Light on (blue)
Some reason for new nighttime illumination is suburban growth rings around existing urban centers, newly built transportation lines, the electrification of rural areas, or wellhead fires at new petroleum extraction sites.
Light out (magenta)
Some reasons for extinguished nighttime illumination are the collapse of population or infrastructure due to war or social upheaval, the contraction of populations from economically struggling areas, or preventative measures taken to reduce nighttime light pollution.
Source: John Nelson (AdventuresInMapping.com)