In a device a crop is cultivated in an at least substantially daylight-free environment, wherein the crop is exposed in an at least substantially fully conditioned cultivation space (10) to actinic artificial light from an array of artificial light sources (30) present in the cultivation space. During a cultivation cycle a power output of the artificial light sources (30) is adapted to an energy absorption of a part of the crop (50) illuminated thereby such that the crop close to each of the array of artificial light sources is subject to an at least substantially constant and at least substantially mutually equal vapour deficit.