On Wed, 16 Jul 2003 12:07:05 GMT, (Joseph O'Neil) wrote:

You see (poun intended), nto all peopel with so called
"normal" colour see colour the same. Teh textbook answer is people
with "normal " colour vbision see from 400nm (violet) to 700nm (deep
red). But evidence has shown some peopel see well into the near
ultra-violet...

Interestingly, there is a UV sensitive chromophore in one population of cones
(response range 300nm-385nm, peak 342nm.) However, these cones normally are very
insensitive because UV is absorbed by structures in the eye before it can get to
the retina. The strongest absorber is the lens, which yellows with age, passing
less and less blue and UV. Eventually, cataracts develop and the lens is
removed. In recent years all replacement lenses include UV blockers, but plenty
of people are around who don't have these, and they have quite good UV
sensitivity. The same for children, with lenses that still pass shorter
wavelengths.


Some peopel cna also see
into the near IR according to some theories...

Although there is no specific IR receptor, the long-wavelength toe of the red
receptor extends quite far past the usually specified 655nm cutoff point, and
this chromophore has the highest QE of all. So any normal eye can see quite far
into the IR if the light is bright enough. This is easily observed with IR
remote controls. In a dark room, you can often see the emitter flashing dimly
red. What you are seeing is a fairly monochromatic light source operating
between 850-940nm.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com