8. Quantities for photometry
8.1 Candela: definition
The candela, the SI base unit for photometry, was defined in 1946 (it was then called the "new candle") and its definition was taken up again in 1967 in the following form:
The candela is the luminous intensity, in the perpendicular direction, of a 1/600,000 square meter surface of a black body at the freezing temperature of platinum under a pressure of 101,325 pascals.
This definition was the result of work undertaken around 1930. At that time, when photometric measurements were made visually, a white light standard was needed, whose color was analogous to that of older standards and light sources in use. The practical application of the candela based on this definition...
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Quantities for photometry
Quantities for ionizing radiation
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