SI unit of luminous flux

Symbol: lm

1. luminous flux emitted in unit solid angle (steradian) by a uniform point source having a luminous intensity of 1 cd (defined by 9th General Conference of Weights and Measures, 1948)

2. equivalent definition: luminous flux of a beam of monochromatic radiation whose frequency is 540 × 1012 Hz and whose radiant flux is 1/683 W

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