fotometrialla

Fotometria, or photometry, is the branch of optical metrology that quantifies visible light in terms of perceived brightness. It focuses on luminance-related quantities rather than raw radiant power, and is fundamental to lighting design, photography, astronomy, and display technology.

Photometric quantities include luminous flux (lumen, lm), illuminance (lux, lx), luminous intensity (candela, cd), and luminance (candela per square meter, cd/m2). These quantities are weighted by the luminosity function V(λ), which approximates the average human eye sensitivity across wavelengths, making photometric measurements respond to the eye’s perception rather than pure energy.

Instruments and methods: Photometers and lux meters perform photometric readings of light sources. In research and astronomy, detectors such as photomultiplier tubes, photodiodes, and CCDs are used with calibration against standard stars or laboratory light sources. Absolute photometry aims to determine true light output, while differential photometry compares target sources to reference standards to cancel systematic effects like atmospheric extinction.

Applications: efficient lighting design, ensuring consistent illumination levels; photography and cinematography for proper exposure; display calibration for televisions and monitors; and astronomical photometry for measuring the brightness of stars and other celestial objects. Photometric systems, such as the Johnson UBVRI system, provide standardized passbands for comparing measurements.

Relation to radiometry: photometry is a photometric form of radiometry. It converts radiant energy into a quantity weighted by human vision, whereas radiometry treats all wavelengths with equal importance. Both fields are essential for interpreting light in science and industry.