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Thread: calculating growing space with metal halides

  1. #1
    swords's Avatar
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    Apr 2002
    Cernunnos Woods
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    I have several different currently unused metal halide ballasts
    175 Watt
    250 Watt
    dual 400 Watt (runs two independent 400W MH bulbs) can be used over one enclosure or over two seperate enclosures-depending how I mount the sockets.

    Each bulb I have is 5500K or 6500K color temp.

    Is there a way to calculate how much growing space each bulb will give me and how high should the bulbs be hung above the plants? 3 - 6 feet? I know the intense heat will cause dryness of the air but a humidifyer and fan should take care of it.

    Thanks for your thoughts!

  2. #2

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    Jul 2002
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    Couple of remarks:

    First, be really careful if you have the light(s) and/or ballast in the same area as the plants
    themselves. Obviously, you don't need me to point out to you the manifest problems which
    arise upon the mixing of water and electricity! However, in addition to this clear hazard, it
    is also the case that humidity will rust the light fixture, and could even result in the bursting
    of your bulb!

    Secondly, and to address your question directly, I know that you can illuminate an area of
    about 1.8 m by 2.4 m quite well with a 1000 W HID lamp at about 1 m, and secondary
    illumination (enough for a lot of low-light plants) is about 2.5 m by 2.5 m. You may have
    to experiment a bit to determine the limits of your particular equipment, or consult a
    specialist at a hydroponics store. FWIW, however, you can probably figure it out to your
    satisfaction by just running the equipment and "eyeballing" it to deduce the area reasonably
    well illuminated. And, if you are burining your plants, you may be able to use shade cloth
    to reduce the intensity of the light, provided, of course, that you don't have the shade cloth
    in such proximity to the light to raise the possibility of its ignition!!

    In any case, good luck! I think you will find that this is a good way to grow these plants.
    I use such equipment for my highland Nepenthes and it has served me well for years.

  3. #3

    Join Date
    Dec 2001
    Munich/ Germany
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    I would go for the 5500k bulb which does produce more natural light than the 6500k bulb, but the difference won't be much. I'm using a 70W/4200k metal halide lamp for a 120cm x 60cm terrarium (mostly highland Nepenthes). Light levels are much higher than before with 80W fluorescent growth lights which were also sufficient - but I do have to mention that my plants get high natural light levels at daytime and additional light is only really needed when the days get shorter in winter.


  4. #4
    Aspidistra Pilot mato's Avatar
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    Aug 2011
    Cascadia Subduction Zone
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    Sooo, did you ever come to a decision on this, Josh?
    Truth as Circe. Error has transformed animals into men; is truth perhaps capable of changing man back into an animal?

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