In physics, photometry is the measurement of the luminous intensity of a light source, or the amount of luminous flux falling upon a surface from such a source. Photometry is important in photography , astronomy, and illumination engineering. Instruments used for photometry are called photometers. Light waves stimulate the humaneye in different degrees, depending on the wavelength of the light. Because it is difficult to make an instrument with the same sensitivity for different wavelengths as the humaneye, many photometers use a human observer. Photoelectric photometers need special collared filters to make them respond like the humaneye. Instruments that measure radiant energy instead of light are called radiometers, and must be made equally sensitive to all wavelengths. The intensity of a light source is measured in candle power, usually by comparing the source with a standard source provided by the National Bureau of Standards. The known and unknown sources illuminate portions of a window surface side by side, and their distances are adjusted until the illumination on the surface is the same. The relative intensity is then calculated from the inverse square law. Research Photometry
The National Bureau of Standards is an organization, founded in 1901, whose function is to establish and maintain standards for units of measurements. Research National Bureau of Standards
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Photometry
