Creation Moment 2/2/2023 - Q: Why a Green Earth? A: Easiest on our Eyes

I will praise thee; for I am fearfully and wonderfully made: marvellous are thy works;

Psalm 139:14

"Why is green the most important color for the human eye?..... the
makeup of the human retina, which broadly contains two types of cells, rods and cones, which (very broadly) equate to pixels on an imaging sensor. 

Rod cells are highly sensitive with a peak of sensitivity at or above 500nm, which is sort of the border of blue moving into green. There are around 100 million of them in the human eye (some sources say 120 million), which is way way more than the six (or so) million color-sensitive cone cells. It's therefore tempting to leap to the conclusion that we see green sharply because there are more rods than cones and rods see green best.

That doesn't quite work out, though, because the moment we actually look at anything, we move our eyes so that the region of interest falls on the central area of the retina. Most of the color-sensitive cone cells are in this area; there aren't so many rods. This part of the retina is good for seeing sharp detail because each of the (roughly) nerves that take signals from cone cells to the brain is only connected to one cone cell. By comparison, quite a lot of rod cells are connected to each (roughly) nerve, which is good for sensitivity, because we're adding an up signal from a lot of (kinda) pixels, but not so great for sharpness.

So that's why the central area of vision is sharper. What we've heard so far, though, suggests that our daytime color vision should be sharper than our — in effect — monochrome night vision. It is, but it gives us no reason to assume that we should see green more sharply than red or blue. The reason for that is simply in the sensitivity curves of the three types of rod. It's often said that we have red, green and blue-sensitive rod cells, which is sort of true, but much as with a Bayer-pattern electronic image sensor, there's a lot of overlap between the three types, to the point that the medical world calls them long wavelength, (reddish), middle wavelength (greenish) and short wavelength (bluish) — but they really see a lot more than a single color.

To see saturated color, the brain does more or less the same sort of

processing that has to happen in a Bayer-sensor camera in order to recover full-color information. The reason this gives us best acuity in green is simply that there's really a lot of overlap between the medium and long (green and red) cones. This happens to the point where the medium-length cones can see everything from a greenish turquoise all the way through to, well, a fairly orange yellow, while the red cones can see from mid-green to the borders of infra-red. The result is an overall peak of sensitivity at a place which really looks pretty green, despite the fact that we can also see red using the same anatomy.

So, the highest-density, sharpest part of the retina is most sensitive to greenish light." Redshark