Scotopic Vision is usually used at night by humans or otherwise in dim environments (e.g. deep sea habitats). Due to several adaptations, the Rod Cells are more sensitive to light than Cone Cells, and can be activated by a single photon.
Scotopic Vision in humans and most other known vertebrates concerns only the Rod Cells and therefore Rhodopsin (Scotopsin). Since Rhodopsin is not expressed in multiple genes/alleles with different Peak Wavelengths (Rhodopsin always has a peak wavelength at 500nm), Opponent Channels between multiple classes of Rod Cells is not possible and Scotopic Vision is therefore always Monochromatic. This applies to most vertebrates, though some have been found to have multiple classes of Rod Cells, such as the Silver Spiny Fish, and may therefore have Polychromatic Scotopic Vision.
See also Mesopic Vision.