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Thread: Lighting depth and PAR

  1. #1
    Join Date
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    Lighting depth and PAR

    Hi guys

    One for the lighting gurus.
    My tank is over 24"high so my water depth to substrate is around 28".

    My lighting is a mix of 2 54w t5 and a 24x3w Cree LED fixture which is 48" long and the led's run in line.

    These sit @ 30" from substrate (2" above water level)

    I know that Tom used to run 4 54w t5 @ 1m above substrate in a 24" deep tank fine. I was wondering though if water depth would reduce the par levels too much.

    There's a myth here in oz that tanks over 24" deep will need more intense lighting like in the form of halides or high output LED's

    Is this true?

    Sam

  2. #2
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    Don't underestimate that Cree led light. A single 60w Cree light on a 90 gal tank will give 30 to 40 par.

    So depending on how much light you want, you may have too much



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  3. #3
    There's the light spread.............issue with LED's vs say MH's and T5, PC, T8's etc..........while bright, over that small area......they do not spread unless the design of the entire array is well thought out/considered.

  4. #4
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    Thanks guys, that helps.

    So the intensity would be fine directly under the light but spread is the issue.

    I was thinking that so i added a single 54w t5 over each side of the LED to extend the spread in theory. I've been thinking that light is on the low low side @ the substrate because plants like ludwigia ovalis are pretty green and only 6" tall.

    I was also wondering if the PAR reading would be higher @ the base of a 24" aquarium with no water than a 24" aquarium full.

    I'm not familiar with how PAR works?

    I know a few guys use the LED units that i have but use 2 or 3 to even the spread so i'm hoping i can do so with using t5's.

    A PAR meter would be really helpful, does anyone know how much PAR a single 54w t5 would put out @ 28" ?

    Sam

  5. #5
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    Depending on the lens of the unit on the led it can spread as far as 18 inches. I know because we sell a unit like that. If you have a 90 or 75 g tank which is 18 deep I would only use the led and 1 t5. Unless you are going the high light high demand tank with co2 and ei and weekly w/c




    Henry Tomassini
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    "If it ain't broke, Fix it!
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  6. #6
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    Hi Henry

    The tank is 48" x 24" x 28" L x W x D.

    The led unit is a 1200 mm vertex illumilux
    Which is a total of 24x 3 w Cree xpe LEDs in a series. It hasnt got individual reflectors on it.

    Hope that helps I do run co2 and ei fertz etc.

  7. #7
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    Quote Originally Posted by samh View Post
    I was also wondering if the PAR reading would be higher @ the base of a 24" aquarium with no water than a 24" aquarium full.

    I'm not familiar with how PAR works?

    A PAR meter would be really helpful, does anyone know how much PAR a single 54w t5 would put out @ 28" ?

    Sam
    Can anyone shed any light on this for me? Pardon the pun

  8. #8
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    Quote Originally Posted by samh View Post
    Can anyone shed any light on this for me? Pardon the pun
    Hi Samh,

    PAR is simply a unit of measure that is applicable across ALL types of lights, T5, T8, CF, MH, LED, etc....

    http://en.wikipedia.org/wiki/Photosy...tive_radiation

    PAR readings should always be taken with the tank full of water and the meter sensor under the water...

    There are PAR charts available that show average PAR for various types of lighting...

    http://www.plantedtank.net/forums/li...5ho-light.html

    I used T8 on my 24" tall 180 for a long time but I was not aiming for a high light tank either..

    A way to look at tanks in terms of light using PAR measured at the substrate:

    Low light - up to 30-35 micromoles
    Med light - 35-75 micromoles
    High light > 75 micromoles

    So, the use of a PAR meter tells exactly how much light the PLANTS are getting...

    I hope this helps a bit.
    Last edited by Gerryd; 02-20-2012 at 01:46 AM.
    Thanks,

    Gerry.

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