Photometry is the branch of science that deals with the measurement of light, particularly in terms of its intensity and the way the human eye perceives it. It involves the quantification of visible light and its characteristics, such as brightness and color. Photometric measurements often consider the spectral sensitivity of the human eye to different wavelengths of light and use standardized units to express light intensity.
In astronomy, photometry is used to study the brightness of celestial objects, helping astronomers understand their properties and behavior. In physics and engineering, photometry plays a crucial role in the design and evaluation of lighting systems, as well as in the analysis of optical instruments and displays. The measurements in photometry are typically expressed in units such as lumens, lux, or candelas, which are related to human perception of light.