In sci.space.policy Dennis M. Hammes wrote:
Ian Stirling wrote:

In sci.space.policy Christopher James Huff wrote:
snip
Well, we really are practically blind. Our eyes are trichromatic

Monochromatic-with-filters; or "quadrichromatic." But not "tri-."
11-cis retinal is the /only/ photosensor we've got.
The three oil filters (assorted among the "cones") reduce the
incident light level considerably, not the sensitivity.
Same happens putting color filters on a camera or litho
separations.

sensors, with limited resolution and only capable of giving very crude
estimates of color, lightness, and size. We can not see spectral

Looking at the spectral sensitivities, it's amazing there is
any vivid contrast between red and green at all.

Heh. Some few people have none whatsoever.
Monochromatic contrast is /all/ in the filters.

The two sensors are so similar that the difference in sensitivity
at any given wavelength between red and green is quite small.

Actually not; we are rather more sensitive to green by at least
e=hf.
Why subs and planes are set "cockpit red" at night.

That's to optimise the low-light sensitive cells, which are different
to the ones that are used to sense colour vision, and very insensitive
to red.

They are most sensitive to green light, but a slightly different wavelength
green to the one that the green cells used to sense colours.

Normalising the sensitivity, where 1 is the sensitivity peak.
The differences are fairly small, compared to the differences between
them and blue.

red green blue
658nm .1 .085
600nm .8 .3
570nm 1 .8
554nm .96 .96
542nm .9 1
513nm .5 .7
503nm .32 .47 .1
442nm .04 .07 1
456nm .06 .1 .84