Unlike　short　circuit　faults　in　power　systems,　arcing　faults　produce　intense　light　during　the　events.　Light　sensing　technology　has　been　developed　as　a　part　of　arc　faults　detection　since　1980＇s.　Currently,　optical　fiber　and　point　sensors　are　2　types　of　light　sensors　which　have　been　applied　along　with　simultaneous　over-current　mechanism　for　arc　flash　relays.　Due　to　the　characteristics　of　light　sensors,　sensitivity　and　reliability　of　the　relay　may　be　affected　by　the　ambient　light.　This　paper　proposes　a　new　approach　for　arc　flash　fault　detection　by　using　spectrum　of　the　light.　Electromagnetic　radiation　means　different　element　would　emit　spectra　with　unique　wavelengths　when　their　atoms　are　excited.　Therefore,　elements　can　be　identified　if　specific　emission　spectrum　are　detected　during　the　excitation　period.　In　general,　Copper　and　Aluminum　are　commonly　used　for　conductors.　By　examining　the　spectrum　of　the　light,　arc　flash　can　be　accurately　and　quickly　detected.　In　the　experiment　of　this　study,　copper　and　aluminum　are　applied　as　conductors.　The　light　spectrum　for　both　materials　are　measured　and　recorded　by　an　optic　spectrometer　during　the　arcing　incidents.　The　results　show　that　accuracy　and　reliability　of　the　light-based　arc　flash　fault　detection　operation　can　be　improved　by　using　the　proposed　method.　©　2018　IEEE.