Scotopic vision is the vision of the eye under low-light levels. The term comes from Greek Skotos, meaning "darkness", and -opia, meaning "a condition of sight". In the human eye, cone cells are nonfunctional in low visible light. Scotopic vision is produced exclusively through rod cells, which are most sensitive to wavelengths of around 498 nm (green-blue) and are insensitive to wavelengths longer than about 640 nm (reddish-orange). This condition is called the Purkinje effect.