> Darren New<dne### [at] sanrrcom>  wrote:
>> On 9/17/2011 18:21, Tim Cook wrote:
>>> On 2011-09-17 08:47, Darren New wrote:
>>>> I think asking whether it's the eyes or the brain doing the
>>>> interpretation is an over-simplified question. :-)
>>>
>>> Well, was thinking more about the reception of the direct input from the
>>> rods and cones, separate any other processing. Sort of a..."is the colour I
>>> see as 'blue' the same colour you see as 'blue'?"
>
>> The different rods are definitely responding to different wavelengths.
>> Whether the same wavelengths correspond to the same colors is a different
>> and so-far-unanswered question.  I.e., "blue" is the same wavelength for
>> everyone, but "blue" is a subjective experience.
>
>    It becomes even more complicated when you consider that combinations of
> different wavelengths may look the same to the human eye, yet may have
> different physical properties (eg. when reflecting from surfaces).
>
>    For example, a light consisting of one single wavelength, pure yellow,
> may look to the human eye the exact same color as another light with two
> wavelengths, a certain amount of pure red and a certain amount of pure
> green. While these two types of light are, physically speaking, completely
> different, they may look exactly the same to the human eye (ie. the second
> light also looks pure yellow even though it has no yellow wavelength in it
> at all).

Some persons will not see the red + green as yellow but rather as some 
shade of orange or yellowish green.

>
>    (The reason why we are able to see a pure yellow wavelength even though
> we don't have "yellow" receptors is that the red and green receptors also
> receive wavelengths from around those two wavelengths, including yellow.)

Some persond, mostly women, do have yellow receptors in addition to the 
usual red, green and blue ones.
It give them an edge in identifying plants and fruits.

>
>    Even though the two lights look the same color, they may illuminate
> surfaces in different ways. That's because surfaces may reflect different
> wavelengths in different ways. For example, if we had a surface that
> reflected only the pure yellow wavelength, it would look yellow under
> the first light but almost black under the second light. (That's the
> reason why some lights make everything look "spooky" and unreal. This
> is usually because they are composed of a combination of sharp wavelength
> curves, rather than being an about evenly-distributed white light that
> emits all visible wavelengths almost equally. "White" leds are a good
> example of this.)
>
>    Also, there's the fact that the human eye can perceive more colors than
> a normal RGB monitor can emit (which means in practice that not all
> photographs can be accurately presented with an RGB monitor).
>

Another example is the krypton headlight you find on some cars. They 
emit close to nothing in the yellow range. This makes some bright yellow 
cars appears as very dark gray.
Those also effectively suppress your night vision as they contains to 
much blue and violet.

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