What was found
UPON EXTENDING LANDING GEAR, PILOT OBSERVES NEGATIVE LEFT GEAR DOWN LOCK INDICATION. PILOT PERFORMS CURSORY TROUBLESHOOTING TECHNIQUES BUT COULD NOT VERIFY LEFT MAIN GEAR WAS POSITIVELY DOWN AND LOCKED. PILOT ULTIMATELY DECLARES EMERGENCY AT ALTERNATE AIRPORT AND PERFORMS EMERGENCY GEAR EXTENSION. MAINTENANCE PERFORMED AT ALTERNATE AIRPORT DETERMINED INDICATOR BULB WAS BURNT OUT. ALL 4 GEAR DOWNLOCK INDICATOR BULBS WERE REPLACED WITH NEW BULBS. EMERGENCY GEAR EXTENSION SYSTEM WAS RESET AND A FUNCTIONAL TEST OF LANDING GEAR WAS PERFORMED WITH NO DEFECTS NOTED.