[en] We investigate the temperature-dependence of the light emission properties of Cu-dominated plasmas with pressures in the order of 1 bar and for currents between 0 and 2 kA. While the wavelength of Cu I 3d⁹4s5s transitions for currents above 1 kA is essentially constant, a 0.1 nm Stark blueshift is observed with decreasing current from 1 kA to zero. Using a lineshape analysis of the light emission spectra, which is based on solving a one-dimensional radiative transfer equation along the line-of-sight across the arc, we show that the transition wavelength increases linearly with temperatures in the 5000–10 000 K range. Based on this observation, we propose a simple method for the temperature diagnostic of plasmas that neither requires an absolute calibration of the intensity of the detected signal, nor complex simulation tools. (paper)