Comparison between three profoundly different spectral faces of the Sun, for the spectral window 4223–4231 Å around the strong Ca i 4227 Å line. Top panel: SS1 (the intensity spectrum) for μ = 1.0. Middle panel: SS3 (the limb/disk-center ratio spectrum R) for μ = 0.145. Bottom panel: SS2 (the Second Solar Spectrum) for μ = 0.1 with the level of the continuum polarization drawn as the horizontal dashed line.