Evolution of human colour vision as 'visual purple' receptor proteins, are encoded by Rh1, OPN2 and RHO genes. They are characterized by extreme sensitivity to light and enable monochromatic human vision in low light or dim conditions. They are broken down into retinal and opsin when exposed to these conditions. Humans have 3 types of photopsin proteins found in the cone cells. Long Wavelength Sensitive Opsin (Red cone opsin) – Encoded by the OPN1LW gene with a λmax of 560 that is found in the yellow-green electromagnetic spectrum despite its name. Its sensitivity to the colour red is still known to be higher than the
Human eye hampered by retinal disease, poor vascular circulation and high altitude exposure. The human eye can detect a luminance range of 10, or one hundred trillion (100,000,000,000,000) (about 46.5 f-stops), from 10 cd/m, or one millionth (0.000001) of a candela per square meter to 10 cd/m or one hundred million (100,000,000) candelas per square meter. This range does not include looking at the midday sun (10 cd/m) or lightning discharge. At the low end of the range is the absolute threshold of vision for a steady light across a wide field of view, about 10 cd/m2 (0.000001 candela per square meter).