Why are geckos nocturnal?

The eye of a gecko is red so it's nocturnal. The eye - actually, to be more specific, the retinae, of a gecko is the reason why geckos are nocturnal. It's rather complicated to explain, but to make it short, the reason why geckos are nocturnal is due mostly the arrangement of cones and rods in the eye of a gecko. The cones and rods are description that is given to the shape of cells in the eye that help with sight, but they are also referred to as such.