# T5 light output vs. wattage



## treemaker (Mar 5, 2006)

I have been researching lighting for my 29 Gallon and arrived on a double strip T5 fixture with 2x18 watt T5 bulbs. The fictures are so small that if I want I can add another. 

My question is regarding the watts/gallon rule of thumb I am seeing on almost every aquatic plant website. Aren't Watts simply a measure of power consumption rather than nominal light output?? If so, wouldn't it stand to reason that a more efficient bulb (ie T5) that produces less heat be focusing more of that consumption on producing light?? The frustration for me is that I have yet to find actual lumen outputs for any of these bulbs to compare.

If I had to guess I would think that a measure of light output would be far more useful. Anyone else wondering about this??

Thanks


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## gnatster (Mar 6, 2004)

There has been a fair amount of discussion about this very topic. WPG is a decent basic rule of thumb thats easy to figure while standing in the LFS contemplating that new tank. 

Lumens per sq unit such as inch or cm and then compensating for depth would be a far better method. 

The devil is in the details. Not all bulb makers make it easy to find the lumen rating. Spectrum and CRI should also be figured in and lets not forget the efficiency of the reflector material and design. Lets not forget that different ballasts also change the bulbs output slightly. 

We can get as complex as we want to be and I find the subject fascinating.


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## treemaker (Mar 5, 2006)

Thanks...glad to hear it is not just me.

I spend a lot of time at work measuring light intensity etc., and I have always focused on light intensity rather than power consumption. Very interesting topic for sure. I guess my plants will ultimately tell me if I have enough light, but I think I am going to try to measure it myself just for the sake of interest.


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## gnatster (Mar 6, 2004)

You can find some good articles here on the science behind measurements for aquarium lighting.


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## Laith (Sep 4, 2004)

Using wpg as a basic rule of thumb says that you will have around 1.2wpg of light with that fixture. Yes, T5s are more efficient etc but the wpg gives a good enough general idea of the lighting, at least in the area of planted tanks.

So therefore you will have a low light setup... 

And welcome to APC!


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## treemaker (Mar 5, 2006)

Thanks for the replies. Right now all I really have are a few Java ferns and a couple Vallisneria (oddly, the Vals are doing quite well but maybe they will run out of gas soon). The fixtures I am looking at are so small that I could easily fit 4 of them across if I really felt the need, so I think I will take it 1 at a time. 

Cheers


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