A CPR DA20 FLC HAD A LIGHT BULB FAILURE AND DID NOT GET A GREEN LIGHT ON THE L MAIN LNDG GEAR; BUT AFTER THE TWR CTLR CHKED THE GEAR POS VISUALLY AND THE FLC RAN THEIR CHKLISTS AND THEN LANDED WITHOUT FURTHER PROB. THE BULB WAS REPLACED AFTER TELEPHONE CONSULTATION WITH THEIR MAINT BASE.

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ON L BASE TO RWY 5 LNDG GEAR WAS SELECTED DOWN AND ONLY 2 GREEN LIGHTS WERE VIEWED (NOSE AND R MAIN) CYCLED LNDG GEAR ONCE AND PROB REMAINED. PERFORMED LIGHT BULB TEST AND L MAIN BULBS APPEARED TO BE OUT. REQUESTED GAR VIA THE TWR AND EXPLAINED OUR SIT. THE TWR VERIFIED 3 GEAR DOWN AS WE FLEW BY AND THEN OFFERED TO MAKE REQUEST FOR SAFETY EQUIP TO BE STANDING BY WHICH WE AFFIRMED. IN THE TFC PATTERN THE CHKLIST ITEMS WERE PERFORMED AND ACFT WAS LANDED WITHOUT INCIDENT. ON THE GND OUR MAINT DEPT WAS CONSULTED VIA CELLULAR PHONE FROM COCKPIT FROM WHICH WAS DETERMINED THE TYPE OF BULB NEEDED AND PROCESS OF CHANGING BULB FOR WHICH WE HAD SPARES ONBOARD. THE BULB WAS CHANGED AND RECHKED; ALL OKAY. I COMPLETED A DISCREPANCY FORM AND SIGNED IT OFF. WE THEN DEPARTED XA34 FOR NEXT DEST TEB AND LANDED UNEVENTFUL. AN FAA INVESTIGATION BEGAN IMMEDIATELY FOLLOWING THE SIT BY THE FAA INQUIRING OF OUR WHEREABOUTS TO THE LYNTON JET FBO; MMU OF WHICH I HAPPENED TO BE TALKING TO ON THE PHONE FROM TEB ABOUT AN UNRELATED MATTER AND WAS PLACED ON THE PHONE WITH THE FAA. I ANSWERED THEIR QUESTIONS BUT WOULD NOT GIVE MY NAME OR CERTIFICATE NUMBER BECAUSE I WAS UNSURE OF THEIR IDENTS. THE FOLLOWING DAY AT TEB THE FAA CONDUCTED AN INVESTIGATION AND PERFORMED A RAMP CHK. THE FAA INFORMED US THAT THE INVESTIGATION WOULD CONTINUE AND WE WOULD BE NOTIFIED ANY WRONG DOING. THE IMPLICATION WAS MADE THAT I WAS NOT AUTH TO PERFORM A PERCEIVED MAINT FUNCTION (CHANGING A LNDG GEAR LIGHT BULB). OUR CORPORATION OPERATES UNDER PART 91 AND ALL TRIPS ARE PART 91. THE FAA INVESTIGATOR TALKED WITH OUR DIRECTOR OF MAINT AND MENTIONED MATTER WAS DEAD AS FAR AS ENFORCEMENT.