Top panels: synthetic EUV irradiance spectrum (black line) convolved with a 1-Å boxcar calculated for the feature QS1, along with the passbands of the EIT 171 Å (left panel, red dotted line) and 195 Å (right panel, blue dashed line) channels (in arbitrary scale). Bottom panels: the left panel shows the irradiance spectra for QS1 (black), QS2 (blue), AR1 (green), AR2 (orange), and AR3 (red). The right panel gives the ratios of the synthetic spectra for each component to the QS1 spectrum. The EIT 171 Å and 195 Å passbands are indicated again.