Long-term measurements of night sky illuminance

The obtrusive light is understood as luminance of the night sky as well as any light that glares or radiates into locations where its is not desired and causes so called light overlap. Moreover this sort of light increases the energy losses. In this study we consider the increase of luminance of sky which causes sky glow that cause worse observation of stars. This is an obstruction mainly for astronomers but also for those who just like to observe the stars. We also published results of some measurements of illuminances under night sky in Ostrava city, in Czech republic.