one of our night sky spectra, taken on the 1st of February 2012. For comparison also laboratory spectra of common street lamps are shown. The strongest spectral line that we detect in the light-polluted night sky over Vienna is located at 546nm. An adjacent, but weaker line is detected at 544nm. Both lines are due to fluorescent lamps (FL), which are currently the most common type of lighting, especially in residential areas.

The second strongest spectral feature that we find in our night sky spectra is centered at 611nm. Its origin is a composite of fluorescent lamps and high pressure sodium (HPS) lamps, which are used to illuminate suburban highways, crossroads and main streets. Between these two strongest spectral peaks, a series of lines are detected, most of which can be identified as sodium lines (outstanding peaks at 569nm, 588nm and 593nm). Another sodium line is detected in the photographic infrared, at 819nm. Since low-pressure sodium lines are uncommon in and around Vienna, the sodium peaks must be due to scattered light from high pressure sodium (HPS) lamps. More detailed information on the emission lines of HPS lamps can be found in Elvidge et al. [@Elvidge2010].

Furthermore, atmospheric absorption bands 