Linear polarization efficiency as function of the normal albedo at 1° (Eq. (9)) for the B (dashed), V (dash-dot), R (solid), and I (dash-dot-dot) band. More information about the fit procedure to the Hapke et al. (1993) samples in the red (⋄) and the blue (+) is given in the text. Measurements of the same sample are connected by dotted lines. The thick black lines show the derived wavelength and albedo-dependent polarization efficiencies for our two measurement areas #1 and #2 (Fig. 6).