The present invention relates to a method of controlling a dimmable luminaire co-arranged with a light sensor at a first level of a room and illuminating a second level of the room, comprising: determining an output path parameter representing a relation between the amount of light emitted from the luminaire and a luminaire illumination value at the second level, which results from the emitted amount of light; and repeatedly: determining an external illumination value at the second level, which external illumination value represents illumination by other sources than the luminaire, by means of values of the presently emitted amount of light, the output path parameter, and light information originating from the light sensor; and controlling the dimming level of the luminaire on basis of the external illumination value in order to meet a predetermined illumination condition for the total illumination at the second level.