Watts per gallon

[African_Fever]

Ok, DoctorJ got me really thinking about this again, and it's something that I've been wondering about for a while.

I've got two screw in flourescents, I think each at 6 or 7 watts. This makes 14-16 watts total. Plants grow 100% better under this than 2 regular 15 or even 25 watt incandescents on a 20 gallon (according to normal belief it show grow better under the incandescent b/c of more watts per gallon). I know that the flourescents are equivalent to ~60 watt incandescents, but shouldn't there be some kind of conversion scale here or am I missing something? I've actually contemplated finding some incandescent fixtures and replacing my flourescents b/c in a standard 48" hood with two fixtures you'd have 4 bulbs, with an equivalent of 240 incandescent watts (if using 6/7 watt flours. = 60 watt incandescent, if you can find the 100 watt equivalents, that's 400 watts!!!), when a single bulb fixture in flourescents (what is used in 99% of them out there) may have a total of 40 watts. I know the spectrum is different and yada yada yada, but simple fact is all plants I've ever grown under the screw in flourescents grew like never before, with no CO2 or additives of any kind. I'm planning on building a hood for a newly acquired 120 and will definitely be including a number of incandescent fixtures along with the flourescents (you never know if I'll got crazy and try an Amano setup). If someone could enlighten me as to this, it would be much appreciated. I know the fish look different under both types of lights, but the plants grow so well under the screw in flourescents that it's hard to resist.

Thanks in advance for any enlightenment.

[AndyL]

This is going to get confusing fast... So many topics brought up - so many different directions I can go...

Ok, First off, the WPG "rule" is really a sh*ty rule in general, it works not so bad for the more common standard sizes (10,20,29,33,55) but outside that realm it really doesn't work. The WPG normally quoted - is based on flourescent lighting - not on the "Equivalent" rating of the incandescent bulbs.

Yes under two screw in compact flourescents at lower wattages - you'll grow plants way better than under incandescant. The reason why has nothing to do with wattage, or guideline conversion factors (ie 13w PC = 60 incandescant) it has to do with the PAR (Photosynthetic active radiation - the actual radiation emmited which feeds chlorophyl A) output of the bulbs. Any incandescant bulb has a very low PAR output - whereas by nature most flourescent tubes produce PAR quite effectively.

You will have trouble growing plants in your 120 (assuming it's the 24" depth version I'm thinking of) with PC or flourescent lighting... Water is very effective at filtering out PAR - and getting enough PAR to penetrate that depth will be a challenge. That's why you see most large planted tanks lit by metal halides.

Clear as mud?

Andy

[African_Fever]

Thanks Andy, actually it does make sense. The only plants I'll probably grow in the 120 will be crypts and vals, and I seem to be able to just about grow them in the dark (the crypts anyways).

Thanks again.

[ABwildrose]

I don't know where I read this or even if it is accurate, but I recall something about 1-2 watts per gal if using fluorescent lighting and 4-6 w/gal if using incandescent.

[AndyL]

I don't know where I read this or even if it is accurate, but I recall something about 1-2 watts per gal if using fluorescent lighting and 4-6 w/gal if using incandescent.

I don't know where you read it either - but it doesn't much apply... A 120g tank doesn't fit the standard wpg profile - and even going with 3wpg - 360w of flourescent light on it - isn't going to grow much more than low light plants.

Andy

[ABwildrose]

It probably isn't too accurate...I went looking through all my magazines to find it but I can't, but I do know I heard it somewhere. Anyways, it was only in relation to low light plants.