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plant lights 18000 K vs 6500K

This is a discussion on plant lights 18000 K vs 6500K within the Aquatic Plants forums, part of the FreshWater Topics category;
i just went out to home depot today and bought a double fixture for a 36inch tank.  I purchased a ...

  1. #1
    Teenie Weenie Fish
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    Post plant lights 18000 K vs 6500K

    i just went out to home depot today and bought a double fixture for a 36inch tank.  I purchased a 5000K bulb and a 6500K bulb.  I used to have a single 18000 K power glo bulb on there but have no success with keeping plants.  It says the bulb is good for plants but after reading articles here, i think it is way to high(kelvin) for any plants.  Do you think that 6500s or 5000s are better for plants?

  2. #2
    Large Fish Backdraft Bagel's Avatar
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    Post Re: plant lights 18000 K vs 6500K

    Between 5000K and 12000K is supposed to be a good range for plants (I think. Someone correct me if I'm wrong). I use a combination of 6500K Blue Actinic and a 10000K white, all power compact lighting.
    All roads lead to infinity

  3. #3
    ronrca
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    Post Re: plant lights 18000 K vs 6500K

    "The Kelvin (K) temperature is an approximation of the color of the light (the higher the bluer, the lower the redder). It is supposedly the color of light that a black body (a piece of metal) will radiate if heated to that temperature, but it's not very precise when applied to lamps other than incandescent. It does not say anything about the spectrum of the light.
    So, the difference between 10,000K and 3,000K degrees shows up most as the color of your tank. You can't say if a bulb is good for plants from just the color temperature. Daylight is about 5500K color temperature."

    Quoted from http://www.geocities.com/Heartland/Hills/2637/faq.html#Kelvin

    So, take into account the above, the 'K' rating is not very accurate for fluorescents. Using the daylight value of Kelvin, 5500K, I would think the fluorescents around this 'k' would be enough to grow plants. A more important consideration is not the 'k' value but the output or intensity in lumens/lux.

    Therefore, a 'K' rating of 6500k would be great for growing plants especially if you can get 4 watts/gallon. Im not sure if I would go below 5500K though. I believe that most cheap cool white tubes found are hardware stores are 6500K (so who says expensive 'plant-gro' tubes are better?).

  4. #4
    Large Fish Backdraft Bagel's Avatar
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    Post Re: plant lights 18000 K vs 6500K

    Doesn't color imply spectrum in reference to lightwaves?
    All roads lead to infinity

  5. #5
    ronrca
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    Post Re: plant lights 18000 K vs 6500K

    It might be a little difficult to understand but 'K' is a measurement. This measurement is determined by the following: "It is supposedly the color of light that a black body (a piece of metal) will radiate if heated to that temperature."

    So, in other words, you take a piece of black metal and heat it up to a specific temperature and it will emit a color of light. That temperature would then be the 'K' rating for the matching color that a tube would give off.

    Spectrum on the other hand is the wavelengths produce by a light source. Unlike Kelvin, it is measured in wavelenght such as nanometers and yes, spectrum does make a difference in what colors it will emit. They would be related to each other because the more you heat up the piece of black metal, it would emit different wavelengths. However, remember that daylight is only 5500K and that would be all plants really need. Again, it comes down to the intensity of the light source, because the tubes you usually buy fall into the 'daylight' catagorie.

  6. #6
    Moderator Avalon's Avatar
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    Post Re: plant lights 18000 K vs 6500K

    Yes, ronca and Backdraft are correct. The temperature (K) is not a very good measurement for light spectrum. You need a peak in the red and blue range to properly activate chlorophyll A & C. I do go by the Kelvin temp scale when I'm choosing lights, as there is a slight correlation. Most grow lights contain a "reddish" color bulb (around 5-6K). This is good for nice wide and bushy leaves. Daylight and actinic bulbs are more blue (well, actinic is, duh), but we can't percieve the blue in the 10K bulbs. They just look white to us. Bluer lights will stimulate taller growth in your plants. That's why it's important to have a good mix of lighting on your tank.

    Since you bought a flo-light fixture, I would recommend the following bulbs:
    GE Plant and aquarium (very red bulb, white and blue packaging)
    GE Sunshine (Chroma 50, neutral color, solid orange packaging) I really like this bulb.

  7. #7
    Super Fish Matt Nace's Avatar
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    Post Re: plant lights 18000 K vs 6500K

    More blue with red is the best , Algae likes the red better though, so the florescents spectrom shifts more red as they burn out.

    I love(d) the GE sunshines. I use 3 to 1 Ge plant bulb.

    I dislike the power glows a lot.
    -=Matt=-

    Current tanks:
    125 gallon Mixed cichlid tank
    150 gallon African Mbuna tank
    55 gallon African Mbuna tank
    75g Bubblebee and Demasoni African cichlid tank

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