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Re: light intensity

IDMiamiBob at aol_com wrote:

> >  I'm not sure that aquarium lighting falls off with the square of the
> >  distance,
> >  because there is quite a bit of internal reflection of the lights off
> >  the sides of
> >  the aquarium.  It may be something like depth^1.5, but I really don't
> >  know.
> A lot of light is absorbed by the water itself.  Perhaps not enough to be
> noticed, but it gets bluer fairly quickly.  I haven't really considered that
> before, but maybe a lot of extra blue would be better in tanks over 18".  Or
> maybe more red in order to compensate for the loss at the red end?  I don't

This is a good point. But how much blue/red is tricky. It all depends on
the amount of organics, and this is pretty hard to quantify without some
actual spectrophotometric measurements.  

> know.  But even when you aren't talking about light through water, the square
> of the distance thing still applies.  Even with spot lights.

There is no attenuation by the inverse square law, provided the ligth fixture
spreads out its output evenly over the entire tank surface. Such as from a
fluorescent hood with tubes/reflectors covering the entire surface. The
opposite situation takes place with fixtures that are small compared with
the tank surface area, such as with MH pendants and spot ligths. These are
effectively attenuated by the inverse square law since the ligth that
penetrates under the surface does not reach the glass walls before striking
on submerged objcts and being scattered out. Btw this is the same principle
behind the design of couplers used in fiber optics cables.

- Ivo Busko
  Baltimore, MD