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Light Balance

Discussion in 'Lighting' started by AgMa, Aug 18, 2018.

  1. AgMa

    AgMa Junior Poster

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    Hi,
    I'm trying to adjust my light but without a par meter I find it quite difficult.
    So my tank is 22" x 14" x 18" (height) and I'm currently running a 3bulb T5 combo, front to back:
    Sera daylight brilliant 6500k (24w 1200 lumen)
    Sylvania grolux, aka flora type, pinkish (24w ~400 lumen)
    Juwel day 8000k (24w 1200 lumen)
    Unfortunately due to these strange dimensions, there is not big variety of bulbs, so I'm limited to 17" bulbs.
    Every bulb has juwel hiflex reflector which suppose it's great and the bulbs are 2.5" above surface.
    Do you think this is high light? Do I have to decrease it somehow?
    Fyi I can't lift it as there is a wooden canopy.
    I have pressurized co2. Ph readings:
    6.2 and 7.6 degassed.
    According to rotalabutterfly, I have ~180 par @ depth which makes me think it's not right because there are 24w bulbs at 17" and 21" too. Also the flora one, can't be calculated like 6500k, it's not powerful.
    What's your thought guys?
     
    #1 AgMa, Aug 18, 2018
    Last edited: Aug 18, 2018
  2. AgMa

    AgMa Junior Poster

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  3. tiger15

    tiger15 Member

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    You can buy a lux meter such as this to estimate how much light you have. It’s a lot cheaper than a par meter. There are factors to convert lux to par.

    https://www.ebay.com/itm/Digital-LCD-200-000-Lux-FC-Light-Meter-Luminometer-Photometer-Luxmeter-Tester/362042503817?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649.

    The sensor is not submersible, so you have to test it dry by lowering the water level. Its not a direct measurement of par, but it is better than any other estimates short of buying an expensive par meter. I have one and like it.
     
  4. AgMa

    AgMa Junior Poster

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    I don't think this method is reliable. Reading par under water, is a lot different than on air.
    I think I will buy the sq-120 sensor and connect it with a multi meter.
     
  5. tiger15

    tiger15 Member

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    Certainly, a PAR meter with a submersible sensor will be most accurate. But do you need that level of accuracy to justify a $150 - $300 PAR meter versus a $15 LUX meter to give you ball part figures? A cheap LUX meter is good enough for me to compare light intensity of different sources and to map out intensity variation by depth and location.

    There are many studies that derived conversion factors from LUX to PAR for difference light sources in air. HOP has conducted studies and found that submergence increased PAR values by reflection and refraction and I don’t remember the magnification factors he came up with,
     
  6. jeffkrol

    jeffkrol New Member

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    SQ-120 horribly under samples red below 650nm...........which will be a problem w/ the gro-lux tube.
    Then again it over-samples "higher" red so somewhat of a wash I guess.

    Reading PAR underwater is different but not "a lot" different.. Free air measurements will easily put you in the ballpark..
    Sq-520 is really the "best" as to accuracy and price..

    As to the SQ-120.. better off getting the Seneye.. about the same accuracy and same errors.
    do need windows tablet/laptop to make it "mobile" though..
     
  7. rajkm

    rajkm Article Editor
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    I don’t see a need for par meter. Not every hobbist has par meter.
    When in doubt start with lower light.
    I understand with T5 since there is no dimmer it’s harder but you can reduce number of bulbs or tails the fixture.

    When you think you have got your tank well balanced raise light slowly if you think you need more light, but do so in stages and over months.
     
  8. tiger15

    tiger15 Member

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    True, there is no need but a luxury to own a PAR meter. "Not every hobbyist has a PAR meter" is an over statement. I would say 99% of the hobbyists don't own a PAR meter.

    It's hard to justify buying a $200+ PAR meter that can do without to grow plants. But I bought a $15 LUX meter as a poor man PAR meter and learned a lot using it.

    I learned that the light intensity variation inside my tank can be substantial over a small distance, near the edge or center of my tank, or over shadowed by tank ornaments.

    I learned that brightness drops off quickly by distance from artificial light following the inverse square distance law.

    I learned that sunlight intensity does not drop off by inverse square distance law as sunlight intensity at the window and 20 ft away is identical.

    I learned that bright shade at the window or outdoor is stronger than high artificial light.

    I learned that the window glass and tank glass top cut off light substantially.

    I learned that my eye perception of brightness is deceptive, as the brightest indoor light is dimer than bright outdoor shade.

    I learned a lot about my household lights that I didn't know before regarding brightness, intensity variation, and bulb age factor.

    An imperfect measurement of PAR is better than none, and I think every hobbyist should own a cheap LUX meter as owning a pH test kit.
     
  9. rajkm

    rajkm Article Editor
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    I actually would say no.. many of these facts are know and mentioned in many places. You do t need to relearn that unless it’s for educational purposes, in which case I will encourage you to do so.
    Par meter and lux meter are also very different and there is no direct correlation because one is measuring brightness v/s other is measuring photosynthetic action. You should read up some debates on Facebook high tech planted tank group between Cara wade and others. (Cara is the authority on light in the hobby having been part of BML)

    As it pertains to tank, the known things of PAR are,
    It’s highest at below dead center of the fixture and reduces as you outwards in any direction and falls drastically the further you go.
    Red light does not penetrate as deep as blue.
    Actually what we measure is not PAR but umol
    PAR measured open sit vs under water in tank is different because of reflective light.

    KISS is the principal I recommend many new comers. Start with light that many others have measured and recommend. Should be dimmable or capable of raising and lowering.
    Learn to read plants and what makes them happy. Concentrate more on CO2 than anything else.
    Good husbandry is next most important thing.

    I have never owned a par meter or lux meter and probably never will. All I know is based on other people’s readings I am probably running close to 100+ and that more than sufficient
    New comers should not target anything more than 30-40 at substrate and that can be based off approximate values from other people’s readings.

    PS. Sunlight variations over miles is so minimal that you can’t even read. It like measuring par or lux at top of a tennis ball below a par 30 light placed 12” away.
     
  10. tiger15

    tiger15 Member

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    For only $15, I can’t understand why owning a LUX meter can hurt. It’s an educational tool despite the imprecision and imperfect correlation with PAR. Even PAR is imperfect as there is a better measurement called PUR (photo useable radiation). The LUX meter did not change my original estimate of my PAR level based on various empirical methods, just verified that my original estimate is in the right ball part.

    The reason sunlight does not drop off following the inverse square distance law is geometry, because sunlight beams are perfectly parallel within the scale of planet earth. But there are measurable and sometime severe reduction in sunlight intensity in the atmosphere due to particulate matter (PM) pollution.
     
  11. Phishless

    Phishless Lifetime Member
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    Cara Wade has presented a lot of great factual data regarding light in a planted tank.
    Does presenting factual data make someone "the authority", I'm not so sure?
    Debate on a web related platform usually means arguments and bashing of others, some don't accept the facts!

    $15 WTH, there's an app for that!
    I've tested 5-6 phone apps for lux, lumens, and foot-candles.
    Any form of measurement is better than none.
    Many have posted conversions to get to your approximate PAR and they are damn close!
     
    Greggz likes this.
  12. tiger15

    tiger15 Member

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    If it is free with cell phone, it's even better. I bet that since cell phone camera quality is so high today, its light sensor is likely of high quality too. One advantage of my cheap LUX meter is that there is no concern for dropping my expensive cell phone into water, and as the sensor comes at the end of a recoilable cable, I can take data at tight space.
     
  13. Phishless

    Phishless Lifetime Member
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    Test in open air only.
    Use multiplier for in water, which actually goes up a bit.
     
  14. tiger15

    tiger15 Member

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    Yes, I understand. I should re phrase as “dropping the cell phone accidentally in water”. I did it in air too during WC when the water level was drained down to few inches from the bottom. I snake the sensor around to measure light shadowed by obstacles, but It won’t be the same measuring it wet with standing plants. But ball part figures is enough, who need for precision.
     
    Phishless likes this.
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