The ability of the human eye to perceive light is truly one of the wonders of nature. Incredibly complex and delicate, the human eye is sensitive to a remarkable range of light levels and detail. This chapter explores the characteristics of the eye and human vision to better understand the components of compelling nightscape images. The ability to perceive the different colors of light is surely one of life's greatest joys. The spectrum of our sun contains every wavelength of light, and is referred to as white light. Photography is the collection and rendering of ambient light. The human eye has several characteristics worth appreciating from a photographic perspective, especially for night photography. Dark adaptation is the name given to the physiological process by which the rods in our retina increase their level of photopigments until they are nearly a million times more sensitive to light than in full daylight.