Fotomeetria

Fotomeetria, also known as photometry in many languages, is the branch of optical metrology that measures light according to human visual perception. It focuses on how the eye perceives brightness rather than the total radiant power. Photometric measurements are weighted by the human eye’s luminosity function, typically denoted V(λ), to reflect differences in sensitivity across wavelengths.

The field defines several key quantities. Luminous flux (measured in lumens) describes the total perceived power of light. Luminous intensity (candela) quantifies the light emitted in a given direction. Illuminance (lux) measures the perceived power per unit area on a surface, while luminance (candela per square meter) characterizes the brightness of a surface as seen by an observer. These photometric units are standardized by international bodies such as the CIE and ISO.

Instruments and methods include photometers and lux meters for routine measurements, goniophotometers for angular light distributions, and integrating spheres for total radiant flux with uniform sampling. Measurements may involve spectral weighting by V(λ) to yield photometric results from spectral data.

Fotomeetria is distinct from radiometry, which quantifies radiant energy independent of perception. Standards and calibration procedures ensure consistency across instruments and applications. Practical uses span architectural and interior lighting design, display calibration, photography and cinema lighting, automotive lighting, and horticulture, among others.