The last described device for long-term measuring of the night
sky is astronomical instrument (Sky quality meter), which
evaluates the luminances of the night sky. This instrument does
not work with lighting units (cd/m2), but in magnitudes (mag).
For traditional reasons, astronomers use the term magnitude,
expressed in units called magnitudes. Magnitude is a logarithmic
value. This instrument is able to compare the astronomical
measurements and lighting ones.