Radiometry. Photometry

This article deals only with the metrological aspects of characterizing optical radiation, sources, propagation in media, properties of samples and passive objects, and detectors. For a description of the structure and properties of sources, media and detectors, the reader will find several references in the bibliography of the fact sheet. .

As we shall see, photometry, taken in its broadest sense, is a difficult art, due to the complexity of the spatial and spectral distribution of radiation. For this reason, metrologists have been led to define a relatively large number of quantities that can be measured without too much difficulty, as we shall see. This complexity also means that the precision of photometric measurements often appears mediocre: a relative uncertainty of 1% corresponds to good current precision, while 10 ^{– 4} is quite exceptional.