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correct amount of light?

Discussion in 'Lighting' started by oldpunk, Dec 2, 2009.

  1. oldpunk

    oldpunk Guru Class Expert

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    i figure someone who has done some testing with a par meter can get me pretty close so i'm just going to ask...

    how high above my tank should i hang my fixture to achieve the correct amount of light for a non-co2 tank? (29g)

    - the distance from the top of the water to the substrate is 16"
    - the fixture is a 2x24w T5HO with individual reflectors (tek knock-offs)

    (is this even a valid question?)

    thanks

    -josh
     
  2. Biollante

    Biollante Lifetime Charter Member
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    Valid Questions

    Hi Josh,

    It is a valid question, I am not sure I have a valid answer or that my answer would have any greater validity than anyone else s. :eek:

    It seems like a reasonable amount of light, I tend to like lights up off the water at least 8 inches and 12 or 18 being better. That however is just me. ;)

    It depends on what you want, with that much light I might add floating plants or something that put leaves on the surface. :)

    I like plants that grow up out of the aquarium.

    The thing I have found with my PAR meter is that I get more usable light in than I ever imagined.

    I guess the questions are for you. What are you trying to accomplish? Are you using Excel?

    What fish? What plants? What kind of substrate?

    Good luck,
    Biollante
     
  3. shoggoth43

    shoggoth43 Lifetime Charter Member
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    T5HO puts out a LOT of usable light. You're looking at 48W of it over a 29 gallon tank. Also, lamp/bulb choice can make a sizable difference in PAR. You may find you have to raise the fixture quite a bit. For non CO2 simple T12 lights work well enough, just to give you an idea of the brightness requirement.

    Another option while you adjust this is to just get some stem plants and toss them in there floating around. They should block off some of the light while they grow and alleviate some of the hight light issues.

    -
    S
     
  4. oldpunk

    oldpunk Guru Class Expert

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    thanks for the replies guys! sounds like i need to fork over some more info.

    *i'm just gonna list what i think might be relevant to figuring out how high to hang my fixture.

    tank - standard 29g
    substrate - mineralized topsoil with a sand cap(.5-3mm)
    water depth - 16" (from water's edge at the top to the substrate)
    fixture - 2x24w t5ho(homemade*) ice cap reflectors with advance ballast, hagen 6,700K bulbs, light bars let me raise the fixture as high as 2'.
    plants - java ferns, crypts, moss, lotus
    ferts - going to fallow the barr method for non-co2
    excel - i have it but would rather not do daily dosing
    goal - low maintenance/slow growth w/ no stems, no floaters
    fish - sorry, no idea yet

    i think that's about it.

    *the reason for this post - i was hoping that par readings are starting to get predictable. (predictable enough to get me pretty close anyway. i can eye ball it from there :D )

    -josh
     
  5. Biollante

    Biollante Lifetime Charter Member
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    18 to 24 Inches, Me Thinks

    Hi Josh,

    I think that is an excellent selection of plants for your purpose.:)

    The Lotus (What specie?), may be a bit large put will provide a lot of shade.

    Given your plants, I think I would raise the lights 18 inches above the water or perhaps even start at 24 inches and work your way down. ;)

    I would skip the Excel all together.

    I am not sure the PAR meter influences me , yet, other than I have realized how much less ‘wattage’ I need than I used to think. The plants you have along with a little patience could, you could get away with half.;)

    Biollante
     
  6. Henry Hatch

    Henry Hatch Guru Class Expert

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    I am currently running 48 watts of t5 lighting on a 20H with no co2 or excel. Distance to substrate is 13 ". I adjusted the height of the fixture up about 3" .. The fixture is a standard current 2 bulb fixture. The bulbs are close to the reflector and to each other which I'm sure is causing a decent amount of restrike. Using a Par meter I adjusted the height of the fixture to roughly duplicate the par readings of another non co2 tank with 2wpg of t8 lighting and standard aluminum reflectors.

    In your case if you have individual reflectors and if they are of good quality the amount of light can increase significantly. One of the problems using high output lighting on a non co2 tank is that the par readings at the substrate may be ok but the light intensity goes up dramatically as you take readings closer to the surface. Raising the lights decreases the difference between the light levels at the substrate and the surface.

    You have a deeper tank and better reflectors than my tank. I'm guessing the light levels may be ok with the lights sitting on top. You might raised them a bit depending on how the plants and algae look.

    If my memory serves my correctly a standard 29 gallon is 30" wide and a 24 watt
    t5 bulb is 24 inches wide. Raising lights will improve light spread.
     
  7. oldpunk

    oldpunk Guru Class Expert

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    no idea, i haven't figured it out yet. (probably Nymphaea zenkeri)

    Hoppy just posted this at TPT:

    [​IMG]

    you got awfully close. lol

    thanks a lot guys!
     
  8. Henry Hatch

    Henry Hatch Guru Class Expert

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    When I raised the lights on my tank I adjusted it so that I had about 40 micromols at the substrate and 80 at the surface. The center of the bulb at the surface has a little more. I thought 80 micromols was no more than low - medium light ? Hoppy's chart indicates 80 micromols is high light. Is this correct ? I realize there are no standards other than observation and experience that I could find to define light levels. So I have too much light ?
     
  9. trong

    trong Lifetime Charter Member
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    im assuming that this graph is for light at the surface of the water. is there such a graph for micromoles at different depths of water? i'm pretty sure that graph would be profoundly appreciated. this thread on light is in my opinion, mind blowingly important, and the most interesting in a while if it's correct. according to this graph i should have my lights on the roof of my house. (my attempt at humor)!i think i have to much light!
     
  10. Gerryd

    Gerryd Plant Guru Team
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    Hi trong,

    I seem to remember a GREAT series of posts by vaughn on this subject. I seem to remember he did some charting showing how the value changes with increase/decrease in height from the tank.

    Do a search and see if you can find them. Were in the last 3 months and should be easy to find :)

    Let me know and I will find them....

    Josh,

    I think you should raise them as high as possible to START and adjust downward. It is always easier to guage MORE growth as opposed to LESS growth IMO...LOL

    You are looking at using lots of low light plants (as noted above by others) and will not need much light at all. Most of us have much more light than we think, and I find that many plants need less than published.
     
  11. Biollante

    Biollante Lifetime Charter Member
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    Not Sure

    Hi Josh, Henry,

    I have to confess that most of what I know (think I know) about PAR lighting I have learned here from Hoppy, Tom Barr, a little on the internet and a bit from the local library. :)

    My experience with a PAR meter is limited, I’ve only had it a few weeks. Though I have forty tanks of various shapes and description and another 100 or so ‘tubs’ along with a number of ponds and a couple of ‘swimming pools’, full of weeds and fish. As far as I can tell by my unscientific walking around and sticking the meter into things and places, Hoppy’s charts, here and elsewhere are correct. ;) http://www.barrreport.com/showthread.php?t=6036

    I confess I was a bit, okay more than a bit skeptical when I first heard about these things. What can I say I was totally and utterly, not even in the ballpark, wrong? :eek:

    Yes, I find various Anubis and such growing happily at 27 or so umol. Places I had no idea I find plants growing happy and apparently healthy down around 20 umol, I have been cutting lighting back, I am trying to step it down in a few cases. It is starting to explain some of the success I have had with tanks in ambient light.

    The trick, the thing I am looking for is avoiding too much light at the surface or top 3 or 4 inches. One thing, the obvious thing is floating plants or floating leaves. The other I have been working with shade cloths using brighter or better reflectors and messing with the angle of incidence.

    Anyway, sorry, I get over exuberant. :)

    Biollante
     
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