PROBLEM TO BE SOLVED: To provide a light-illuminating device utilizing the optical response of plant to efficiently cultivate the plant: and to provide a short-day treatment method for plant comprising using the light-illuminating device to solve various problems in light-shielding equipment. SOLUTION: The light-illuminating device 1 includes: a light sensor 5 which can selectively detect the strength of each of red light and far-infrared light; a light-illuminating part 4 which illuminates the red light and the far-infrared light so as to adjust the illumination strength of each of the lights; and a control part 3 adjusting and controlling the illumination strength of each of the red light and the far-infrared light from the light-illuminating part. The control part carries out a process of detecting the strength ratio of the red light and the far-infrared light via the detection output from the light sensor, and a process of illuminating the far-infrared light from the light-illuminating part so that the strength ratio of the far-infrared light becomes a prescribed value or more at either or both of the vicinity of the starting time and/or the vicinity of the end time of the photophase in a light cycle to control the photoperiodic reaction. COPYRIGHT: (C)2009,JPO&INPIT
