Illumination items: By the lighting and illumination committee

It is a fact well known to lighting men that the amount of illumination obtained from lighting equipment decreases gradually but surely with length of service, due to dust and dirt which accumulate on the surfaces of the lamp and the reflector. A few months ago an investigation was undertaken to classify the kinds of dirt which may be expected to accumulate on the lamps in representative industries and to determine just how much the light output of lamps may be increased by removing these dirts.