Re: MH wattage per plant

pdgenoa

pdgenoa

Member
I've been trying to get a straight answer to a simple question for a few weeks but everywhere I've looked the answers are argumentative or not addressing the question.

Here it is: *as a general rule* how many watts per plant when using an MH bulb?

I don't want watts per square foot.
I don't want lumens per plant.

This is for four, potted autoflowers if that helps.

A simple answer (in as much as that's possible) would really be appreciated. Thanks.
 
Richard Drysift

Richard Drysift

Well-Known Member
A simple rule of thumb for high intensity discharge lights like an MH or HPS is to have at least 100 watts for every plant. I didn't make this up it is something I read in an Ed Rosenthal book many years ago. So if you got 4 plants you should have at least a 400w light. That doesnt mean you cannot have more or less plants it's just that 100 watts per plant is considered adequate. It's only a guideline to help decide what lighting you will need. Led and/or other types of lighting differ greatly than hids in output so the guidelines go right out the window in that case.
 
Gquebed

Gquebed

Well-Known Member
Richard Drysift said:
A simple rule of thumb for high intensity discharge lights like an MH or HPS is to have at least 100 watts for every plant. I didn't make this up it is something I read in an Ed Rosenthal book many years ago. So if you got 4 plants you should have at least a 400w light. That doesnt mean you cannot have more or less plants it's just that 100 watts per plant is considered adequate. It's only a guideline to help decide what lighting you will need. Led and/or other types of lighting differ greatly than hids in output so the guidelines go right out the window in that case.
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Sounds like that would be a minimum for bare survival, unless they were very small plants.
 
Kerovan

Kerovan

Well-Known Member
There is no straight answer. Coverage matters. You cannot give an accurate "per plant" figure. How close together are the four plants? How big are the plants? What matters is the area you are growing them in and the type of hood and dispersal pattern. In a 4x4 tent and 600W light would be good with a good wide hood that disperses the light well. If it's in a small hood that doesn't disperse well it would only cover a 3x3 area or possibly even smaller.

How big is the area you are growing in? It can be better a lot of times to have 2 weaker lights for better coverage than one big light with less coverage.
 
pdgenoa

pdgenoa

Member
Richard Drysift said:
A simple rule of thumb for high intensity discharge lights like an MH or HPS is to have at least 100 watts for every plant. I didn't make this up it is something I read in an Ed Rosenthal book many years ago. So if you got 4 plants you should have at least a 400w light. That doesnt mean you cannot have more or less plants it's just that 100 watts per plant is considered adequate. It's only a guideline to help decide what lighting you will need. Led and/or other types of lighting differ greatly than hids in output so the guidelines go right out the window in that case.
Click to expand...
Thank you. I'd found the basics for cfl's but couldn't seem to find anything specific to hps or mh lights but I knew it was different than the cfl's.
 
pdgenoa

pdgenoa

Member
Kerovan said:
There is no straight answer. Coverage matters. You cannot give an accurate "per plant" figure. How close together are the four plants? How big are the plants? What matters is the area you are growing them in and the type of hood and dispersal pattern. In a 4x4 tent and 600W light would be good with a good wide hood that disperses the light well. If it's in a small hood that doesn't disperse well it would only cover a 3x3 area or possibly even smaller.

How big is the area you are growing in? It can be better a lot of times to have 2 weaker lights for better coverage than one big light with less coverage.
Click to expand...
Thanks for the details. I had a feeling it might not be as simple as I'd have liked.

It's an air cooled hood - about 20"x12" with a 600w mh/hps bulb (have both for doing autoperiods) with an adjustable ballast (50/75/100%).
The tent is 48"x36"x70" and the four plants are close together in 5 gal pots filled about 85% full.
 
jimihendrix1

jimihendrix1

Well-Known Member
While you may not want to use W per Sq/ft. Its easiest, and probably most accurate.

You have 12 sq/ft, and a 600w light

Its said 40w is Minimum amount for veg a plant. 50 minimum for flowering.

At 12 sq/ft you are right at 50w/Sq/ft

At 3 x 3. 9 sq/ft, you are at 66w Sq/Ft. A

At 5 sq/ft your at 120w sq/ft.
 
Kerovan

Kerovan

Well-Known Member
pdgenoa said:
Thanks for the details. I had a feeling it might not be as simple as I'd have liked.

It's an air cooled hood - about 20"x12" with a 600w mh/hps bulb (have both for doing autoperiods) with an adjustable ballast (50/75/100%).
The tent is 48"x36"x70" and the four plants are close together in 5 gal pots filled about 85% full.
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That hood and light combo sounds optimal to me for the tent size. Sounds like you are good to go with either autos or photoperiod plants with great results.
 
pdgenoa

pdgenoa

Member
Kerovan said:
That hood and light combo sounds optimal to me for the tent size. Sounds like you are good to go with either autos or photoperiod plants with great results.
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Thank you. I'm starting to feel better about the setup now. I take pictures of all my steps like crazy and I need to put up a journal. I'm about three grows in now so it's just a matter of organizing them and uploading. Keep putting it off lol.
Thanks.
 
pdgenoa

pdgenoa

Member
jimihendrix1 said:
While you may not want to use W per Sq/ft. Its easiest, and probably most accurate.

You have 12 sq/ft, and a 600w light

Its said 40w is Minimum amount for veg a plant. 50 minimum for flowering.

At 12 sq/ft you are right at 50w/Sq/ft

At 3 x 3. 9 sq/ft, you are at 66w Sq/Ft. A

At 5 sq/ft your at 120w sq/ft.
Click to expand...
I really appreciate that. I've been resisting figuring it out for some stubborn reason but your guide there is too simple for me to make excuses anymore haha.

Someone should make a simple excel guide or something so you can just go down, enter your info and get wattage. I might have to play with that idea.
Thanks again.
 
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Kerovan

Kerovan

Well-Known Member
pdgenoa said:
Thank you. I'm starting to feel better about the setup now. I take pictures of all my steps like crazy and I need to put up a journal. I'm about three grows in now so it's just a matter of organizing them and uploading. Keep putting it off lol.
Thanks.
Click to expand...
Taking notes if very important so that you know what you did right and what you did wrong so you can learn and improve.
 
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