Lyα spectra emerging from clumpy spherical shells with non-unity coverage. Left: expanding shell with fiducial values of the parameters (v_exp = 150 km s^-1, log(N_HI) = 20, b = 20 km s^-1, E(B − V) = 0.1). Right: static shell with exactly the same values of the parameters, except the velocity field, which is set to zero. In both cases, the intrinsic spectrum is a continuum plus a Gaussian emission line of FWHM = 100 km s^-1 and EW = 100 Å (red dotted line). The black lines shows the global emerging spectra, spatially integrated over the whole shell. The blue and green lines are a decomposition of the black curves in photons that escaped without scattering (nb_diff = 0, blue) and photons that interacted before escape (nb_diff> 0, green). This second packet of photons is compared to the result of Lyα radiation transfer in a homogeneous shell (orange curve). These spectra are convolved with a Gaussian to mimic an instrumental resolution of R = 4000. The main features in the Lyα spectra that emerge from transparent lines of sight in riddled ionisation-bounded H ii regions are v_peak = 0 and, as a consequence, a non-zero flux bluewards of the systemic redshift.