What was found
ON APPROACH WITH LANDING GEAR HANDLE SELECTED DOWN, THE NLG DOWN (GREEN)INDICATOR FAILED TO ILLUMINATE. NO MASTER OR AURAL WARNING ASSOCIATED WITH ISSUE OBSERVED. FOLLOWED CHECKLIST, EMERGENCY DECLARED, DIVERTED TO TPA AND LANDING MANUAL EXTENSION PROCEDURE PERFORMED. LANDING WAS UNEVENTFUL. MAINTENANCE REPLACED THE DOWN AND LOCK ANNUNCIATOR LIGHT BULBS. GEAR SWINGS AND OPERATIONAL CHECK PERFORMED. NO DEFECTS NOTED. AIRCRAFT WAS RETURNED TO SERVICE.