Spectra of the total energy output of the fiducial stellar population (i.e., N = 10 ⁶, Kroupa IMF, f _sur = 1) after 5, 50, 100, and 150 Myr (solid, long-, medium-, and short-dashed curves, respectively). The spectral shape derives from the stellar UV blackbody and the HMXB softer blackbody + harder power-law component, where we use the spectrum of Cygnus X-1 for our HMXB template.