"lumen n, pl lumens also lumina [NL lumin-, lumen, fr. L, light, air shaft, opening] (1873) . . . 3 : a unit of luminous flux equal to the light emitted in a unit solid angle by a uniform point source of one candle intensity—luminal also lumenal adj."*
*Merriam-Webster's Collegiate Dictionary, 11th ed., 2004.