A light assembly that includes a mounting frame on which a light engine is mounted so as to direct light through the mounting frame opening and out of an opening in the ceiling. The closed state and the opened state of the keyboard are detected, and operation of one of the apparatus main unit and the keyboard is controlled according to a detection result. The control circuit includes a compensation device adapted for cancelling the thermal variation of the signal that is representative of the current signal flowing in the MOS transistor.