Re: Human perception of infrared

["Henning J. Wulff" <henningw@xxxxxxxxxxxxxx>]

Aaron Ferrucci wrote:


>> The wavelength of red light is around 750nm. I believe this equates to
>>  0.75mm. If you were to hold a red object such that it almost touched the
>> surface of the eye (say half a millimetre away) you would presumably be able
>> to perceive it as being red. Yet the light reflected from the object would
>> have travelled less than a full wavelength before striking the eye. What
>>am I
>> missing here?
>>
>
>I can help a bit here: 750nm is actually .75 micrometers, or
>.00075 mm.
>
>I think the distance of interest is not the distance from
>the red object to the eye, but from the red object to the
>retina.
>
>The question then becomes, what happens if you suspend a
>red object 500nm from the retina (please, let's leave this
>as a gedanken physics experiment, rather than try to figure
>out how to actually _do_ this without destroying someone's
>eyesight!).   Of course only a few retinal cells would be
>that close to the light source...
>
>Well, that's as far as I can go - can anyone with a better
>biophysics background shed some light?

How close the retina or individual cells are to the eye is not important;
the red light exists before it hits the red object. The red object just
filters the other colors out.


   *           Henning J. Wulff
  /|\     Wulff Photography & Design
 /###\      henningw@xxxxxxxxxxxxxx
 |[ ]|     http://www.archiphoto.com


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