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Light Calculator questionable?

Discussion in 'Lighting' started by tiger15, Aug 12, 2017.

  1. tiger15

    tiger15 New Member

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    In my 75 gal set up, I have 3 - 48" LED strip lights with a total of 265 diodes, 112 Watt , and 13416 Lumen.

    Using the light calculator in http://www.rotalabutterfly.com/light-calculator.php, I came up with 204 PAR at substrate level, which will put my light in extremely high light regime. That doesn't sound right as I only have 1.46 watt per gal.

    Did I do something wrong or the calculator is wrong?


    upload_2017-8-12_10-22-21.png
     
  2. Christophe

    Christophe Subscriber

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    Pay more attention to the lumens estimate.

    'Watts per gallon' is kinda meaningless. Light fixtures differ greatly in the efficiency with which they deliver light for the amount of power they use. A T5 fixture out of the box has some given intensity of light it puts out. Install some reflectors in that fixture, and the power consumption doesn't change, but the lighting efficiency does vastly!

    The calculator doesn't sound too far off -- I'm using a single BML 90 degree MC series strip over a tank similar to yours, dialed back to about 70%. Three 60 degree strips on fully is definitely going to be really intense. You'd probably do best to cut it to two fixtures to get decent spread, and dial them back to something like 40-50%.
     
  3. tiger15

    tiger15 New Member

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    I understand that the old watt per gal rule is based on T12 FL bulb which is less efficient than LED. I tried a calculation using 4 T12 FL bulbs, 40 watt each, and came up with only 20 PAR. Does the calculator suggest that my 3 LED strip is 10 times as efficient as 4 T12. That doesn't sound right.

    I tried an alternate light intensity estimation method below that tells me my light is low to medium.

    https://www.monsterfishkeepers.com/forums/threads/lighting-a-planted-tank.73446/

    Which estimate should I believe.

    How I can tell I have too much light? I have never observed pearling and see zero to slow growth in my plants. My LED are cheap light I bought from eBay and I was considering adding more light to promote growth.
     
    #3 tiger15, Aug 12, 2017
    Last edited: Aug 13, 2017
  4. KeeperOfASilentWorld

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    There is a difference between having 265 bulbs on the same unit and having three units working together. Having them separated would probably give you around 10-20% less PAR but with better spread, almost full coverage.

    On bulb type you should be choosing Cree as far as I know. I just tried using the BML60 like you did and I got 759 PAR at substrate for my tank. On Cree, it calculates my PAR at 207 which I find to be very accurate for my tank.
     
  5. tiger15

    tiger15 New Member

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    An uncertainty In estimating the PAR is knowing the true input wattage. Commercial LEDs often select diode type ranging from 0.1 to 3 watts. Multiplying the number of diodes to the diode wattage does not equal to the input wattage, which can be substantially less. In the above case, the calculated PAR is 3.5 times the true PAR (asumming CREE is true), implying the input wattage and/or the calculation is over estimated by a large margin.

    For a long time I thought I have low light, based on less than1.5 watt per gal rule. The calculator shows I have 204 PAR and even discounting the calculation by 3.5 times, my light is still in the 60 PAR high light regime. I don't know what to believe and wish someone can explain the descrepancies and assumptions in the calculation.
     
    #5 tiger15, Aug 19, 2017 at 10:28 AM
    Last edited: Aug 19, 2017 at 4:44 PM
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