[mwambua]

> The human eye is most sensitive to green light, so that channel effectively carries the majority of the luminance (brightness/detail) data

How does this affect luminance perception for deuteranopes? (Since their color blindness is caused by a deficiency of the cones that detect green wavelengths)

[fleabitdev]

Protanopia and protanomaly shift luminance perception away from the longest wavelengths of visible light, which causes highly-saturated red colours to appear dark or black. Deuteranopia and deuteranomaly don't have this effect. [1]

Blue cones make little or no contribution to luminance. Red cones are sensitive across the full spectrum of visual light, but green cones have no sensitivity to the longest wavelengths [2]. Since protans don't have the "hardware" to sense long wavelengths, it's inevitable that they'd have unusual luminance perception.

I'm not sure why deutans have such a normal luminous efficiency curve (and I can't find anything in a quick literature search), but it must involve the blue cones, because there's no way to produce that curve from the red-cone response alone.

[1]: https://en.wikipedia.org/wiki/Luminous_efficiency_function#C...

[2]: https://commons.wikimedia.org/wiki/File:Cone-fundamentals-wi...

[doubletwoyou]

The cones are the colour sensitive portion of the retina, but only make up a small percent of all the light detecting cells. The rods (more or less the brightness detecting cells) would still function in a deuteranopic person, so their luminance perception would basically be unaffected.

Also there’s something to be said about the fact that the eye is a squishy analog device, and so even if the medium wavelengths cones are deficient, long wavelength cones (red-ish) have overlap in their light sensitivities along with medium cones so…

[fleabitdev]

The rods are only active in low-light conditions; they're fully active under the moon and stars, or partially active under a dim street light. Under normal lighting conditions, every rod is fully saturated, so they make no contribution to vision. (Some recent papers have pushed back against this orthodox model of rods and cones, but it's good enough for practical use.)

This assumption that rods are "the luminance cells" is an easy mistake to make. It's particularly annoying that the rods have a sensitivity peak between the blue and green cones [1], so it feels like they should contribute to colour perception, but they just don't.

[1]: https://en.wikipedia.org/wiki/Rod_cell#/media/File:Cone-abso...

[volemo]

It’s not that their M-cones (middle, i.e. green) don’t work at all, their M-cones responsivity curve is just shifted to be less distinguishable from their L-cones curve, so they effectively have double (or more) the “red sensors”.