PURPOSE: To automatically monitor the deterioration in the illuminance of an illumination lamp, by monitoring the lowering in the illuminance of the lamp by providing the reflecting shade of the lamp, the optical fiber attached to the reflecting shade and an illuminance sensor having the separate terminal of the optical fiber as input.

CONSTITUTION: An optical fiber 3 is attached to the inside of a reflecting shade 2. The open end of the fiber 3 is fixed so as to be directed to the lamp 1 and receives the light emitted from the lamp 1 to allows the same to transmit through the fiber 3. Two or more fibers are arranged to one lamp. If one fiber is attached to the shade of the lamp, an illuminance detected by the fiber changes by a factor other than the deterioration in the illuminance of the lamp such as backlash. In order to prevent this defect, two or more fibers are incorporated in the shade of the lamp. A drawing shows such a state that two fibers are incorporated in the shade of the lamp and, by taking the averaging of the outputs of the fibers, the deterioration in the illuminance of the lamp can be determined accurately.