Embodiments include a control apparatus, a control method, and a control system that can effectively utilize an index regarding light incident on a measured object by obtaining the index effective for the measured object. The control apparatus can effectively utilize an effective index by controlling improvement of an environment that affects calculation of the effective index on the basis of the effective index representing an index that is related to light incident on a measured object and that is effectively utilized for the measured object. The measured object may be a plant.