Lumens Per Plant

Discussion in 'Growing Marijuana Indoors' started by nick1409, Feb 8, 2010.

  1. Im a little confused on this, i have people saying you need 2500-3000 lumens per sq ft. i made a one sq ft grow tent with black bags to keep light in, i have 2 23 watt cfls putting out 3200 lumens, but i also here people saying that when you flower you need a good 25,000 lumens. Is this true?
  2. uh I've read 5k lumen per plant. Any way you slice it, you need more lights man.
  3. ^This. 5k at a minimum.

    I would strongly caution against running lights, even CFLs, inside a tiny tent made of plastic bags. The CFLs can get warm enough to melt the plastic onto the bulb, possibly start a fire. You need to figure out a better grow op, safety first.
  4. ok well is that 5k per sq foot, or per plant? cause id wanna fit as many plants as possible into one sq ft.

    and yes in that case i will change the material of the tent
  5. your going to have a tough time having even 1 plant in that tiny area, i would upgrade to a bigger size text
  6. #6 2Lazy, Feb 8, 2010
    Last edited by a moderator: Feb 8, 2010
    My plants are larger than 1 sqft after 3 weeks... so yeah, you're looking at 1 plant maximum, and even then...

    The thing about light and lumens and watts and all that is it isn't really as simple as X number of lumens per Y. There are some general guidelines for people. The idea I'm trying to get across is that the closer to the light source you are then the more lumens you'll have, and also more photosynthetically active radiation (PAR) which is what you're really after.

    Lower wattage light sources need to be kept VERY close to the plant in order to supply a good amount of PAR. As a guideline you need to keep your lumens at over 2,000 to keep photosynthesis rolling, but anything over 15,000 lumens won't be used unless CO2 is supplemented.

    Something conceptual to keep in mind is that a 400w HPS offers around 40,000 lumens 6 inches from the bulb and only 2,500 lumens 24 inches from the bulb. So, any plant more than 2 feet from the bulb won't get enough light to grow.

    With CFL this is more important to understand because they commonly run under 30w. Higher wattage CFLs offer much more heat in exhange for limited casting range so I find lower wattage bulbs to be better suited. A low wattage bulb offers a few thousand lumens around 1" to 2" from the bulb. By the time you reach 3" from the bulb you can cut the number of lumens by 1/4, and generally this isn't enough light to encourage photosynthesis.

    So, the moral of the story here isn't the number of lumens that you should be interested in. It is a combination of how close you can place the light and how many lumens it offers. Then you have to factor in heat and growth height.

    Personally I like to go by wattages. You need at least one 27w day light 6500K CFL for the first week of your plants life. Then you'll need another one. Then you'll need a 23w soft white 2700K CFL. Then 2 more 27w day light bulbs, and finally a 46w soft white 2700K. In total this adds up to about 175w total and you can grow some real bud with it. You could also choose a 150w sun system HPS with maybe a supplemental day light CFL or two. You also have the option of a 90w LED (kept within 2cm of canopy) in such a small space.
  7. #7 nick1409, Feb 8, 2010
    Last edited by a moderator: Feb 8, 2010
  8. You can use the 3500K bulbs if you choose but they produce the most of the wavelength that plants absorb the least of. I would suggest only using a few of those bulbs and adding the appropriate blue and red wavelengths.

    And yes, that bulb would work... in a 400w HID system. That bulb requires a special socket and a special ballast to provide the right electricity to the bulb.
  9. yea i was looking at ballast, haha waaaay to much money for me

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