The PBM in action, at zenith, during dusk.

Observing was done from the city of Stockholm. During the data acqusition the sky was clear. The local astronomical twilight ended at 20:55 (18:55 UT), with the Sun at -18  degree altitude. The light-pollution from the city is obvious. At an excellent site, one could expect a LED current of 8 to 9 uA at astronomical night.

The twilight graph