Lyα escape fraction vs. f_c for various values of N_HI,cl, τ_d,cl = 1 and τ_d,cl = 10^-4 (filled and unfilled symbols, respectively). The black (gray) curves show some analytic curves for τ_d,cl = 10^-4 [τ_d,cl = 1]. The solid curve shows the Hansen & Oh (2006) formula as given by Eq. (18), the dashed line is the escape fraction from a homogeneous slab with N_HI = 4/3f_c10²² cm^-2 as given by Neufeld (1990), and the dotted line is simply exp(−4/3f_cτ_d,cl), symbolizing a continuum escape fraction.