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Figure 2 shows an overview of the spectrum covering the range 715 nm to 5000 nm (14000 cm−1 to 2000 cm−1). Beyond 2500 nm, continuum emission from the hot cathode becomes noticeable (Figure 2). Its intensity is strongly dependent on the operating current, but at all currents it is much weaker than the spectral lines and thus accurate wavenumbers for the lines could be measured. Test spectra recorded from a lamp with a see-through hollow cathode had a much lower continuum, but the overall intensity and signal-to-noise ratio in these spectra was also much lower.