# CFL and watts per gallon question...



## chicken (Aug 22, 2007)

You go by the actual wattage, not the wattage of the incandescent bulb it is supposed to be equivalent to. 

However. . . watts per gallon is not really a very accurate measure of light intensity on an aquarium. This guideline sort of worked back when everyone was using T-8 and T-12 fluorescents. However, it didn't work on large tanks, or tanks as small as 10 gallons. And it works even less well once you get into cfl, pc, or t-5 lighting. 

If it helps you at all, I have two 13 watt cfls on a 10 gallon, and find it works well enough to grow some plants.


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## fermentedhiker (Oct 28, 2011)

With CFL's you don't use watts per gallon at all(even if it was a useful number), because increasing the number of bulbs doesn't change the amount of light received by a plant. Each bulb lights it's own area the same. You add more bulbs to cover more area, not to increase intensity.

I concur with chicken's statement though. Two 13watt CFL's work quite nicely on a 10 gallon.


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## talontsiawd (Oct 19, 2008)

As said, you can't really do watts per gallon with CFL's (not that it's a great way to do it anyway, especially on small tanks) because of issues with restrike and bulb positioning, and probably some other things I don't know about.

If you were to do it, you would compare it's actual wattage though as the watts per gallon rule goes of florescent bulbs (T8/T12) and a CFL is florescent. The "equivlant" is to an incandescent bulb which is not used on a planted tank often. So at 13 watts, it's equivalent to 13 watts of florescent, minus it's draw backs.

I agree with both people above. I used 13 watt bulbs in my old 10 gallons all the time, was great. Had issues with more wattage.


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## samamorgan (Dec 31, 2011)

h0meless said:


> As far as CFL goes, do you base the watts/gallon off of the actual bulb, or it's equivalent. For example, if I have a 13w CF bulb that is rated as an equivalent to a "26w bulb" or whatever, is it still classified as 1.3watts/gallon if this was the only light used on a 10gallon tank?


http://www.plantedtank.net/forums/lighting/168930-watts-per-gallon.html


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## h0meless (Jul 17, 2010)

Good deal. I recall reading a while back that the wpg wasn't much of an indicator for good plant growth, where as the spectrum of the lighting was really the main factor; however I was mostly concerned about it's effect on algae. I have 2 14w CFL bulbs over a 20h, and I can't seem to get rid of spot algae despite dosing with excel and frequent waterchanges =/


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## samamorgan (Dec 31, 2011)

PAR is the main factor, spectrum is a secondary concern. You can do several things here. Raise your lights to lower intensity, recheck your parameters for fert dosing and be sure it's all balanced, or up the Co2 to balance out demands. Algae issues aren't really a sign of too much light unless it's WAY too much, it's usually a sign of a requirement you aren't fulfilling.


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## jimclassic (Dec 14, 2017)

fermentedhiker said:


> With CFL's you don't use watts per gallon at all(even if it was a useful number), because increasing the number of bulbs doesn't change the amount of light received by a plant. Each bulb lights it's own area the same. You add more bulbs to cover more area, not to increase intensity.
> 
> I concur with chicken's statement though. Two 13watt CFL's work quite nicely on a 10 gallon.


Considering a tank of 24x12x18 inch, how much CFL and of how much watt would be required??

Thanks in Advance
Jim


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## fermentedhiker (Oct 28, 2011)

jimclassic said:


> Considering a tank of 24x12x18 inch, how much CFL and of how much watt would be required??
> 
> Thanks in Advance
> Jim


I would two would still work if you're using those hardware store clip on style reflectors. They are about 8.5" across. That way each bulb/reflector would cover a 12x12 area.

As far as the size of bulb to you? That depends on your setup and what you plan to grow. Here's an article that might give some insight that helps make a decision.

http://www.plantedtank.net/forums/1...al-power-saver-bulbs-lighting-question-2.html

The second page of that thread has some PAR test results using various bulbs.


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