How much light is this really? Compact Fluorescent question.

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Pombe

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Feb 4, 2005
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I've got a 20 gallon tank that used to have 2x15 watt incandecent bulbs which I recently switched out for two 9 watt compact floursecent spiral bulbs as I wanted to start growing some plants. The package says that these 9 watt bulbs are the equivalent of a 40 watt incandecent meaning I've got 80 watts or 4 watts per gallon over my tank right now.:confused: I mean it looks bright, but not that bright. Is there something I'm missing here?

Am I going to run into some big problems with this setup? I just want some greenery, not necessarily heavy fertilization and CO2 injection etc.
 
very good question.. I have the same one myself, having switched from incandescent to compact fluorescent in my 10 and both my 5 gallons.. someone told me that the wattage was counted the same in both the incandescent and fluorescent but for sure the tanks are much, much brighter.. I'd like to know the truth of the matter too..

I am going into the second month with these lights and the plants are doing well.. there is some algae but not too much for the oto and the platy to take care of.. I have two 14 watt in both my 5s and my 10.. I don't think you will run into much of a problem in your 20.. but if you get algae, try nerite snails if you can get them, they are amazing algae eaters.
 
When planted tank folks talk about Watts Per Gallon, they're talking about watts of Normal Output fluorescent lighting. Incandescent lights are much less efficient than fluorescent. Compact Fluorescent is a bit more efficient. Things like strikeback and reflector quality also have an impact.

If you have 2 9w CFs over a 20g, you have a bit less than 1 wpg or a low light setup.
 
carpguy said:
When planted tank folks talk about Watts Per Gallon, they're talking about watts of Normal Output fluorescent lighting. Incandescent lights are much less efficient than fluorescent. Compact Fluorescent is a bit more efficient. Things like strikeback and reflector quality also have an impact.

If you have 2 9w CFs over a 20g, you have a bit less than 1 wpg or a low light setup.
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Something is missing from this equation... how can the CF lights that I have put out less watts per gallon than the incandecent bulbs but still be brighter? If this is all compaired to light output of incandescent bulbs then this doesnt make sense.
 
Pombe said:
Something is missing from this equation... how can the CF lights that I have put out less watts per gallon than the incandecent bulbs but still be brighter? If this is all compaired to light output of incandescent bulbs then this doesnt make sense.
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9w of florescent lights are brighter than 15 watts of incandescent. But Watts Per Gallon is based on florescent lights in the first place. You do have better light now but you still only have a fairly low level. As I guide you have about 1w/g.
 
Pombe said:
how can the CF lights that I have put out less watts per gallon than the incandecent bulbs but still be brighter? If this is all compaired to light output of incandescent bulbs then this doesnt make sense.
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Its not compared to the output of an incandescent, its compared to the output of a NO fluorescent.

Your old incandescents put out the equivalent of less than 7 watts of the CFs you replaced them with, they just used 30 watts to do it. Since you now have 18w CF, the tank is quite a bit brighter. Its still only about 1 wpg of NO fluorescent equivalent.

It should be fine as a low light setup. Might be a little too low. Try some low light plants and adjust as needed.
 
carpguy said:
Its not compared to the output of an incandescent, its compared to the output of a NO fluorescent.

Your old incandescents put out the equivalent of less than 7 watts of the CFs you replaced them with, they just used 30 watts to do it. Since you now have 18w CF, the tank is quite a bit brighter. Its still only about 1 wpg of NO fluorescent equivalent.

It should be fine as a low light setup. Might be a little too low. Try some low light plants and adjust as needed.
Click to expand...

Ah. that makes a little more sense now... so go by the wattage of the CFs. Well, that means that my lights are a little dimmer than I want them to be. I guess I'll make another trip to Walmart and get some that are a bit stronger. I've got a couple of Crypts that will appreciate it...

thanks for the enlightenment! :p
 
I use CF spirals over two of my tanks. RTR pointed out something to me - due to their shape, you lose more light from spirals then from straight tubes. 18W CF is pretty low for a 20g, the WPG rule really starts to fall apart with smaller tanks. If you can find 13W or 15W bulbs that will fit the fixture (TMK, 13W are available the same diameter, just a bit longer than 9W) it will give you a little more light. The K rating of the bulbs is also important to consider - regular 'warm white' coloured bulbs aren't the best for plants, they're around 2300K. Plants will do best with bulbs between 5000K and 10000K. I've found several types of 'daylight' bulbs that are in that range, and the colour is quite nice (details in my sig. link if you're curious).
 
I picked up a couple of versions of higher wattage bulbs from walmart to try out. The 13 watt ones will fit into the Hagen light strip that I have, but I would need to McGuiver the strip a little bit to get the larger ones to fit as they are a larger diameter. Hopefully these won't generate too much heat...
 
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