Weighted average of the line intensity normalized to the line intensity of the line in the 9 mA spectrum of the four data subsets: 258 confirmed U lines (blue squares) and 194 confirmed Ne lines (red squares), 525 U lines candidates with a match in the 6, 9, and 12 mA spectra (light brown diamonds), and 1533 U line candidates identified only in the 9 and 12 mA spectra (brown diamonds). The error bars indicate the weighted standard deviation. The red and blue dashed lines indicate the approximate trend that follows the normalized averaged intensity of the buffer gas and the cathode lines, respectively.