What height to mount 2 x Radion XR15's over a RedSea Reefer 250?

Discussion in 'Aquarium Lighting By Dana Riddle' started by Giraffe0621, Sep 25, 2017.

  1. Giraffe0621

    Giraffe0621 Well-Known Member R2R Supporter Build Thread Contributor

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    Friend is coming to help hang lights (2 x XR15's) tomorrow. Question is how high should I hang them? BRS lists the recommended spread for this light as 18" x 18" and I have two, but that doesn't help me decide how high to hang them, right? Do I need to have a PAR meter to figure that out? Is there a standard height to hang them?

    The Reefer 250 tank is 21" H x 35.5" W x 20" D.

    Thank you for any advice!
     

  2. Larry L

    Larry L Well-Known Member Partner Member 2018

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    I have two XR15's over a tank that is roughly the same size (36 x 24 x 18 tall), and they are mounted on the standard Radion RMS mounting arms, which puts the lights at about 9 inches off the water surface. The coverage is pretty nice with that setup, although I still had more light spillage out the sides than I wanted, so I swapped in the 80 degree lenses instead of the 120 degree lenses (mine are G3s, not sure if that is possible with the G4s). The 80 degree lenses create a little more of a spotlight effect directly under each XR15, but keeps more of the light focused inside the tank instead of on the tank walls.

    You probably don't want them lower than 9" off the water, partly for safety reasons and partly to have room to work in your tank. The higher you mount them, the more overlap you'll get of the two fields of light and probably the more uniform the distribution will be, at the expense of possibly spreading the light out past the edges of your tank. You'll need to turn the intensity up a notch to keep the same PAR at the sandbed as if they were mounted lower, but that's not really an issue because most people aren't running them at anywhere near 100% anyway.
     
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  3. Giraffe0621

    Giraffe0621 Well-Known Member R2R Supporter Build Thread Contributor

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    thanks for the reply @Larry L -- what kind of coral are you keeping in your tank? I think I'm eventually aiming for an SPS-dominant tank, so trying to figure out what would be best for them.
     
  4. Larry L

    Larry L Well-Known Member Partner Member 2018

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    SPS, and LPS mostly on the sandbed. I run my lights at about 25% intensity.
     
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  5. mcarroll

    mcarroll Well-Known Member R2R Supporter R2R Excellence Award

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    Side by side just like Red Sea has the Hydra26's they spec for it. :)
    [​IMG]

    But if you're hanging them and starting from scratch, some triangle math can get you started with the position (80º lenses will be assumed to be 90º lenses for easy math).

    Requirements:
    • you need to cover 35.5 x 20" of tank surface
    • ideally you'd like a 20" diameter of coverage from each fixture for maximum effect, but without spilling light outside the tank
    90º lenses are mathematically unique because the mounting height from the water = the coverage radius. Radius x 2 = diameter.

    So @Larry L's recommendation of 9" is just about right. I'd have said 10" to get 20" of coverage....more or less the same.

    Start there and experiment – see if wider or closer placement seems nicer. Or maybe a little higher or lower.

    USE A LIGHT METER WHILE YOU WORK – AT LEAST A LUX METER LIKE I HAVE. (They're only $12 or so, including shipping!)

    Please don't eyeball it and guess. A light meter is too cheap. :)
     
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  6. Larry L

    Larry L Well-Known Member Partner Member 2018

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    I agree with @mcarroll about using a meter to set your intensity, but in this case it really doesn't come into play as far as light placement - two XR15's over that size tank have way more than enough power to light things up even if they were high above the tank. If you were using weaker lights, then you might have to worry about putting the fixture at the right height for getting the intensity you want. But I'd say play around with the height to get the coverage and overlap you want, and _then_ use a meter to see what kind of intensity you need to run at.
     
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