1. An address determining method for determining, in a lighting system including luminaires, image sensors which perform lighting control for the luminaires, and a controller which gives the image sensors an instruction regarding lighting of the luminaires, a positional relationship among the luminaires and the image sensors; the method comprising: inputting map data to an external terminal indicating layout of the luminaires, the image sensors, and the controller; receiving, by the controller, an external instruction for initial setting from the external terminal; and providing, by the controller, the image sensors with the external instruction regarding lighting, wherein when an image sensor among the image sensors receives the external instruction regarding lighting from the controller, the image sensor performs lighting control in accordance with the external instruction regarding lighting on a luminaire among the luminaires to determine (i) a relative position of the luminaire relative to the image sensor, and (ii) a relative position of the image sensor relative to a different image sensor among the image sensors, and determining, by the controller, positions of the image sensors and positions of the luminaires by collecting the relative positions of the image sensors and the relative positions of the luminaires determined by the image sensors.