A method of recording automatically spectral sensitivity of photoelectric surfaces has been developed. It consists of a Hardy spectrophotometer supplied with attachments for 60-cycle modulation of two glow discharge lamps. One of the lamps, serving as light intensity reference source, is supplied with an iris whose aperture is controlled mechanically by the analyzer cam. The other lamp is controlled photoelectrically so that its light intensity is proportional to the relative spectral sensitivity of the investigated photoelectrical surface. Light emitted by both lamps is received by the detector photo-tube which by means of thyratrons controls the recording mechanism.
J. T. TYKOCINER and L. R. BLOOM, "An Automatic Recorder of Spectral Sensitivity of Photoelectric Surfaces," J. Opt. Soc. Am. 31, 689-692 (1941)