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how many watts per plant?

  • by eddyheroin
  • Dec 11 2007 03:10 AM
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Posted 11 December 2007 - 03:10 AM

hey how many watts do you need per plant?
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Posted 11 December 2007 - 03:12 AM

if HID its ideal to have 100 watss per plant

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Posted 11 December 2007 - 03:20 AM

thanks :)

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Posted 04 January 2010 - 02:45 AM

bringing back a old thread, but how many watts per plant would you need for cfl bulbs?
would one 26 watt (100 watt equivalent) bulb be okay for one plant?

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Posted 04 January 2010 - 02:53 AM

bringing back a old thread, but how many watts per plant would you need for cfl bulbs?
would one 26 watt (100 watt equivalent) bulb be okay for one plant?


No, you need to go by the actual wattage. Not the equivalent wattage. So, you need 3-4 26W bulbs per plant if you go by the 100 watts per plant rule.

There is also a school that says 100W for the first plant then 50 W for each additional plant. This is also acceptable although not nearly as effective as the original 100W per plant rule.

Good luck.

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Posted 04 January 2010 - 05:19 AM

With CFLs I would say that 100w actual per plant is the minimum you want. With HID the minimum is about 50w, with 100w being more like ideal.

Since HIDs have a higher lumens-per-watt efficiency than CFLs, there really can't be a single rule of thumb that applies to them both equally.

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Posted 05 January 2010 - 05:18 AM

i like going by lumens since its actually the output of light and not the electricity

i like using 5,000-10,000 lumens per plant i have superb results in these ranges

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Posted 05 January 2010 - 07:12 AM

With HID the minimum is about 50w, with 100w being more like ideal.


So it would be ideal to have 4 plants under 1-400w HID, and acceptable to have 8 plants under 1-400w HID? Or is it possible to have 8 plants under one light?

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Posted 05 January 2010 - 12:17 PM

^That's right. It depends in part on the growing technique -- if you use scrog or LST and have very broad, spread-out plants then you'll need to scale back the number of plants a bit. Ultimately the light has a coverage of an area (sq. footage), so it depends on how much area your plants cover.

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Posted 05 January 2010 - 03:59 PM

So it would be ideal to have 4 plants under 1-400w HID, and acceptable to have 8 plants under 1-400w HID? Or is it possible to have 8 plants under one light?



Vegetative growth requires about 2,500 lumens per square foot and in flowering, plants require about 10,000 lumens per square foot. Ill show you the math, then you can adjust the numbers accordingly. Lets say ur 400w Hid has an output of 53,000 lumens. All lights represent lumens at a distance of 1 foot away from the target, but for an HID system this is of course to close, 2 feet away is more ideal. The Inverse square law is light intensity (output in lumens) divided by distance (distance the target is from the source) squared. So for a 400w (or 430w) system it would need to be about 2 feet from the plant tops. So for a 400w system outputting 53,000 lumens we now know this will be outputting 53,000 lumens divided by 2 foot squared (53,000/2x2) which is 13,250 lumens at the plant tops. So if we wanted to give the plants 2,500 lumens per sq foot for vegetative growth, we need to work out how far the lamp could be away from the source and that would provide us with the sq area. 53,000 lumens at 3 foot is (53,000/3x3) 5,888 lumens, at 4 foot is (53,000/4x4) 3,312 and 5 foot is (53,000/5x5) 2120, so we know that to deliver 2,500 lumens per square foot allows the bulb to be about 4.75 feet from the source which would illuminate a square area of 4.75 x 4.75 or 22.5 sq feet.

Yes if you have 22.5 square feet to work with 8 plants is fine under a 400 watt HID system. It is ideal to have around 1-1.5 sq foot of space per plant. So idealy you can have a 4x2 area and be fine.

Edited by lerner, 05 January 2010 - 04:04 PM.


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Posted 05 January 2010 - 04:14 PM

The amount of watts per plant is EXTREMELY Dependant on the size of your plants. For example, I have 600 watts covering 32 plants. Thats only 20 watts or so per plant. But my plants are very small, usually completing their life cycle in 80 days or so. A better equation is watts or lumen's per sq ft. Ive heard anything from 40 to 100 watts. Generally 50-60 is an accepted range. Most people also agree that over 100 watts per sq ft is a waste, some people even say over 50 is a little overkill.

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Posted 05 January 2010 - 04:19 PM

A better equation is watts or lumen's per sq ft.

Ultimately that's correct, and then take one rule of thumb and apply it to another rule of thumb of number of plants per sq foot. Standard rule of thumb is 1 per sq ft, but that varies depending on the grow technique.

Ive heard anything from 40 to 100 watts. Generally 50-60 is an accepted range. Most people also agree that over 100 watts per sq ft is a waste, some people even say over 50 is a little overkill.

Again, depends on the kind of light. A watt from a 600w HPS gives off way more lumens than a watt from a 23w CFL, more than double in fact. 50 watts per plant is a good minimum for HID, 100 watts per plant is a good minimum for household CFLs.

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Posted 05 January 2010 - 04:21 PM

Ultimately that's correct, and then take one rule of thumb and apply it to another rule of thumb of number of plants per sq foot. Standard rule of thumb is 1 per sq ft, but that varies depending on the grow technique.

Again, depends on the kind of light. A watt from a 600w HPS gives off way more lumens than a watt from a 23w CFL, more than double in fact. 50 watts per plant is a good minimum for HID, 100 watts per plant is a good minimum for household CFLs.


I usually dont consider CFL's effective grow lights cept for clones lol, so I really didnt think about it.

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Posted 05 January 2010 - 04:30 PM

^Fair enough ;)


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