LIghting and other Sorrows

YES, I did measure the light intensity, as several folks have asked. So has a
Licensed Professional Engineer friend of mine, preparing evidence for a court
case. (The case had NOTHING in the world to do with our aquarium lighting,
but he was comparing theory to practice in another case with practical
similarities to our lighting problems.)  In the real world of our tanks, the
Law of Inverse Squares works pretty darned well.  It is NOT a perfect
relationship, because we are NOT working with a point source of light.  It
is, however close enough to help us a great deal with our lighting problems.
 Yes, parabolic reflectors help. Mirror reflectors also help.  What we are
trying to do is get enough light at the right place at the lowest original
cost and lowest operating cost. 

The difficulty we generally have is with the sensitivity of the human eye.
 Our eyes are designed (Or, perhaps have evolved?  :-)  ) to work at some
dramatically different intensities of the spectrum called "visible light."
 If you sincerely feel that the Law of Inverse Squares does NOT apply at all,
I suggest you try having a friend hold a 15 watt fluorescent bulb exactly 12
inches from your eye, then move it quickly to only 2 inches from your eye.
 Have the friend look at the pupil of your eye at the same time.  You can see
a dramatic increase in light intensity, but you can be pretty sure your eyes
will NOT tell you that it is "36 times as bright."  Sometimes you can believe
your eyes, sometimes you can NOT believe your eyes.

I did not bring this up to cause problems or cause any hurt feelings or put
anybody down in any way.  "Men of good will can disagree." 

A really easy way to check out lighting intensity - crude, but still useful -
is to use a camera with a built in light meter.  Every "f stop" is a
doubling, or halving, of the light. You can do this from OUTSIDE the tank!
 (I can just see someone lying on their back at the bottom of a BIG tank,
aiming a camera at the surface!!  Actually, that is not as silly as it might
sound.  Try this with a camera in an underwater housing, in a swimming pool.
Yes, you may have to keep a sharp eye out for people with white coats and a
great big net!  :-)  )

The bottom line I was working on was the relationship of light source
positioning as it affects the light in the tanks.  The closer to the water
surface, the better.  There are no miracle reflectors, there are no miracle
lights, there is no free lunch. I wish I could show you the practical results
of this as it applies here in the Aquarium Center.  It is extremely close to
the numbers I gave, i.e. two and a half times brighter at the gravel surface.
That is why I rounded off the figures.

Not trying to give anyone a hard time, just trying to be helpful.