Mock spectra synthesised from the z = 3 snapshot with a QSO in a filament. The QSO sits on the right hand side of each spectrum, and the wavelength is in Ångström. The dashed line gives the Lyα forest spectrum without the influence of the QSO, the solid line the spectrum from the radiative transfer simulation of the proximity effect for a QSO with a Lyman limit luminosity of L_νLL = 10³¹   erg   Hz^-1   s^-1. The spectra have a resolution of Δv = 6.7   km   s^-1 and a signal-to-noise ratio of 70.