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Massaged PAR Data for T5HO lights

Discussion in 'Lighting' started by VaughnH, Jul 19, 2009.

  1. VaughnH

    VaughnH Lifetime Charter Member
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    Since your tank is 18 inches front to back depth, a single row of lights above the tank may not give you the uniformity of light intensity you want all over the substrate. Except for that, a pair of the 55 watt bulbs in a line across the top of the tank, about 20 inches from the substrate, would give you around 45 micromols of PAR at the substrate. (This is based on data from my light, which had bulbs about 18 months old, as I recall, GE9325K bulbs.) I think I would put two rows of the bulbs, spaced about 8 inches apart, and raise the lights to about 6-8 inches above the top of the tank. If you make the "box" the lights are in with long enough "skirts" front and back, you should be able to reduce the light spillover quite a lot. I like to draw a sketch of the cross section of the light, a pair of 5/8 inch diameter circles for each of the bulbs, and graphically figure out how deep the "box" should be to block most of the spilled light. Just remember that the "box" has to be wide enough for the two rows of reflectors.
     
  2. meatus

    meatus Junior Poster

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    VaughnH,

    Thanks for your reply. Does this still apply with the double tube bulb T5's like shown here? They are 22" long and 4" wide. I guess depending on how long the skirts need to be to block most of the light spill I might as well just make a hood since it would only have to be 10" from the top. Although a hood that big wouldn't look nearly as good.

    [​IMG]
     
  3. VaughnH

    VaughnH Lifetime Charter Member
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    Those are the AH Supply light kits I was referring to, but be sure to get the one that lets you put the bulbs end to end. This type:
    [​IMG]
    That will let you separate the two rows far enough to get the uniformity of lighting that is desirable.
     
  4. meatus

    meatus Junior Poster

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    Yeah those are the ones I have I just didn't browse their website long enough to find a better pic. Thanks again Vaughn for your help!
     
  5. Gerryd

    Gerryd Plant Guru Team
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    Small data sample:

    T12 2x30w Verilux

    Mounted 6" above the surface over the middle of the tank. Basic Perfecto/all glass reflector w/ dual bulbs.

    I get about 45 PAR just below the surface. 25-30 at mid water, and about 15-20 down near the substrate.

    This is on a 45 gal tank, 36x18x12.

    The readings are pretty average/stable at the horizontal level moved to different corners, etc. I attribute this in part to the better spread of the twin bulbs and the increased distance above the tank.

    I know these bulbs are at least 1 year old as well. No cover glass open top tank.

    No c02 or ferts or WC. Just top off evap and feed. I have anubias flowering at 18-20 PAR.

    So, not much is needed for low light, low maintenance tanks....
     
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