# A little confusion about lighting



## pambe1975 (May 27, 2009)

Ok, I get the watts per gallon and I know that there is more to lighting than that. I just recently added 2-21watt t5 10,000k bulbs along with 1-96watt compact florescent for my 50 gallon acrylic. Is the watts per gallon rule based on the number of watts + number of bulbs with that wattage? Needs some enlightenment on this subject. Thanks ahead of time.


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## pambe1975 (May 27, 2009)

let be a little more clear. How many watts/per gallon would I get from 2x21w actinic t5's and 1x96w compact florescent? would it be 2.34 wpg or 2.76, does it even matter since the difference is so small?


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## Newt (Apr 1, 2004)

Are the 2x21w actinic t5's high output? -These are saltwater bulbs and really dont do much for plants.

How many gallons are in the tank that are subjected to light? - not the tank size and not what is in the substrate and filter.


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## pambe1975 (May 27, 2009)

How would I determine actual gallons, do I go by weight? If I go by weight then I would say 40-43 gallons, but this is rough guesstimate


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## Newt (Apr 1, 2004)

Post the *inside* dimensions from the substrate to the surface and from glass wall to glass wall in both directions. I will calculate the gallons for you.


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## pambe1975 (May 27, 2009)

Will do, thanks for your help Newt


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## pambe1975 (May 27, 2009)

here are the dimensions:
Depth 15"
Length 39"
width 14"


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## Newt (Apr 1, 2004)

Based on those measurements you have 4.74 cu. ft of H2O which equals 35.46 gals.
This equates to 3.89wpg.
I didnt know if your 10,000K bulbs were high output or not. The 96 watt is T5 but not HO.
If your 10,000K is actinic it may not be doing anything for your plants. It could actually shutdown photosynthesis as infra-red light does. Actinic bulbs are designed to emit at a wavelength of 460nm which is beyond the action spectrum for plants as shown below.










I really dont understand how/why people began using saltwater bulbs in planted tanks. There are just so many better bulbs for plants. I'd change them out.


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## Seattle_Aquarist (Mar 7, 2008)

Hi pambe1975,

One of my aquariums is 36" X 12" X 21" to the substrate and I use one 96 watt 6700K compact fluorescent with an AH Supply reflector in a DIY enclosure. This amount of light allows me to grow just about any plant with the exception of high light requirement foreground plants. 

With the decreased depth of your aquarium, and based on the inverse square rule for light intensity, you will have slightly more than twice the light intensity of my tank at the substrate level if you run just the 96 watt bulb.


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## pambe1975 (May 27, 2009)

Thanks for the help!


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