PROBLEM TO BE SOLVED: To provide an automatic dimming method and apparatus which have a simple configuration, a low manufacturing cost, and can give light intensity at which plants can always perform appropriate transpiration and photosynthesis.SOLUTION: In an automatic dimming control method for tomato cultivation, time when a photosynthesis rate after light intensity is changed becomes a stable state is a measuring period of light intensity by light intensity detection means, light intensity in the strongest range where a photosynthesis rate and a transpiration rate are set within an allowable range is an upper limit threshold value, light intensity at which photosynthesis rate is set to the lowest range within an allowable range is a lower limit threshold value, a light shielding material is set to a light shielding state in the case of the upper limit threshold value or higher, the light shielding material is set to an unshielded state in the case of lower limit threshold value or lower, and the light shielding material is set to a current condition maintained state in the case of lower than the upper limit threshold value and higher than the lower limit threshold value.SELECTED DRAWING: Figure 1
