Note 1 to entry: 1 lm is equal to the luminous flux of a beam of monochromatic radiation whose frequency is 540 × 10¹² Hz and whose radiant flux is 1/683 W.

Note 2 to entry: According to the 9^th General Conference of Weights and Measures (1948), the lumen is defined as the luminous flux emitted in unit solid angle (steradian) by a uniform point source having a luminous intensity of 1 cd.

Note 3 to entry: This entry was numbered 845-01-51 in IEC 60050-845:1987.