The Italian Light pollution institute has modeled the light pollution and night sky brightness from different parts of the world. http://www.lightpollution.it/dmsp/index.html
Credit: P. Cinzano, F. Falchi (University of Padova), C. D. Elvidge (NOAA National Geophysical Data Center, Boulder). Copyright Royal Astronomical Society. Reproduced from the Monthly Notices of the RAS by permission of Blackwell Science.
The colour coding in these maps is explained in the following paper.
An extract from the paper explains the colour coding:
An alternate way of understanding the colour coding: