In article , NetMax
wrote:

"David C. Stone" wrote in message
...
[snip]

Water also absorbs very strongly across the IR band. I'm not sure
how much IR you would get in a fish tank, but I'm guessing not very
much and only select wavelengths at that.

My very limited understanding is that the longer the wavelength, the
lower the rate of attenuation. Water is blue because the shorter
higher-frequency blue is attenuated first and longer wavelength red
travels deeper. Similarly, lower musical notes travel further
underwater. Based on that logic, infrared should go further than visible
light with its longer wavelength, but longer is a relative term ;~),
water is a good attenuator.

I think you're thinking of light scattering, which is one mechanism for
light attenuation. Once beyond scattering, though, you have to take
absorption into account. Water is very good at absorbing IR and
microwave energy.