A high-pressure scanning tunneling microscope (STM) unit was used to produce electrical discharges on a mesoscopic scale. Piezoelectric positioning elements allow to adjust the electrode gap with the precision needed. Optical emission spectroscopy was performed in high-pressure environments of helium and argon in a range of 5-20 bar. Spectra were recorded at different gas pressures and discharge currents. The increase of gas pressure changed line intensities and caused broadening of spectral lines of helium and argon. Increasing the discharge current yielded a higher intensity of the emitted light. The use of different electrode materials had no significant influence on the spectra. Electrical gas discharges on the microscopic scale can be used not only as a lithographic tool, but also as a compact light sourer of high luminance with emission of well-defined line spectra.