photometrisch

Photometrisch refers to photometry, the branch of science that measures light as it relates to human vision. In contrast to radiometric quantities, which quantify radiant energy irrespective of perception, photometric quantities weight spectral power by the human eye’s sensitivity. The term is used across disciplines such as astronomy, optics, photography and lighting engineering.

The central photometric quantities include illuminance (lux), luminance (candela per square meter), luminous flux (lumen) and luminous intensity (candela). These quantities are derived from spectral power distributions by applying the photopic luminous efficiency function V(λ), which describes how the eye’s sensitivity varies with wavelength. Photometric measurements require calibrated detectors and reference standards to ensure comparability. Common instruments are photometers and calibrated photodiodes or photomultiplier tubes, often connected to measurement chains traceable to SI units, with the candela serving as the base unit for luminous intensity.

Applications of photometry span astronomical brightness measurements, where magnitudes and light curves are determined, to architectural lighting design and display technology, where luminance and illuminance inform qualitative and quantitative assessments. In astronomy, photometric systems (e.g., UBVRI, Sloan Digital Sky Survey filters) standardize observations and enable comparison across instruments and epochs. In color and vision science, photometric methods underpin colorimetric measurements and exposure planning. Overall, photometric methods translate physical light into perceptually meaningful quantities, aligning optical measurement with human visual response.