Color Perception And Your Retina

Beautiful Morning

Camera: Leica M9
Exposure: 1/1000
Aperture: f/2
Focal Length: 50mm
ISO: 400

I love the subtle color that emerges as we come out of the mesopic vision range into early sunrise and late sunset while still in the shadow of the Earth.  This of course is the phenomenon that inspired Jan Evangelista Purkyně to come up with his theory on two visual systems of the eye, one designed to see bright overall light intensity and the other adapted for the mesopic range before dawn and after dusk.  This is the shift in colors that we perceive, where reds appear brighter in the bright daylight and darker, more muted around dawn and dusk.  In other words, the maximum sensitivity to luminance of the human eye shifts towards the blue portion of the spectrum at low levels of illumination.

The mechanism of this shift is based in the neural circuitry of the retina and in particular, circuits that are mediated by the AII amacrine cell which is intimately involved in the switch between your rod mediated, low light vision and your bright light, color perception mediated by cones.  Making that switch is not a trivial task, but learning how a couple hundred million years of evolution has refined this neural processing is exciting work.

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