Lighting an Aquarium with PAR instead of Watts - Page 16 - The Planted Tank Forum
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post #226 of 439 (permalink) Old 09-12-2013, 05:50 AM
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then why all are spendint the time wasting on the rubbish comments?
Care to elaborate? I believe the rubbish comments are the product of an active discussion...
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post #227 of 439 (permalink) Old 09-13-2013, 05:22 AM
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Hi All, need some quick help, planning to put 6 tubes of t5ho 80watts over 36 inches abaove substrates (tank height is 30 inches and the lowest i can go is 36 inches). Consider high lights? i need high lights please. Thanks in advance.
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post #228 of 439 (permalink) Old 09-13-2013, 09:14 PM Thread Starter
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You should get around 60-70 PAR with a 4 bulb AquaticLife T5HO light. A 6 bulb AquaticLife fixture should give about 50% more light. Either one would qualify as high light, as I see it.

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post #229 of 439 (permalink) Old 09-13-2013, 09:35 PM
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Originally Posted by gus6464 View Post
Ecosmart PAR38 18W 5000K



I would say 30" from sub would be the sweet spot for a medium-high light cube. I got this bulb for $10 at HD. Perfect cheap bulb for those 7.5g cubes.
Gus, missed this one.
Very useful info - ty!
Looks like a spotlight, pretty interesting narrow beam close up. Now, waiting for sale

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post #230 of 439 (permalink) Old 09-13-2013, 11:36 PM
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I notice there's a note about screen covers reducing PAR by 30%, what about if a plexiglass cover is between the light and the water (with light raised a bit above the cover and water)? How will this effect the PAR (if at all)?
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post #231 of 439 (permalink) Old 09-14-2013, 05:14 PM
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Quote:
Originally Posted by Hoppy View Post
You should get around 60-70 PAR with a 4 bulb AquaticLife T5HO light. A 6 bulb AquaticLife fixture should give about 50% more light. Either one would qualify as high light, as I see it.
Thanks hoppy. I got the 6 tubes in the end. Hehe.
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post #232 of 439 (permalink) Old 09-17-2013, 11:06 PM
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I have a 36" 40g bowfront I'd like to turn into a planted tank... Any decent t5 lighting fixtures that could get me into the low or medium light range that are under 150$?
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post #233 of 439 (permalink) Old 09-18-2013, 04:51 PM
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Hi everyone,
Has anyone done a PAR reading on ADA Aquasky? If so please can you direct me to that post.

Thanks in advance.
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post #234 of 439 (permalink) Old 09-19-2013, 05:43 AM
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ADA Aquasky PAR tested

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Originally Posted by saiko View Post
Hi everyone,
Has anyone done a PAR reading on ADA Aquasky? If so please can you direct me to that post.

Thanks in advance.

Mr. Aqua 30cm cube journal
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post #235 of 439 (permalink) Old 09-19-2013, 12:10 PM
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Thank you vvDO
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post #236 of 439 (permalink) Old 09-22-2013, 01:23 AM
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Hoppy – This whole tread is outstanding and really answers so many questions about lighting. I’m an older guy just getting back into the hobby and this talk of lighting is quite confusing.
I have graduated from the old T-12s and am now using T-8s, although T-5s and LEDs are probably the way to go – I’m sticking with the 32 watts T-8s (6500K) for right now. So here is my question for you. I have a 55 gal tank: 48”long x 12”wide x 18” from the bottom of the T-8 tube to the top of the substrate. It is a dirted tank, with the usual low to medium light plants. I just started using 2 shop type lights, each with 2 bulbs for a total of 4) T-8 bulbs. The box for one of the shop sets says: for 2 bulbs = 3100(x2) Lumens, Lumens per watt – 96.8, CRI 86, Ballast Factor Multiplier 0.93
The question is 4 bulbs too many? Are 2 bulbs not enough? All bulbs are 6500K Daylight. I don’t appear to be having excessive or any algae, my dwarf sag is finally growing and my jungle val is going nuts. Thanks for your time. - Chris

Last edited by Arkansas; 09-22-2013 at 03:48 AM. Reason: addition
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post #237 of 439 (permalink) Old 09-22-2013, 02:35 AM
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Hello,

I'm jumping in here a bit late, but reading the thread and the questions and difficulties that people are having are the product of a serious misunderstanding best encapsulated in the following statement:

Quote:
Originally Posted by Hoppy View Post
PAR isn't something that you put into the tank. It is the intensity of the light at various points in the tank.
PAR is something you can put into your tank. It is measured in microEinsteins which is a measure of the number of photons (these are real things!). What is being measured with PAR-meters, and what Hoppy is talking about is Photosynthetic Photon Flux (PPF), also called Phososynthetic Photon Flux Density (PPFD). This is measured in microEinsteins per square meter per second. So, to summate,
PAR = uE
PPF = uE/m2/s

From the data accumulated at http://www.apsa.co.za/board/index.php?topic=4454.0 (in 2010) it is calculated that, on average, you get about 1 PAR/W from tube/fluorescent lamps (T8 & T5). (T5s are only marginally better for output and this is due, mostly, to geometry.) So a 20 W CFL will put out as much PAR as a 20 W T8 tube (because the physics of light emission process is the same). Of course the CFL is all twisted and a lot of light is lost among the twists and turns of the tube (especially as about 30-40% of the light emitting surface is facing another light emitting surface and gets lost by "squishing"). PAR output of LEDs varies from 1.55 to 1.03 PAR/W (depending on bias current) but the geometry of the lamps greatly increases efficiency as the light in concentrated over a narrow beam focus. We suspect that LEDs are, in the end, 3 times more efficient than tube lamps based on the number of LED watts needed to get plants to pearl compared to T5 tubes.

Using this data, and Tom Barr's PPF data for actual planted aquariums and scientific journals for attenuation coefficients* we worked out the following: http://www.apsa.co.za/board/index.ph...9062#msg109062 (and have been fine tuning it since 2010 as we gathered more data). This is our best guess for how many watts you need over a tank to achieve 40 PPF at a certain depth.

The major factors (that will vary with each aquarium setup) are the turbidity of the water (the more light absorbing dissolved solids the more light is absorbed with depth), the amount of light lost to reflection due to surface disturbance or angle of lamp to water (90% of the light hitting the water at 60o is reflected and it gets worse the shallower the angle). You need the lamps as close to the water as possible to keep the angle of incidence steep. The quality of your reflector is also critical. With a bad reflector you are probably getting less than 50% of your light into the tank. With no reflector the value is closer to 30%. A model to determine reflector efficiency is available at http://www.apsa.co.za/board/index.ph...41393#msg41393 .

Essentially, if you can engineer a reflector with high efficiency and place it so that as much light as possible hits the water's surface of the tank, then you can, with some certainty, use W/m2 to estimate PPF at specific water depths.

So, to summate by example: if you have two 30 W T8 tubes they are emitting approximately 60 PAR. If you have a good reflector that can focus all the light into the tank (which is impossible but lets just pretend) which is 36 x 12 inches in surface area you will get 222 PPF (PPF = PAR/(0.9 x 0.3 m)). Assuming 70% of the light actually enters the water, this will mean you will have about 99 PPF at 15 inches of water depth (not tank depth). More than enough for Glosso and HM and unless you have ample CO2 and nutrients you will get an algae soup. Without reflecors the value would be closer to 30-40 PPF which attests to the old adage that 2 full length tubes are enough to grow just about any plant.

* The issue here is that light moving through water is subject to the law of attenuation, not the inverse square law, and there is significant internal reflection of the light moving from the water to the glass. Light out of a fishtank follows the inverse square law just fine meaning the higher your lamps above the tank the less your photon density becomes with distance from the source.

Tyrone
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post #238 of 439 (permalink) Old 09-22-2013, 04:22 AM
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Originally Posted by tyronegenade View Post

Using this data, and Tom Barr's PPF data for actual planted aquariums and scientific journals for attenuation coefficients*
The major factors (that will vary with each aquarium setup) are the turbidity of the water (the more light absorbing dissolved solids the more light is absorbed with depth), the amount of light lost to reflection due to surface disturbance or angle of lamp to water (90% of the light hitting the water at 60o is reflected and it gets worse the shallower the angle). You need the lamps as close to the water as possible to keep the angle of incidence steep.

* The issue here is that light moving through water is subject to the law of attenuation, not the inverse square law, and there is significant internal reflection of the light moving from the water to the glass. Light out of a fishtank follows the inverse square law just fine meaning the higher your lamps above the tank the less your photon density becomes with distance from the source.
I'm not following this.. Seems the inverse square law "applies" and you have an added component(s) as you have mentioned.. adsorption, scattering, refraction ect..

As for attenuation.. specific wavelengths are adsorbed at different depths BUT this is not realty applicable at what we are using (like 2 ft.)


for fun
http://scholarsarchive.library.orego...pdf?sequence=1

Last edited by jeffkrol; 09-22-2013 at 04:40 AM. Reason: fun added
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post #239 of 439 (permalink) Old 09-23-2013, 07:20 PM
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Jeff, that graph is very interesting as it would speak against my attenuation coefficients:
red = 1.007
orange = 0.755
yellow = 0.336
green = 0.226
blue = 0.132
violet = 0.216
These have been double checked against various sources and hold up well, especially in water rich in polyphenolics (like our fishtanks and very much unlike the open ocean). The article will make for good reading later on when I have the time...

As much as 50% of red light is lost in 2 foot of water. The attenuation coefficient for red light is 1.007. Do the math. In addition, visit the data I link to. A model of attenuation fits the data nearly perfectly, giving an R^2 of 0.999979*. The inverse square law doesn't fit at all.

*This good statistical fit doesn't necessarily mean that we are observing attenuation in a pure sense. I suspect that the reality is a combination of inverse square, internal reflection and attenuation. If this suspicion is correct then wider tanks should have higher attenuation coefficients than narrow tanks. I haven't had the chance to do the experiment and test this hypothesis. But, for now, the math works as if attenuation is the major factor.

I don't have the time to argue for my model. I suggest that people test it by experiment and then let me know where it is wrong. As an experimental scientist I don't need my theory to be correct, I just need it tested. I expect the assumptions and data used to arrive at the estimates to be revised but so far the attenuation model holds up to scrutiny and gives a very good estimate of how much light intensity is lost with depth. The major holes are for how much light actually gets into the water column, which has more to do with reflector design than anything else. The math I show on the other site is for a moderately efficient reflector design and most of the light actually entering the aquarium.

This is a simple model that can be used to guesstimate the amount of power you need over your aquarium and if it has failings they will quickly show in experiments where the model is put to the test.

Tyrone

Last edited by tyronegenade; 09-23-2013 at 07:51 PM. Reason: to be more polite
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post #240 of 439 (permalink) Old 09-23-2013, 08:56 PM
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Well to be perfectly honest, this is much more your field than mine.. So I give you a bit more that corresponds and also questions those findings..
http://www.cen.ulaval.ca/warwickvinc...Ffiles/137.pdf

Unfortunately it doesn't go far enough in red data..

You may want to start w/ this one..

to be clear, I'm certainly not saying your wrong and since you state:
Quote:
I suspect that the reality is a combination of inverse square, internal reflection and attenuation.
That pretty much puts us on the same page..

pay to play article:
http://link.springer.com/article/10....750-012-1084-2
http://link.springer.com/article/10....333-010-0207-5

I have no doubt that between the inverse square rule and attenuation you lose light, and specific bandwidths by depth....

This is probably the best.. go to pg 10.. Pretty close to your data.. except:
They throw in a red absorption by chlorophyll for the attenuation in red as a parameter..
http://www.serc.si.edu/labs/phytopla...s/DiagTool.pdf
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