Re: lighting for 8'x2'x2' tank

Alan Van nevel wrote:
> Why do people keep insisting on metal halide, HO or VHO for the 2foot depth?
> The intensity does fall off at 1/r^2,

You are quite right Alan in asserting that the depth of the tank is not
a factor in the intensity of light required. The requirement is based
on the _volume_ of the tank which determines how much plant material
is able to grow in it. Light attenuation is not a factor and virtually
all direct light which enters the top of the water remains in the tank
due to internal reflection. The 1/r^2 law does not apply in this situation.
There was an extensive discussion of this phenomenon a while back in the
APD. To demonstrate that light is trapped internal to the tank, stick
your eyeball right next to the tank glass and look up and try to see the
light through the glass. You won't be able to.

Steve in Vancouver where the temperature in our apartment is 78F (tropical)