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This refrences my previous question I asked about Building a DIY light fixture with screw in compact fluorescent lights. My original question was posted in the planted aquarium forum yesterday. I thought I got it, but after reading the thread Frank recommended (thanks Frank for your help), I think I got it backwords. The thread was discussing the use of helical screw in fluorescents and whether to use the the lower # (power consumed ie. 26 watts) or the higher # (equivalent incandescent output ie. 100 watts). The final conclusion was to use the higher number in this thread. The original watts/gallon numbers were based on incandescent lighting, not fluorescent. So if I want approx. 200 watts over my 75 gallon tank, I should be able to use 4 13 watt compact fluorescents with a rating of 60 watts each for total of 240 watts. Did I interpret the thread correctly ?

Hi,
Yes.
The bulbs are rated at the equivalent light output of
a 60 watt bulb but only consume 26 watts.

If you can find the bulb rating in Lumens then you would
have an even better picture of what the total output would
be. But using the watts per gallon idea you have it.

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

I've always been told and seen the wpg rule based on fluorescent wattages with 1wpg of fluorescent light being the minimum for growing plants and up to 2wpg of fluorescent still considered low light. Irregardless of what the wpg rules were originally based on this is what appears to be generally accepted today.

Compact fluorescents do put out more light than NO(normal output) fluorescents and so you might get away with growing some low light plants in a 75g with (4) 13w pc bulbs but this is going to be considered very low light. The 1wpg and under range not the over 3wpg that you would have if you used the incandescent equivalent. It's pretty obvious that doesn't work since 52w of pc light is not going to grow much on a 75g so the rule wouldn't fit if you used incandescent equivalents. I put (4) 65w pc bulbs on my 55g before I considered it high light. That's 260w or 4.7wpg of compact fluorescent light. That's like 1200watts of incandescent or 21wpg on a 55g. Doesn't work. Go off the fluorescent values not the incandescent equivalents.

http://forum.aquatic-gardeners.org/viewtopic.php?p=4689&sid=0359fc227ab597131f001ef840d81e36

Frank


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--

My experience from trials on my own tank are that wattages are only a small part of the story light spectrum is the most important

Choose the right plants and you will be fine
I have only 30 watts on a 40 gallon and have no problems growing ludwiga, 2 types of swords and ambulia. I initially had a tube at 6500k and it did yellow a bit but switched to a 18000k powerglow after recommendation from my LFS and have been having to prune my plants ever since

Nobody uses incandescent lights on planted tanks. So watts per gallon when you hear people referring to it for planted tanks refers to florescent watts. I have two 13w screw in bulbs on my 10g tank giving me a little over 2 watts per gallon. If I were to go with incandesent equivalants of 60 watts each, that would mean that I have 12 watts per gallon on that tank.

The only reason they provide the incandescent equivalents on those bulbs is because most people are buying them to replace incandescent bulbs, if they only advertised them as 13 watts nobody would buy them. Watts is just a way of calculating how much power they use, it is not a measure of light. That's why they can boast of being more power efficient, 13 watts is less power than 60 watts. If you leave a 60 watt bulb on for an hour, it consumes .6 kilowatt hours (this is how the power company charges you for electricity if you look at your electrical meter or your power bill). This has nothing to do with measuring light output, but if you are comparing florescent bulbs to florescent bulbs, obviously more power consumption = more light. Comparing florescent bulb wattage with some other type of bulb wattage is only telling you how much power each will consume, nothing about how much light they will be putting out since different types of bulbs use energy differently.

Four 13 watt compact florescents will not be enough light on a 75 gallon tank to plant much of anything, maybe low light plants will live. I have two of these on my 10g and it's just basically keeping my plants happy, it's not super bright by any means.