Mesopic Vision

Mesopic Vision is a fusion of Scotopic Vision and Photopic Vision systems at an intermediate environmental brightness. At these “Twilight” levels, both of these systems are active, since the light is dim enough that the Scotopic Vision is not Photobleached, but is bright enough that the Cone Cells can still be excited by the limited light.

Since both the Cones and Rod cells are active in Mesopic Vision, Conditional Multichromacy can yield Tetrachromacy in Color Normal humans.

See also Purkinje Effect.