Disclosed is a controlling apparatus for a dimming level of a light disposed on a ceiling surface, including: a sampling unit sampling an illumination value of a ceiling area depending on a change in a dimming level of the light; a communication unit receiving an illumination value of a floor area at a minimum dimming level of the light and an illumination value of the floor area at a maximum dimming level of the light; an estimation unit estimating an illumination value of the floor area at a current dimming level of the light based on an algorithm defined by using the illumination value of the floor area and the illumination value of the ceiling area at the minimum dimming level of the light, the illumination value of the floor area and the illumination value of the ceiling area at the maximum dimming level of the light, and the illumination value of the ceiling area at the current dimming level of the light; and a control unit controlling the dimming level of the light so that the estimated illumination value of the floor area and a target illumination value coincide with each other.