan about the Lumen being for humans only, and whats important is PAR, but many lights these days do have considerable 'Photosynthetically active radiation' (PAR)response rate anyways. (meaning light often include red and blue light in either cool whites or warm whites to some degree)
250wHPS is too small for many grows,tho good for mother plants the heat kicked out is far above any 600w or 400w HPS/Mh included, given lumen per watt ratio ..good luck


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## umbra (Jun 17, 2015)

orangesunshine said:


> 1000w eye hortilux HPS bulbs boast 145000 lumens


 Well for about 20 minutes it is at that level, then it looses 10% of output and drops off to 40% less by about 3 months. This is why many grower replace their bulbs after every grow.


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## orangesunshine (Jun 18, 2015)

umbra said:


> Well for about 20 minutes it is at that level, then it looses 10% of output and drops off to 40% less by about 3 months. This is why many grower replace their bulbs after every grow.




hello umbra   :48:   of course bulbs lose their output over time while still burning the same amount of power---curious to know where you got those specs for the hortilux from?


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## David_willis (Jun 18, 2015)

Depends on the efficiency of the lighting setup. Slightly less light wouldn't be a waste, growth would just be slower. Too much light will result in bleaching and burnt plants.

50w/ft^2 is a good rule of thumb with most light sources. Cfl would need slightly more, high efficiency cobs slightly less. It is a very broad sense of things though.


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## umbra (Jun 18, 2015)

I don't think you will find those specs published. Hortilux simply lists the life of the bulb to complete failure and not degraded performance. What works well for lighting a warehouse, does not equate with growing performance. The references are from a friend of mine who did the research, he is in charge of light measurements for NIST. He did the research for people like me, lol.


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## The Hemp Goddess (Jun 18, 2015)

David_willis said:


> Depends on the efficiency of the lighting setup. Slightly less light wouldn't be a waste, growth would just be slower. Too much light will result in bleaching and burnt plants.
> 
> 50w/ft^2 is a good rule of thumb with most light sources. Cfl would need slightly more, high efficiency cobs slightly less. It is a very broad sense of things though.


 
I'm sorry, but this is incorrect.  Inadequate light does not slow down growth--it causes stretching.  The plant will most likely be the same height under adequate light and underlit--the difference is in the internodal spacing.

And it is hard to get too much light.  I generally try and run at least 7500 lumens per sq ft.  Lights that are too intense cause bleaching and too much heat, not too much light, causes burning.

And it is the differences in light that makes x number of watts psf a useless number.  With CFLs you do need to get close to 100W per sq ft.  With LEDs we have been told we want to strive for 60 working watts per sq ft.  (but we were also told that we should be able to run 50% of the wattage we use for HIDs, so that statement is somewhat ambiguous).  The 600W HPS you can run under 50 watts per sq ft.


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## orangesunshine (Jun 18, 2015)

umbra said:


> I don't think you will find those specs published. Hortilux simply lists the life of the bulb to complete failure and not degraded performance. What works well for lighting a warehouse, does not equate with growing performance. The references are from a friend of mine who did the research, he is in charge of light measurements for NIST. He did the research for people like me, lol.






NIST?----Wish I had a friend with a light meter.....those stats sound so harsh....are all bulbs created equal?---same scenario  as driving a new car off the lot...lol...be well...please pass my regards


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## umbra (Jun 18, 2015)

He did some graphs I'm trying to copy. MH bulbs fall off a lot quicker than HPS. Even within HPS bulbs there were variations. I don't think he tested every bulb out there, but it looked 4 different manufactures' bulbs. Hortilux was 1 of them. I use hortilux bulbs and I wanted to know if they were worth the extra money, so he did the test. Of the HPS, Hortilux was much better at color retention. That is an early sign of degradation of the bulb.


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