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Light Calculator questionable?

Discussion in 'Rotala Butterfly Support & Feedback Forum' started by tiger15, Aug 12, 2017.

  1. tiger15

    tiger15 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 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 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
    Last edited: Aug 19, 2017
  6. VaughnH

    VaughnH Lifetime Charter Member
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    I know of no accurate way to calculate how much light intensity you will get from a specific light fixture for a specific set-up. You can estimate the intensity and probably be in the right ballpark, but there are far too many variables to accurately calculate it. The best thing is to select a light fixture which a rough guess tells you will give you more than the light you want. Then borrow a PAR meter and measure the PAR at several distances from the light, measuring at the middle of the light. Plot those numbers as PAR vs Distance and pick out the distance that gives you the PAR you want. Design your light suspension method, or light feet, etc. so you will have the light at the right distance to get the PAR you want. Keep that plot, so if you want to change the intensity you will know how much to change the distance to get that specific PAR. If you find that your light fixture gives much too much light, make a neat screen from gray fiberglass window screening, that attaches to the light fixture - this will drop the PAR by 40%. Keep in mind that the water in the tank has little effect on the PAR at any distance under 30 inches or so. In fact the water slightly focuses the light so in water you can get slightly more PAR than in air.

    For now at least you can borrow a PAR meter for the cost of shipping and insurance, so this is both an accurate and an economical way to get the PAR you want. See: https://barrreport.com/threads/apogee-par-meter-for-rent.14334/
     
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  7. Jason King

    Jason King barrreport.com
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    As @VaughnH said :)

    The light Calculator is a basic guide and is all based from users information i.e @VaughnH charts and other reads on the internet etc.. but unless we have access to and are able to test ever single lighting fixture out there it's impossible to be 100% accurate.

    If users or manufacturers would like to send us these fixtures to test we would happily test them but until then it's almost impossible to be perfect.
     
  8. Jason King

    Jason King barrreport.com
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    We could also create a dedicated thread and collect the info from users? Then rework the Calculator based on this data?

    • Name of Fixture:
    • Distance from Substrate:
    • Par Readings:
    • Etc:
    • Etc:
     
  9. tiger15

    tiger15 Member

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    The light calculator is modeling, not a weight and measure calculation, so it won't be precise because it is a function of many variables. But it doesn't need to be precise as long as it can estimate the correct ballpark figure to judge if one has low, medium or high light regime. If accurate, It is a valuable tool because access to a PAR meter is not easy or too pricey for one time use.

    The light calculator is improvable with actual data input from users for calibration. The estimates are reasonable for older, established lights, but a challenge for LEDs which are still evolving. Presently, the calculator is calibrated with three types of light: Cree, EcoSmart and BML. BML strip is no longer for sale, so it is irrelevant. Cree and EcoSmart are large bulb, not strip LED commonly used in aquarium. The uncertainty is guessing the right LED light for one's set up, which can change the outcome by ballpark figures from low to high light regime.
     
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  10. VaughnH

    VaughnH Lifetime Charter Member
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    This is a unique time in our hobby history! Access to a good PAR meter is easy and not expensive today, and for some uncertain number of days to come. https://barrreport.com/threads/apogee-par-meter-for-rent.14334/ So, why not take advantage of it??
     
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  11. tiger15

    tiger15 Member

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    Make it mandatory that whoever borrow the PAR meter must submit the data to Jason to update the light calculator.
     
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  12. Christophe

    Christophe Subscriber
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    Even then there are other variables -- Hardscape or a tall stand of stems that throws shade, dark vs. light-colored substrate. Direct measurement at least is the best way to establish a trend for a given fixture if several people have the same type.
     
  13. Jason King

    Jason King barrreport.com
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    I'm going to create a dedicated thread for this and a form that will allow members to submit the data.

    @VaughnH as you are the light master ;) could you please list all Requirements for the form.

    I.e
    Fixture Name
    Fixture Size
    No# of Bulbs
    ??
    ??
    Distance at 6"
    Distance at 12"

    Etc.

    Once I have all this data I'll create a form.

    Also I would like to point out that @fablau is the guy that does the the clever backend stuff on the Calculators :) I'm the guy for the frontend GUI stuff, my design and Fabs engine.

    Thanks.
     
  14. Jason King

    Jason King barrreport.com
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    Here is an example of what i can come up with for the data submission, from this we can form a collective and update the calculator as and when the data is submitted.

    this form is far from complete and ill update it properly once i have all the fields required.

    https://barrreport.com/forms/light-calculator-data-form.3/form

    Thanks
     
    #14 Jason King, Sep 6, 2017
    Last edited: Sep 6, 2017
  15. Jason King

    Jason King barrreport.com
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  16. VaughnH

    VaughnH Lifetime Charter Member
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    I think such a form will work best if a different form is used for each type of lighting. For example:
    ......LED Lights.....
    Manufacturers Name:
    Model Name:
    Model Number:
    Distance of light from substrate: (At 100% power)
    Par reading at ____ inches (about 12"):
    Par reading at ____ inches (about 18"):
    Par reading at____ inches (about 24"):
    Fixture Length:

    .....T5HO Lights.....
    Manufacturers Name:
    Model Name:
    Model Number:
    Bulb Type:
    Data is based on how many bulbs?:
    Does the fixture have individual bulb reflectors?:
    Distance of light from substrate:
    Par reading at ____ inches (about 12"):
    Par reading at ____ inches (about 18"):
    Par reading at____ inches (about 24"):
    Fixture Length:

    .....T5NO Lights..... (etc)
     
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  17. Jason King

    Jason King barrreport.com
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    Thanks Hoppy, that makes sense :) ill work on this tomorrow.
     
  18. Jason King

    Jason King barrreport.com
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  19. tiger15

    tiger15 Member

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    There should be optional information, if available, for LED, including (1) Number of diodes, (2) Rated wattage for each diode, (3) Manufacturer's rating of the input wattage, and (4) Manufacturer's rating of the output lumen.

    The optional information is useful in best matching one's LED not in the brand list.

    LED is the light of the future, replacing the once popular CFL. Already 80% of the stocking in home centers are LEDs, so are many LED listing in Ebay.
     
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  20. Jason King

    Jason King barrreport.com
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