fotometre

A fotometre, or photometer, is an instrument designed to measure light. The term covers a range of devices used to quantify either the radiant energy of a light source or the brightness as perceived by the human eye. In photometry, measurements are converted into units meaningful for human vision, such as illuminance or luminous intensity, rather than pure radiometric power.

Photometric measurements rely on a light detector whose response is matched to the human visual system. The detector output is often transformed into units like lux (illuminance on a surface) or candela (luminous intensity) or into a calibrated display for exposure values. Many photometers use a standardized luminous efficiency function, V(λ), to weight the spectral content of light.

There are several common types of fotometre. Incident photometers measure the light falling onto a surface from a given direction, while reflected or spot photometers gauge light reflected from a surface to estimate apparent brightness. Integrating-sphere photometers collect light from a source in all directions to determine total luminous flux. In photography and filmmaking, exposure meters estimate the exposure needed for proper image brightness. Detectors can include photodiodes, photomultiplier tubes, or other calibrated sensors, sometimes with filters to target specific spectral ranges.

Applications span photography and cinema to workplace lighting design, architectural planning, horticulture lighting, and laboratory calibrations. Photometers are used to ensure safe illumination levels, to calibrate displays and sensors, and to study the lighting performance of sources and systems.