Filling-factor dependence of the XUV spectrum. Left: spectral energy flux at 1 au for f_* = 0.01 (orange, solid), f_* = 0.1 (green, dashed), and f_* = 1 (blue, dotted). Centre: energy-flux ratio of f_* = 1 to f_* =0.01. Right: photon-number luminosity spectrum for f_* = 0.01 (orange, solid), f_* = 0.1 (green, dashed), and f_* = 1 (blue, dotted). Bottom panels are the same as top panels but with logarithmic x axis thatemphasise the short-wavelength region. For better visualisation, spectra are averaged over 20 Å-bins in the top panels.