ABSTRACT
This chapter introduces the scientific principles of light, vision, and photometry that make television possible. Vision at low levels of illumination is called scotopic vision, which takes place at higher levels of illumination. If a spectrum is allowed to fall upon a narrow slit arranged parallel to the edge of the prism, a narrow band of wavelengths passes through the slit. A plot of the power distribution of a source of light is indicative of the watts radiated at each wavelength per nanometer of wavelength. Matching the resolving capabilities of the human eye is a commendable engineering goal, but a difficult proposition in any practical imaging system. The sensation characteristics as applied to any given stimulus depend in part on other visual stimuli in the field of view and upon the immediately preceding stimulations. In visual photometers, used in obtaining basic photometric measurements, the two stimuli to be compared are normally directed into small adjacent parts of a viewing field.
