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Thread: Lux meters

  1. #1
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    Lux meters

    anybody ever use a lux meter to determine how their light levels are over time???

  2. #2
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    LUX meters are too expensive to use for a one off hobbyist. There is however a calculation to determine LUX values that I have used in the past. I would have to dig it up to post the mathematical equation.
    Rob

  3. #3
    Senior Member Deafboy's Avatar
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    Stange that you ask, because I'm doing exactly that since this week. I just received some new ARC bulbs from Ivan and will evaluate their performance over the coming months. I'm using a homebuilt PAR meter, not a lux meter. I consider PAR a better method of evaluating what corals need than Lux. For this application though, since I'm measuring lamp aging over time, a lux meter would give similar results.

    Michel
    20 g reef, 72 g reef

  4. #4
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    Any info would be greatly appreciated--i am currently running 2-400 watt 20k Reeftech MH bulbs over a 112 gal tank,on electronic ballast, just want to physically know when to replace bulbs

  5. #5
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    I will look it up tomorrow ... OK
    Rob

  6. #6
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    Tanks very much!!!!

  7. #7
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    The info …..
    LUX refers to the intensity of the light provided and it is recommended that a reef tank receive between 10,000 and 12,000 LUX of full spectrum lighting at the surface of the water as a STARTING point. The dirtier or more coloured the water is, or deeper the tank, the more LUX you will need at the surface to deliver good intensity to the bottom of that tank.

    The confirm that you have or will have enough STARTING POINT watts of light to deliver the desired LUX at the surface of a given tank do the math as follows. The information about the bulbs can be obtained from manufactures in most cases.

    Watts needed = L X A divided by E X U
    L is LUX desired over tank
    A is area of tanks surface in sq. meters (total sq. inches divided by 1,550)
    E is bulb efficacy in lumens per watt ( Lumen output of chosen bulb divided by watts of the bulb)
    U is the utilization factor (constant @ 0.5)

    EXAMPLE:
    The tank is 72" X 24" @ 30” deep.
    I want 25000 LUX at the surface because of the depth.
    I think I can use 2 – 250 watt MH bulbs that render 20,500 Initial lumens each as per the manufacture.
    In this example
    L = 25,000
    A = 1.11 sq. meters (72 X 24 divided by 1,500)
    E = 82 ( 20,500 X 2 bulbs) divided by ( 250 X 2 bulbs)
    U = 0.5

    So ….
    25,000 X 1.11 divided by 82 X 0.5 = 27,750 divided by 41 = 676.82 watts
    As you can see in this case I would be short 176 watts and should there for add a minimum of one more 175 watt bulb.
    You can plug in the information on existing setups or intended setups. Bulb CRI should be as high as possible because the math is based on “full spectrum lighting”
    Rob

  8. #8
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    Any idea on initial lumens for the "Reeftech" 400 watt,20K MH bulb?
    I can't find any Specs.

  9. #9
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    Thanks Salty Dog--using your formula on my 60 x 18 x 24high tank i get 692 watts---I am currently running 2-400 watt MH.about 8" above the water, 10 hours a day.
    Still curious though over time the reduction in initial lux.

  10. #10
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    Have you done a web search for the manufacturer? Or a search on bulb comparison results? These are the places where you will have the most luck finding specs.
    Rob

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