From Longman Dictionary of Contemporary Englishsnap on/off phrasal verbSWITCH ON OR OFFto switch something on or off, or to switch on or off A light snapped on in one of the huts.snap something ↔ on/off Kathy snapped off the light. → snap→ See Verb table
Examples from the Corpus
snap on/off• The light trained on his bed snaps off.• The satellite and more than 12 miles of tether linking it to Columbia snapped on Feb. 25.• His tormentors had snapped off the lights as they wished him goodnight, and it was completely dark. 