Watts per gallon? - The Planted Tank Forum
 
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post #1 of 5 (permalink) Old 11-12-2006, 03:45 PM Thread Starter
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Watts per gallon?

Could someone please explain to me how watts per gallon works? I don't get it, it's not like light particles stay contained in the tank, it goes through the glass...
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post #2 of 5 (permalink) Old 11-12-2006, 03:51 PM
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Rex explains a better system than WPG here: Minimum Light Threshold...or am I nuts?

We just use WPG because it's easier math to do...and yes, the WPG "rule" isn't exact if you have poor reflectors, or bent tubes which increases re-strike. "True" WPG assumes 100% of the light from the bulb goes into the aquarium at pretty much a 90 degree angle...it's just a rough estimation.

What it also doesn't really take into account are hexagon/tall tanks that have 18"+ inches of depth. Light can penetrate only so far. If you have a a 5 gallon container 30" tall with a 50 watt light up top, I doubt you'll be able to grow anything near the substrate, etc...

I only use the WPG rule for standard tanks of at least 15 gallons up to about 90 or 100 gallons.

Last edited by epicfish; 11-12-2006 at 03:57 PM. Reason: Forgot some stuff.
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post #3 of 5 (permalink) Old 11-12-2006, 03:52 PM
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It's just a generalized rule of thumb kind of like the 1'' of fish per gallon rule, although that hardly applies to anything anymore. It's basically from what I can understand a way to ensure you have enough light penetration according to the size of tank. Say, while two of these bulbs would be enough to grow plants in a 55G they surely wouldn't be enough for decently larger 75G. So 20-30watts may be plenty enough for a 10G, it would hardly grow the easiest of plants in a 30G.

I dunno if this helps, it might not make any sense at all haha. All in all though it's not about containing the light, it's just about making sure you would have enough depending on the size tank.

One thing I've been wondering though is if WPG IS everything and how big of a role lumens play. I recently switched from T12 to T8 bulbs because I wasn't seeing much growth with the T12s now for me it went as follows

T12-40watt-1900 lumens
T8-32watt-2500 lumens

So, from what I gather is eventhough the T8 is lower wattage it produces more light, so would that mean better plant growth?

Also, it seems that the smaller a tank gets the less the WPG rule applies. Surely in a 1G tank you wouldn't be able to grow glosso with 3 watts total of light. I just last night put a 20watt bulb on my 5.5G but, Im not sure if even that will be enough to grow plants, guess I'll just have to see.


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post #4 of 5 (permalink) Old 11-12-2006, 04:00 PM
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Quote:
Originally Posted by HybridS130 View Post
One thing I've been wondering though is if WPG IS everything and how big of a role lumens play. I recently switched from T12 to T8 bulbs because I wasn't seeing much growth with the T12s now for me it went as follows

T12-40watt-1900 lumens
T8-32watt-2500 lumens

So, from what I gather is eventhough the T8 is lower wattage it produces more light, so would that mean better plant growth?
Minimum Light Threshold...or am I nuts?

Lux per square inch. =)
(1 lux = 1 lumen / sq. meter)
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post #5 of 5 (permalink) Old 11-12-2006, 04:35 PM
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Yeah I must've hit the reply button only seconds after you, hehe but, yeah I saw that after it refreshed.


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