A solar irradiance photometer was launched on a pair of ESRO Centaure rockets. The instrument, a solar irradiance photometer used six wavelength channels. Three of these channels were used to measure meso-spheric ozone by the occultation method. Two other channels were equipped with 214-nm Fabry-Perot filters to monitor the absorption of sunlight required for the excitation of NO gamma-band fluorescence, which was measured by another instrument in the same payload. One of the 214-nm channels used a quartz lens, while the other used a glass lens. With a glass-quartz chopping technique, stray light with wavelengths longer than 300 nm could be eliminated. Since ozone is absorbing at 214 nm, these two channels were also used for measuring mesopheric ozone. By comparing the ozone measurements from the two 214-nm channels with the measurements from the three channels intended for ozone measurements, one can obtain the performance of the glass-quartz chopping method.