(1) Lux 的定義是流明每平方米 (lumen/m^2)
(2) Lumen 的定義為 "the luminous flux emitted in a solid angle of one steradian by a point source having a uniform intensity of one candela",簡單的說就是一燭光的均勻點光源在一度 solid angle 內的光通量。(solid angle 及steradian 如果不明白可查維基百科)
(3) 燭光(candela)為一基本SI單位,依據1979年第十六屆CGPM會議,其定義為"the luminous intesity, in a given direction, of a source that emits monochromatic radiation of frequency 540 * 10 ^12 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian",換言之,一燭光是指光源的 540*10^12 hertz的頻率單色光在一特定的方向擁有每度solid angle 1/683 瓦能量的光強度。