can be identified at 762nm (A band) and 688nm (B band) due to magnetic dipole electronic transitions of the molecule O$_2$ ([@Kiehl1985]).

   Peak position \[nm\]   Assignment (see text)       Remark
  ---------------------- ----------------------- ----------------
           544                     FL            
           546                     FL            
       569/588/598                 HPS           
           611                     FL             blend with HPS
           819                     HPS           

  : Selected (strong) spectral lines detected in Vienna’s night sky.

\[t:spectrallines\]

![ Night sky spectrum (filled area) obtained in Vienna on February 1st, 2012 towards SE. It can be clearly seen that the most prominent features correlate with emission lines originating from FL (blue solid line) and HPS (orange solid line). Laboratory spectra of street lamps can be found on the website of the National Oceanic and Atmospheric Administration [@NOAA].[]{data-label="fig:skyspectrum"}](Figure9.eps){width="13cm"}

According to the official statistics of the city of Vienna, 80% of all the lamps used for public illumination are fluorescent lamps, 16% are HPS, while other types of lamps add up to only 4% by number. This is in good accordance with our spectroscopic results.

The total power used for street lighting in Vienna amounts to 14 MW (value from the official website <http://wien.gv.at> [@WIEN]. Assuming a lumen-to-Watt ratio of 70 for fluorescent lamps and 120 for HPS, we end up with a contribution 