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Re: The blueness of water



On Sun, 28 Apr 2002, Brian Whatcott wrote:

At 02:13 AM 4/28/02, Bill wrote:
I think the light is still decreasing linearly at
those depths, so an internally-illuminated pool 10 meters deep would look
approximately as blue as a top-illuminated pool 5 meters deep.

My attention monitor tripped on this linear suggestion. I assume
by contrast, an exponential decrease of light in an ordinary absorber.

Exactly. An exponential decay initially resembles a straight line, that's
why I said "at those depths". When the water appears deep blue or black,
you're certainly too far along and the straight-line approximation doesn't
work.

But I'm ignoring the change in spectrum, and I forgot about the eye's
transfer function. That's why I prefaced it with "I think"

:)


And regarding salt water: sea salt is white. In so many words I'm
wondering if adding sea salt to a deep pool of fresh water would
significantly affect the color we see.

PS

Weird swimming-pool effect: some relatives in San Jose have an outdoor
inground pool with black walls. It's very hard to see the surfaces, and
unless the sun is casting shadows, the depth of the pool looks scary.
Stare down into it and imagine gigantic finned torpedo shapes gliding
around in the depths. Yeesh.

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