Abstract: The light output of a multi-lamp lightfastness testing chamber defining a sample testing area in the chamber may be performed by sequentially turning on and off each lamp by itself, while measuring from the sample testing area the irradiation provided by each lamp, while adjusting the intensity of irradiation for each lamp to a desired level. Thereafter, individual lamp sensors (56) sense the light intensity of each individual lamp. Typically by a feedback circuit, the power to each lamp is adjusted so that the sensed light intensity of each lamp is maintained within predetermined limits corresponding to the irradiation level measured from the sample testing area.

Abstract: A lightfastness testing chamber comprises an enclosure for samples being tested and at least one, and preferably a plurality of, lamps for irradiating samples in the enclosure. A monitor of the light intensity from each lamp present is provided. By this invention the monitor may comprise a light transmission rod, and preferably one such rod for each of the lamps, having one end positioned adjacent the lamp and another end in communication with light intensity measuring apparatus positioned more remotely from the lamp than the one end. The light transmission rod is preferably positioned on a side of the lamp that is substantially opposed to portions of the lamp that directly irradiate samples in the enclosure. Also, the samples may be moved by an elevatable platform or the like toward and away from the irradiating lamp or lamps to vary as desired the intensity of irradiation applied to the samples.