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Hellos,

Got a 30g and just connected two 9w compact flourescent lights (Osram brand). The box says that the 9w compacts gives off light equivalent to 60w. So since I have 2 of these, I effectively have 120watts for a 4wpg rating.

By looking at the aquarium, it does not look like it is receiving 120 watts from the compacts.

Does anyone have any experience or figures on whether or not these wattages claims are accurate? Or does anyone know what is a 9watt compact equivalent to for purposes of determining wpg?

I also remember reading somewhere that higher lumens (brightness) does not necessary mean better lighting for plants. The article had an explanation as to what rating should is determinative of plant growth. However, I can't find the link. Anyone know about this?
 

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If it is the type of spiral bulb that I am thinking of, those two wattage numbers are expressing two different things.

The 9W is the actual amount of fluorescent power being drawn by the bulb, and thus the wattage number you should be using to calculate your watts per gallon. The second number is a comparison of the brightness of this bulb with the number of incandescent watts (watts from a normal light bulb) needed to generate this much light (60W normal bulb).

What you actually have is 18W of fluorescent light over your 30 gallon tank, so you are correct that is not receiving the amount of light you expected.

Hope that helps.
 

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HanShaSuro is right. You only have 18W. The 60W is the equivalent in incandescent. Besides that, if its the spiral bulbs, they only help for small aquariums (like under 10 gallons). They are designed for 360 lighting, and won't evenly spread it for your 30 gallon.
 
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