Understanding Cones (Eye) and Light

Hi guest,

You should sign in and become a member, you'll find a lot of answers here, some may even be good.

I'll try and answer your questions above. Your first question seems to be:

"if red wave enters eye, only red-cones response (y-n?)No. So when you see a red clothing, you see red because only the red wave reflect off it, all other waves absorbed by the pigments in garment (y-n?)Basically, Yes."

Actually all the cones respond to different degrees. That's because in nature there never is just red light or blue light, there are spectrum with peaks at red or blue. And the three cone types in the eye don't just detect red or blue or green, they detect spectrum with peaks at these colors, please see the spectrum for the three cones below:

And here is the spectrum of various light sources:

Which produce light that is reflected or are absorbed by objects. Then the reflected light from the surface is a spectrum (which can depend on the light spectrum hitting it). For instance:

Which then is absorbed by the color cones in the eyes to different degrees base on their detection spectrum. Since the different cones react to the same light differently, your brain can "triangulate" the color. Hopefully that makes sense to you.

Here is a great article from wikipedia providing additional information.

http://en.wikipedia.org/wiki/Trichromatic_color_vision

Your next question was:

"Now, are not red waves nearest infra-red and have best penetrating power (y-n?)Sometimes" -

Penetrating power depends on the what you're trying to shine light through. For instance some glass is transparent to visible light but reflects infrared (its how greenhouses work). On the other hand, zinc selenide is transparent for red and a lot of IR but not for the rest of visible (which is why it's reddish orange, see below):

Your next question was:

So why when deep underwater red colors dissappear first or not true? Is not plenty of red waves down to reflect off?! What is missing.

Ok, to answer that question, lets look at Water's Absorption Spectrum:

Hopefully you can see that blue is absorbed less than red from the chart above. In water, blue light has more penetrating power than red. So imagine shining a white light onto water. White light has all the colors in it in a spectrum. Now, as the light travels down into the water, the red in it is absorbed quicker than the blue, so if you go down deep enough, all you have left is blue light.

Deep sea animals actually exploit this with red coloring. You see, if you shine white light on a red animal like a crab, they appear red because the red light in the white light is reflected. However, as we have just seen, red light doesn't penetrate far into water, meaning only blue light gets very far. When you shine blue light on a red animal it looks....black, of course, because nothing is reflected (or very little). It's camoflage!

Here's an interesting link that talks about the red color of ocean animals as camoflage:

http://oceanexplorer.noaa.gov/explorations/02hudson/background/edu/media/hc_bright_red.pdf

Ok, I hope I've answered your questions. Good luck.

Roger