In the Neuroscience book edited by Purves et al. (page 232), it can be reading: “The reason for this unusual arrangement (rods and cones are active in the “dark” and inactive in “light”) compared to other sensory receptor cells is not known”!
I think the reason could be this:
To human beings can “see” places where come from few photons as a cave entrance or not “visible” photons from black painted surfaces, uses the following trick:
1.- When none or few visible photons are reaching the retina, rods and cones are active and releasing their transmitter.
¿Why? Because with their activity are producing the sensation of “Darkness”; black is a positive sensation; the blind eye does not “see black”; it “sees nothing” (W. Ganong in Medical Physiology, 22 edition, page 163).
2.- When some few photons reach retina, rods will inactive and produce the sensation of nocturnal vision (without color sensation). Meanwhile, cones still keep active.
3.- When a lot of photons reach retina, cones also will inactive and produce the sensation of diurnal vision with color sensations. Then, rods will saturate.
In other worlds, “dark” is a “background”, “filling” or “stuffing” in the visual field, otherwise, poor illuminated areas or objects will be, not “dark”, but invisible!
In poetic words: “Photons write on the retina, as a chalk on a blackboard”!
We must say, instead of "being in the dark or light", "being in absence or presence of photons" Ja, ja, ja.
http://www.propeller.com/story/2010/03/19/191why-do-we-see-dark191why-do-we-see-dark/
