The iodine atmosphere in typical quartz-iodine lamps modifies the spectrum of the emitted light by selective absorption in a broad band in the green-yellow region. Results of a study of the spectral emission of a series of quartz-iodine lamps with different amounts of iodine are given.
F. J. STUDER and R. F. VANBEERS, "Modification of Spectrum of Tungsten Filament Quartz-Iodine Lamps due to Iodine Vapor," J. Opt. Soc. Am. 54, 945-947 (1964)