# Background/Substrate Color: A Theory



## Hawkian (Apr 14, 2010)

The experience of replacing the reflectors on the 10G and setting up a completely different tank than the one I already had has got me thinking about light reflection inside a tank. Anyone who is running a planted tank has to take light requirements into account at some time or another and we are constantly worrying about not enough light or too much light, etc. What follows is not a revelation by any means but it’s a theory I have that I thought I’d share. 

Here are my two tanks:










The 32G (on the left) is lit by two T8 bulbs at 20w each. By the old WPG standard, this gives it 1.25 WPG, which equates to low light. The 10G is lit by two CF bulbs at 10w each. Again by the old WPG standard, this gives it 2 WPG, which is medium light. I think it’s pretty clear from the picture that the 10G has better lighting than the 32G. There are two other factors that also contribute to making the light brighter in the 10G in my opinion.

*The Substrate*

The substrate in the 32G is GeoSystem Black Beach Gravel, which is more grayish than black. When I initially started the tank two years ago I wanted a dark substrate thinking it would help display the fish colors better so I bought the darkest substrate I could find in the store. If they’d had black then I would have bought that. The substrate in the 10G is play sand. When I setup the tank a few weeks ago I was going for cheap and I had a bunch of play sand leftover from building my son’s sandbox last year so I decided to use that. The two substrates are very different in texture but also in color. The sand being a very pale color, will tend to reflect light back into the tank more than the black beach gravel, giving the 10G a look of a brighter light intensity.

*The Background*

The 32G initially had an all-black background and it was later replaced with a dark planted look background. I initially placed a black background on the 10G also, again thinking that it would make the fish colors show better. After filling the tank I realized that I essentially had setup a miniature of my 32G so I changed the background around (the commercial ones usually have two sides that can be used) and put an almost all-white background on the tank. Now there are arguments to be made about what backgrounds are nicer (to this day I’m not wild about the white background) but I’m convinced that a lighter color substrate and background helps propagate the light better in the aquarium, which is likely good for the plants.

As I said on opening this isn't a revelation of any kind but looking at my two tanks last night I realized that the 10G looked brighter in part because it has better lights but also because it has a lighter-colored environment. If you took two 6 X 6 wood boards and painted one black and the other white, and laid them out to look at in the bright summer sun, you'd have no problems looking at the black one but you'd probably have to squint your eyes when looking at the white one because the light is being reflected. Ever tried walking on snow on a bright sunny winter day? You'd need sunglasses because the snow reflects the light. I think the same principle applies to the aquarium.

I just wish I had thought about it last year when I was trying so hard to get better lighting in my 32G. All I could think about was the lights themselves... never thought about the environment.

Anyway that's my rant for the day.


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## Hawkian (Apr 14, 2010)

So I redid my 32G with a lighter-colored substrate (sand instead of dark gravel) and removed the dark green background from it. The tank is cloudy in the first pic but it is definitely looking like there's more light in there even though it's still using the same bulbs. I wish I had a PAR meter to test the theory... Here are the two tanks after the change, as well as before and after pics...


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## Hoppy (Dec 24, 2005)

How about a simple explanation? CFL bulbs are much brighter than T8 bulbs. You get more PAR from CFL bulbs at a given wattage than from T8 bulbs. That makes the one tank more brightly lit than the other. Light reflected from a light colored substrate would light the fish better, but not the plants. The light reflected off the glass back of the tank is the same for light or dark backgrounds, since the light is being reflected from the glass to air interface, not from what is behind the glass. If the glass is painted any color, no light is reflected by the glass to air interface, since there isn't a glass to air interface.


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