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Discussion Starter · #1 ·
I'm having trouble understanding this:

Does the WPG rule work for NO fluorescents? I have a 20 watt NO tube and a 9 watt screw in PC both 5500K but the 9 watt puts out much more light than the 20? Does lumen/lux work into it or does it not apply because its only a measure of light intensity according to the human eye and not what fish need?

Thanks
 

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The WPG rule was actually based on T12 fluorescent tubes.

The problem you are having is due to the more compact source of light from the 9 watt bulb.

Also the CRI comes into play. Some really good plant bulbs appear a bit dim because they output light for plants and not human eyes.
 

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Discussion Starter · #3 ·
So if I have 2 tubes of NO, 20Watt each over my 15G, even though it LOOKS really really dim in there, I have enough lighting ?
 

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Maybe. Plants require a minimum level of intensity that is not reflected in the WPG rule.

Also you need the correct k values.
 

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I think the watts per gallon "rule" evolved from T12 bulbs, keeping the same number of 2 watts per gallon, but requiring that the watts be from PC bulbs in good reflectors, which is another way to increase the recommended amount of light. It is and always was a very rough guide to the light needed.
 
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