An instrument for measuring the luminance, luminous intensity, or illuminance of a light source. Analogous to radiometer, but with an output weighted by the wavelength response of the human eye (i. E. , scaled by luminous efficiency). It is common in historical literature to see this term used for any radiometer that responds primarily to wavelengths that are visible to the human eye, with or without scaling for luminous efficiency. A photometer used to measure the intensity of a distant light is sometimes referred to as a telephotometer or transmissometer. See hydrophotometer, radiometer.