How much CMH wattage is reccomended for a 4x4 tent

eyesdownchronic · Feb 14, 2021

About how much CMH wattage is recommended for 4x4 without CO2? Seems like the general reccomendation is the 630w but that seems a bit excessive...

I've seen people say that a 600 w HPS is replaceable by 315 w of CMH, which would imply that 630w CMH equals about 1200 W of HPS. That would be way excessive for a 4x4 area without CO2. (obviously the heat would from HPS would be an issue too, but even from a PPFD standpoint 1200w of HPS is probably too much. )

After using both 315 w and 630w almost feels like something in the middle would be ideal. The 630w definitely yields heftier flowers than the 315, but couldn't say its 2x.

**edit: Plant response curve to light is linear for the first part before it starts to plateau out. So after a certain point the more light you supply you begin to receive diminishing returns to growth. Wonder what that most efficient point is...

Anyone have any thoughts or experience?

zachrockbadenof · Feb 14, 2021

i have 2 315's (phillip bulbs) in a 4x3.5ft tent, and didn't think is was enough lite - i have some cheap led's (4) which i added for side light - maybe its overkill, but for sure the buds are not as large as when under a 1000w hps...

Sunshineinabag · Feb 14, 2021

Are there light meter tests done on cmh yet? May e two 630 if Zach's exp is par the course

eyesdownchronic · Feb 14, 2021

zachrockbadenof said:
i have 2 315's (phillip bulbs) in a 4x3.5ft tent, and didn't think is was enough lite - i have some cheap led's (4) which i added for side light - maybe its overkill, but for sure the buds are not as large as when under a 1000w hps...

damn, huh. How high above the canopy are your lights? and do you supplement CO2 at all?
thanks for the input

eyesdownchronic · Feb 14, 2021

Sunshineinabag said:
Are there light meter tests done on cmh yet? May e two 630 if Zach's exp is par the course

fuucck, thatd be a lot of light...
1260 w of CMH for 16 sq ft?

flylowgethigh · Feb 14, 2021

A single bulb light is still gonna be brightest in the middle and weak on the edges, isn't it? I think that you are limited by the center buds (temp /power) in that instance. Sorta like the numbers on this picture (first I found, and probably fake, but the same general idea):

zachrockbadenof · Feb 14, 2021

eyesdownchronic said:
damn, huh. How high above the canopy are your lights? and do you supplement CO2 at all?
thanks for the input

the lights are as close as i can get em and not burn the tops- i'm figuring 12/14''- i have an oscillating fan that sits outside the tent cooling the lights- if i raise the lights to 24'' i'm losing toooo much of the penetration ... the other problem is still looking for the 'holy-grail' and i'm growing 6 diff varieties and they are all growing at diff rates- so one light is 5ft from the bottom of the tent, while the other light is 6ft as the plants are taller... no uniformity ....

and no, i don't use co2, as the space is really tight, and even watering them is a bitch and a half...

with the '2' lights that equates to 45 per sq foot, which under ideal circumstances would be mid range of not enough lite and overkill, but i have far from the ideal situation, and the plants on the outskirts of the lights suffer, hence i drop cheap led's to help em along...

one day i wanta have a large full sun outdoor space to grow.... ahhh to dream

noknees · Feb 15, 2021

zachrockbadenof said:
the lights are as close as i can get em and not burn the tops- i'm figuring 12/14'' if i raise the lights to 24'' i'm losing toooo much of the penetration ... the other problem is still looking for the 'holy-grail' and i'm growing 6 diff varieties and they are all growing at diff rates- so one light is 5ft from the bottom of the tent, while the other light is 6ft as the plants are taller... no uniformity. and no, i don't use co2, as the space is really tight, and even watering them is a bitch and a half..

seems like your setup is just a complete mismatch in general for what you're doing. i ran multiple strains (all indica) with only moderate variance in height, and found it a pain.

eyesdownchronic said:
After using both 315 w and 630w almost feels like something in the middle would be ideal. The 630w definitely yields heftier flowers than the 315, but couldn't say its 2x.

**edit: Plant response curve to light is linear for the first part before it starts to plateau out. So after a certain point the more light you supply you begin to receive diminishing returns to growth. Wonder what that most efficient point is...

Anyone have any thoughts or experience?

my 630 has a 490 watt setting the plants seemed to like late in flower, but of course, coverage was an issue. i think that's the "in-between" you're looking for in a 4x4. my main takeaway from that experiment was that if i were to run that setup again, i would run it at full power, all the way on the ceiling, over a single monster plant with long shaved legs. something very serious and worth doing in that style.

eyesdownchronic · Feb 15, 2021

noknees said:
my 630 has a 490 watt setting the plants seemed to like late in flower, but of course, coverage was an issue. i think that's the "in-between" you're looking for in a 4x4. my main takeaway from that experiment was that if i were to run that setup again, i would run it at full power, all the way on the ceiling, over a single monster plant with long shaved legs. something very serious and worth doing in that style.

yeah, my 630 has a 480 setting that ive been considering running it on. Think that 500 level could be close to the sweet spot.

Now thinking about it, running 2 x 315 fixtures like zachrockbadenof could increase how much wattage you could get by reducing light hot spots.

zachrockbadenof · Feb 15, 2021

noknees said:
seems like your setup is just a complete mismatch in general for what you're doing. i ran multiple strains (all indica) with only moderate variance in height, and found it a pain.
.

it is a mismatch, n a pain, but until i find that special lady.... :plant grow:

Zeez · Feb 15, 2021

I used three CMH 315s in a 5 x 9.

overbudjet · Feb 15, 2021

8 315 cmh (elite agro bulb philips)over 4'x11'
Need sunglass to get in :plant grow:

So around 3 315 for a 4x4

zachrockbadenof · Feb 15, 2021

overbudjet said:
8 315 cmh (elite agro bulb philips)over 4'x11'
Need sunglass to get in
So around 3 315 for a 4x4

yeah ... that seems to be about rite... you r around 57+ , i'm around 45, but with the cheap led's it brings me to around 50 , n the plants not directly under the hood get the benefit of the led's

eyesdownchronic · Feb 15, 2021

overbudjet said:
8 315 cmh (elite agro bulb philips)over 4'x11'
Need sunglass to get in
So around 3 315 for a 4x4

damn, i bet. do you run any CO2?

and do you have an approximate GPW from your set up?

interesting to see how high vs. low light set ups compare GPW wise.

overbudjet · Feb 15, 2021

Co2 at 1150 ppm, for the gpw i would say between .65 (on low side)up to 1.25 of AAA primo bud :skiiing:

all the trim and fluffy go to rosin making.

eyesdownchronic · Feb 15, 2021

overbudjet said:
Co2 at 1150 ppm, for the gpw i would say between .65 (on low side)up to 1.25 of AAA primo bud all the trim and fluffy go to rosin making. https://www.icmag.com/ic/picture.php?albumid=32617&pictureid=835783 View Image https://www.icmag.com/ic/picture.php?albumid=32617&pictureid=846939 View Image https://www.icmag.com/ic/picture.php?albumid=32617&pictureid=846938 View Image

oh nice !

thanks for your input! 1.25 gpw sounds really good.

eyesdownchronic · Feb 15, 2021

zachrockbadenof said:
yeah ... that seems to be about rite... you r around 57+ , i'm around 45, but with the cheap led's it brings me to around 50 , n the plants not directly under the hood get the benefit of the led's

not sure if using w\sqft is the best measure...
also, where does that 75 w / sq ft. come from...

if using phillips cmh which has a approx. 2 ppfd/w output. that would be a ppfd of about 2400 for a 4x4. 75*16= 1200 *2 = 2,400 lets say avg canopy level is about 1800-2000 umol/ sec. under a 12/12 cycle thatd be like... 12 * .0036 *1900 = 82 DLI... thats astronomically high. A "sunny" greenhouse is like 20-30 DLI...

overbudjet · Feb 16, 2021

I am not skilled in math and maybe i am a little over on light but my girl love it so :sasmokin:

For the 75watts per sq. ft. (it supposed to be the optimum for hps with co2)those number come from long time ago ,when light where less efficient than today :2cents:

zachrockbadenof · Feb 16, 2021

overbudjet said:
For the 75watts per sq. ft. (it supposed to be the optimum for hps with co2)those number come from long time ago ,when light where less efficient than today

its all confusing... supposely a 315 is equal or exceeds a 400mh- so in my case (4x3.5ft tent), i'd be real close to a 1000watter

now i have grown with 1000wattter's , not in a tent but a small room , and the buds with the big-dog are bigger, and it seems more resin, and the penetration is def better...

if u should have a min of X watts... per sq ft, and a 315 is more powerful then a 400.... well i'm confused....

Greenheart · Feb 16, 2021

eyesdownchronic said:
**edit: Plant response curve to light is linear for the first part before it starts to plateau out. So after a certain point the more light you supply you begin to receive diminishing returns to growth. Wonder what that most efficient point is...

This might help answer that. Ibechillin has an excellent sticky on lighting.

Post #5 has a chart at the bottom stating that a

"DLI of 43.2 mols/m2/d which is ideal for maximum yields according to NASA experiments"

How much CMH wattage is reccomended for a 4x4 tent

Active member

Well-known member

Active member

Active member

Active member

Non-growing Lurker

Well-known member

Member

Active member

Well-known member

---------------->

Active member

Well-known member

Active member

Active member

Active member

Active member

Active member

Well-known member

Active member