PROBLEM TO BE SOLVED: To provide the subject system light in the burden on its maintenance, replaceable in its artificial light sources at a time, easy to conduct illuminance control, designed to make a control so as to uniformize the cumulative lighting time as a result of the lighting of plural artificial light sources for each specified time. SOLUTION: This system is so designed that the lighting number of plural artificial light sources L1 to L3 to expose a plant to light is controlled to ensure the light intensity of the sources L1 to L3 to be changed with a specified pattern made up so as to resemble the sunshine pattern, and a control is made so as to uniformize the cumulative lighting time as a result of the lighting of the plural artificial light sources L1 to L3 for each specified time. It is preferable that such a lighting pattern as to represent each unit lighting time continuously or intermittently as the lapse of a specified period of time is provided for each of the artificial light sources L1 to L3 so as to uniformize the cumulative lighting time after the lapse of a specified period of time.
