Lighting again

>> The phenomenon of total internal reflection occurs for the light
>> passing directly from the light bulbs to the inside glass surfac
>> aquarium.  This light gets entirely reflected back into the tank
>> it escapes the aquarium.
>> The reason you can read a book by the light of your (well-lit) t
>> whatever light strikes the plants, rocks, decorations, etc. insi
>> tank gets scattered randomly.  When this scattered light strikes
>> glass surfaces of your aqaurium, it is no longer at an angle sha
>> to provide total internal reflection.  It passes right out of yo
>> and lights up the room.
>In which case, unless I'm missing something,  it has left the
>tank, and ain't coming back.  Therefore it is, for all practical
>purposes lost to the system.  Which is exactly what I said.  In an
>EMPTY tank you might not lose any light, but in a PLANTED tank,
>you most certainly do.  And the deeper and more heavily planted
>(or otherwise decorated) the tank is, the more light you are going
>to lose.

Ummm, sure - but I don't think it's a question of losing "more" light.
Practically all of the light from the bulbs is going to eventually find
it's way out of the tank (no matter what's in there).  The only stuff that
"stays" is what the plants actually absorb in the process of
photosynthesis.  I can't make a comment about what percentage that is
(maybe some of  the experts can) but I'm guessing that it's small.  Most of
the light you provide to your tank eventually ends up lighting up the room.

The point I was trying to clarify is that the tank glass does trap some of
the original light from the bulbs (light that has not already scattered off
of plants, decorations, whatever) and send it back into the tank to be
(hopefully) used by some plants before being scattered back out of the

And I'm _not_ trying to argue that deeper tanks don't need more light -
sure they do.  No matter how you slice it, the farther away from the light
you get, the less intense it is...

        |    |
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    {  ,.      *     %
     `/  \        ,/'       Steve Robertson, GSRA
          ~\    ,/        UofM Radiation Laboratory
            @, /   http://www-personal.engin.umich.edu/~svr/