Re: Visibility and wavelength

[shawl@torchlake.com (Jonathan Shawl)]

Paul Anderson wrote:

> Long wavelength == IR
> Short Wavelength == Ultraviolet
>
> Those are the two ends of the light spectrum, and frequency is inversely
> proportional(IIRC) to wavelength, so the lower the frequency, the larger
> the wavelength.  If you're talking about millimeter wavelengths, then
> you're talking stuff like 2.4GHz radio, and at those frequencies water
> sucks it up like lead plate.  That's why radar doesn't work under water(in
> fact, that's also why nuclear fuel rods are stored in deuterium oxide,
> heavy water).  That's also why the sky is blue, and the ocean is blue.

I agree, that is what I thought.

> With the sky, longer wavelengths than blue are blocked by the ozone
> layer(guess what causes sun burns(which are in fact radiation burns) and
> is the principle agent of heat?  yes!  IR!).......      Paul Anderson

Oops, just a second on that one, let me have a stab at it. I had to study up on this
to get my CFC handling license. The ozone layer is the layer that blocks the
damaging UV light. The chlorine in CFC's damage the ozone layer and that lets in
more UV which causes us to burn more. It is the UV light that damages you skin or
gives you the "sun burn", and it is the IR that makes you feel hot. Tanning beds are
full of blue UV lights and can burn you without feeling the heat.  You can get a bad
case of "sunburn" in about a minute by close exposure to an electric arc welder in
operation, and you don't feel much heat. I know, I have done this to my self way to
often. On the other hand you can sit next to a IR emitting wood stove or  IR heat
lamp all day and get real warm, but not get "sunburn" at all. Another example of
this is the UV block you put on before you go to the beach. It reflects the damaging
UV ray, but the IR gets to you and still makes you feel hot.  Take a look at your
arm under a "near UV" black light after you put on clear looking sun screen. It
almost looks like you painted your arm white.
Anyway, we are still in the dark underwater.
Anybody ever try a black light underwater?
Jonathan Shawl