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