Photometry (optics)

For other uses, see Photometry (disambiguation).

Photometry is a branch of optics that deals with measuring light in terms of its perceived brightness to the human eye. It is concerned with quantifying the amount of light that is emitted, reflected, transmitted, or received by an object or a system.

Photometric quantities (e.g., luminous flux) are related to their radiometric analogs (e.g., radiant flux) through standardized luminous efficiency functions that model the spectral sensitivity of the human visual system. Typically, this wavelength-dependent weighting function is the photopic sensitivity function, although the scotopic function or other functions may also be applied in the same way. The weightings are standardized by the CIE and ISO.

Photometry is a branch of radiometry. Radiometric quantities are not limited to light (i.e., cover other kinds of optical radiation and are sometimes extended to other kinds of electromagnetic radiation) and are not spectrally weighted.

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