We report on our recent detection of the transverse proximity effect of 4 foreground quasars near Q 0302 - 003 ( z = 3.285 ) as a local hardness fluctuation in the spectral shape of the intergalactic UV radiation field , found by correlating the H I Ly \alpha absorption with the corresponding He II Ly \alpha absorption .
We argue that the spectral hardness is a sensitive physical measure to reveal the influence of quasars onto the UV background over scales of several Mpc , and that it breaks the density degeneracy hampering the search for the elusive transverse proximity effect .
From the transverse proximity effect on scales of several Mpc we obtain minimum quasar lifetimes of \sim 10–30 Myr .