What was found
ON DESCENT FOR LANDING ON FLIGHT 3173, ONLY HAD 2 GEAR DOWN LIGHTS, AFTER GEAR EXTENSION. EXECUTED MISSED APPROACH OF RAN QRH, CHANGED BULBS, RECEIVED 3 GEAR DOWN LOCKED LIGHTS. 2 BULBS USED FROM BULB HOLDER. MAINTENANCE RESTOCKED BULBS. P/N 327.