Fotometrii

Fotometrii, or photometry, is the branch of optical measurement that treats light in terms of human visual response rather than purely radiant energy. It concerns how bright a light source appears to an observer and is essential for lighting design, vision research, photography, and astronomy.

The core photometric quantities are luminous flux (lumen, lm), illuminance (lux, lx), and luminous intensity (candela, cd). Luminance, measured in nits (cd/m^2), describes the brightness of a surface as seen by the eye. Photometric measurements weight spectral power by the standard luminous efficiency function V(λ), which captures the eye’s sensitivity across wavelengths. Radiant quantities, such as radiant flux (watts), are related but not equivalent to photometric values because they do not account for human perception.

Instruments and methods used in fotometrii include photometers and lux meters for measuring brightness and illuminance, as well as integrating spheres to determine total flux. Detectors such as silicon photodiodes, photomultiplier tubes, and photocells convert light into electrical signals that can be calibrated against standards. Photometric data are often corrected for observer effects, spectral content, and geometry to ensure comparability.

Applications span several fields. In lighting engineering, photometry guides illumination design and energy budgeting. In photography and cinematography, it informs exposure and color rendering. In astronomy, photometry measures celestial brightness in standard passbands (for example UBVRI) and underpins magnitude systems, allowing comparisons of objects across the sky. Absolute photometry uses standardized references to determine true fluxes, while relative photometry compares sources under controlled conditions.

Historically, fotometrii developed with the adoption of the CIE standard luminous efficiency function and the redefinition of lumen and candela. It remains integrated into international standards for lighting, display, and optical instrumentation.