lightmeasuring

Lightmeasuring refers to the set of methods and instruments used to quantify properties of light, including intensity, color, and spatial distribution. It supports design, evaluation, and compliance in fields such as architectural lighting, photography, display calibration, horticulture, and occupational safety.

Measurements are categorized as radiometric or photometric. Radiometric quantities quantify radiant energy independent of human perception, using units such as watt and radiant flux. Photometric quantities reflect the eye’s response and are expressed in lumen for luminous flux, lux for illuminance, and candela per square meter for luminance. Radiant and photometric data are related through the luminous efficiency function V(λ).

The CIE standard observer and the V(λ) function underpin photometric calculations. Luminous efficacy describes how effectively radiant power is converted into perceived brightness, typically expressed as lumens per watt.

Common instruments include photometers and lux meters for general illuminance, spectroradiometers for spectral power distributions, and integrating spheres for total flux measurements. Colorimeters and spectrophotometers are used to characterize color appearance. All measurements rely on calibration against traceable standards to ensure comparability.

Applications span lighting design and energy modeling, workplace safety compliance for permissible exposure, camera and display calibration, and research in horticulture and human-centric lighting.

Standards are developed by the CIE and coordinated with ISO and IEC. The CIE publishes definitions for color spaces such as XYZ and for measurement geometries, spectral data, and observer models, while ISO/IEC standards address instruments, procedures, and performance requirements.

Lightmeasuring emerged from early photometry in the 19th century and matured with the formation of the CIE in 1913 and its subsequent publication of luminous efficiency and colorimetric standards in the 1920s and beyond.