We demonstrate a static multiplex spectrometer based on a Fabry-Perot interferometric filter for measuring the
mean spectral content of diffuse sources. By replacing the slit of a low-dispersion grating spectrometer with
a Fabry-Perot interferometric filter, we improve the resolving power of the instrument while simultaneously
overcoming the free spectral range limitation of the Fabry Perot. The resulting instrument is smaller than conventional
spectrometers having the same resolving power. We present experimental results from the spectrometer
using neon lamp, He-Ne laser, and diode laser sources over a wavelength range from 620 nm to 660 nm.