The quantity E_s is shown in the top panel for both figures, the SCALA relative light output from the commissioning in May 2014 is in blue and the latest commissioning in May 2015 is in red. Both are normalized to their average values to compare only their color trend. One of the mirrors illuminated by the same IS as the reference for the 2015 SCALA relative efficiency measurements, normalized by its average value, is shown using solid black circles. Bottom panels: ratios between the two sets of commissioning measurements. The dashed lines represent the ±1% range around the averaged value computed for the measurements from 4700 Å to 10 000 Å, where a gray offset is present. The full line, around 0.995, is the average and the dotted lines span the standard deviation interval (±0.005). The quantities in the left panel refer to E_s measured with the Xe lamp while the right panel shows the measurements with the halogen lamp.