Distribution of emission-line fluxes measured for the brightest emission-lines versus redshift for the 21 sources found behind A1689, with and without correction for lensing magnification. The lines used are given in Col. 3 of Table 2 (Lyman-α at z ≥ 3). The horizontal dashed line indicates the median lens-corrected flux value. Multiply imaged sources are counted once in this diagram.