The color we perceive from photons with a wavelength around 700 nm (nanometres).
In this way, even if what your brain calls "red" is different from what my brain call "red" (which could be your "green", for example), we can both agree that if a special light is designed to emit only...
Best answer: The color we perceive from photons with a wavelength around 700 nm (nanometres).
In this way, even if what your brain calls "red" is different from what my brain call "red" (which could be your "green", for example), we can both agree that if a special light is designed to emit only photons at that wavelength, then whatever our individual brains perceive, THAT is what we should both call "red".
Tomatoes can be red, green, yellow, mauve...; not reliable as a standard. When they arrived in Europe (imported from America by the Spaniards), the Italians called them "pomidori" (golden apples). The red hybrids came later.
Blood is red when iron is the metal that stabilizes the oxygen-bearing cells in the blood AND the cell is carrying oxygen on its way out of the lungs (not on the way back, when it carries CO2 -- it is then bluer). On Earth, land animals -- including ourselves -- have evolved with iron at the core of the "hemoglobin" molecule.
Some fish don't.
If is (chemically) possible to have blood where the molecule would use another metal. In Star Trek, Mr. Spock's blood uses copper, and that means his blood is greenish.
Thus blood (without specifying the species and the location of the sampling) is not reliable.
Heat is more readily felt from photons of longer wavelength (called infra-red, invisible to the human eye). Also, given enough light, you may feel some heat from lights of colors other than red.
A long time ago (mumblety-mumble years ago) I wondered how a [human?] person having evolved for hundreds of generations on a colony planet with a cooler star (around 4000 K instead of the 5400 K of our Sun) would interpret colors if their brain (similar to ours) still used "red, green and blue" as primary interpretations.
For that, I used Ektachrome film designed for near infra-red photography, and where the processing would lead to color-shifting:
Blue would become invisible (the use of that film required a yellow filter to prevent blue light from hitting the film)
Green would show as blue
Red would show as green
Near infrared would show as red.
If we were to converse with that person, we would have to establish what color is called red, and we would insist that it is the 700 nm photon, which, to that person, could look like our green.
2 weeks ago