B737 FLT CREW ENCOUNTERS FAILURE OF LNDG GEAR WARNING LIGHTS ON LNDG.

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ON ILS APCH TO RWY 25L AT ZZZ; WHEN GEAR HANDLE LOWERED; NO GEAR DOWN AND LOCKED INDICATIONS. HAD RED NOSE GEAR LIGHT ONLY. CHKED CIRCUIT BREAKERS; AS DID THE FO; AND ALL WERE IN. CHK LIGHTS TEST AND ALL LIGHTS TESTED EXCEPT L MAIN -- NEITHER LIGHT WORKED. REPLACED BULBS IN SAME AND STILL LIGHTS DID NOT TEST. FO COMPLETED MANUAL GEAR EXTENSION CHKLIST AND WENT TO CABIN TO CHK VIEW PORTS OF MAINS AND THE NOSE VIEW PORT IN THE COCKPIT. DID THE LIGHTS TEST IN BRIGHT AND DIM POS. PRIOR TO THIS; WE MISSED AND FLEW DOWN RWY FOR TWR TO GIVE US A VISUAL. TWR SAID GEAR APPEARED TO BE DOWN. DECLARED AN EMER; BRIEFED DISPATCH; MAINT; OPS; AND FLT ATTENDANTS AND PAX ON SIT. TOLD PAX THAT I BELIEVED THE GEAR WAS DOWN; BUT THAT WE WERE GOING TO HAVE FLT ATTENDANTS BRIEF EMER LNDG PROCS AND HAVE THE EMER EQUIP STANDING BY AS A PRECAUTION. NORMAL LNDG AND ROLLOUT. TAXIED CLR OF RWY AND HAD LINE PIN GEAR BEFORE WE TAXIED TO GATE FOR NORMAL DEPLANING. AFTER LNDG; THE GEAR SENSING/LIGHT CIRCUIT BREAKER POPPED; CREATING NORMAL INDICATIONS THAT ACFT WAS STILL AIRBORNE. BIGGEST DISTR AND WORKLOAD WAS WHEN FO LEFT COCKPIT TO CHK VIEW PORTS. AUTOPLT WAS USED TO MANAGE WORKLOAD. IT WAS A MECHANICAL ISSUE. FO AND FLT ATTENDANTS DID SUPER JOB.