– the intergovernmental organization through which Member States act together
     on matters related to measurement science and measurement standards.
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International metrology in the field of Photometry and Radiometry

Radiometry is the field of metrology related to the physical measurement of the properties of electromagnetic radiation, including visible light.

Photometry describes the effects of visible light on the human eye, in terms of brightness and colour.

The two fields and their units are closely related through the current definition of the SI base unit for the photometric quantity luminous intensity: the candela. The candela is the only SI base unit related to a fundamental biological process: human vision.

Radiometric and photometric measurements are of importance for a wide range of industries and applications, including the lighting, space, semiconductor, photovoltaic, optical communication, automotive and colour industries, displays and imaging, and climate change. Other emerging fields include appearance, terahertz applications, photonics, and quantum-based information.

Traditionally, metrology in both radiometry and photometry is based on primary radiation detectors (cryogenic radiometers) and on primary radiation sources (blackbody radiators, electron synchrotrons). Recent advances in the manipulation of individual photons show great promise of producing within a couple of years radiant fluxes with a well-established number of photons. At the same time the development of new types of instruments operating with single photons will require advances in new quantum-based calibration methods. The trend towards solid-state lighting requires the development of new calibration methodologies adapted to the properties of these light sources.

Photometry and Radiometry
Photometric units
Committee structure
Strategic plan
International equivalence

At the BIPM
BIPM liaison and coordination work
BIPM contact person