Photometry

Photons enter the eye through the optic lens, which, in the human eye, is controlled by muscles which flex it in order to focus the light on different portions of the retina, which absorbs the photon. Amongst the matter absorbing these photons are photoreceptive cells, rods, and cone cells. These cells are preferentially sensitive to light of varying wavelengths and intensity. The absorption of photonic energy catalyzes a reaction in a receptive protein molecule, of class known as opsins, creating a chain reaction of protein activity for the purposes of cell signaling. The degree and duration of this stimulus either excites or inhibits the cell, towards a threshold where the cell will be more or less inclined to fire, sending a bioelectrical signal to another kind of specialized nerve cell, as the first step of relaying the signal that carries information as to what has happened with that particular receptor into the optic nerve and ultimately into the brain, where the combined stimulus of all the receptors is amalgamated, filtered, and processed to create visual perception and the subjective experience of vision.

Rod cells and cone cells.

Photoreceptor cells convert light (visible electromagnetic radiation) into signals that can stimulate biological processes. Cone cells are photoreceptor cells in the retinas of vertebrate eyes and are responsible for color vision, functioning in bright light, whereas rod cells, work better in dim light. Rod cells have little role in color vision, which is the main reason why colors are much less apparent in dim light. There are 3 types of cone cells: S-cones, M-cones, and L-cones. When violet light strikes the eye, the S-cone is stimulated strongly, and the L-cone stimulated weakly.

There’s about 92 million rod cells in the human retina, and 4.5 million cone cells in the human eye.

Reflective light.

Most materials have some absorption cutoff where shorter-wavelength radiation cannot penetrate, because it moves an electron across a band gap. Metals tend to reflect radiation from radio waves to UV. But colored metals like copper and gold don’t reflect the shorter wavelength (Webb space telescope cannot see blue or UV reflected from gold).

In 2020, 3-Hydroxyisonicotinaldehyde (also known as 3-hydroxypyridine-4-carboxaldehyde), has the lowest molecular weight of all dyes, which exhibits green fluorescence.

Do animals see color?

Animals such as rabbits and alligtors, lack the red cone, but do have the blue and green cone. That generalls means they can see blue and green the same way we do, but not red.

Most birds see orange through ultraviolet. Few birds can see into the red range of the spectrum. Other animals like bumblebees cannot see into the red spectrum.