A B737-300 FLT CREW ON FINAL APCH EXTENDED THE LNDG GEAR AND HAD NO LNDG GEAR SAFE OR UNSAFE LIGHTS. CREW DISCOVERED AN OPEN CIRCUIT BREAKER.

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WE WERE AT 2000 FT MSL ON A VISUAL TO RWY 16L AT SMF DURING DAY VMC. WINDS WERE OUT OF THE S AT 14 KTS. WE WERE CONFIGURED WITH FLAPS 5 DEGS AND THE GEAR WAS UP. APCHING 1 DOT BELOW GS; I CALLED FOR GEAR DOWN AND FLAPS TO 15 DEGS. AT APPROX 1500 FT MSL I CALLED FOR FLAPS 30 DEGS AND THE BEFORE LNDG CHKLISTS. AS I LOOKED AT THE GEAR/FLAP INDICATORS; I NOTICED THAT THERE WERE NEITHER GREEN NOR RED LIGHTS ILLUMINATED FOR THE GEAR. I BROUGHT THIS TO THE CAPT'S ATTN AND HE PERFORMED A 'PTT' ON THE LIGHTS. NONE OF THE LIGHTS ILLUMINATED. WE PERFORMED A LOW APCH AT 500 FT AGL AND TWR SAID OUR GEAR APPEARED DOWN. WE DID A GAR AND WERE GIVEN A CLB TO 2000 FT MSL AND A TURN TO THE N. WE LEFT THE GEAR DOWN AND THE FLAPS AT 15 DEGS. WITH THE AUTOPLT ENGAGED; THE CAPT TOOK CTL OF THE ACFT AND I CONFIRMED THAT THE GEAR WAS DOWN AND LOCKED BY VIEWING THEM THROUGH THE VIEWING PORTS. AFTER I STRAPPED BACK INYO MY SEAT; WE RAN THE QRH AND FOUND THE 'SECTION 5' CIRCUIT BREAKER BEHIND MY SEAT WAS POPPED. AFTER RESETTING THE CIRCUIT BREAKER; WE IMMEDIATELY NOTICED 3 GREEN LIGHTS. ONCE ALL QRH PROCS WERE COMPLETE; I WAS GIVEN CTL OF THE ACFT BACK. WE PROCEEDED TO GET VECTORS FOR ANOTHER VISUAL APCH TO RWY 16L. THE REST OF THE APCH AND LNDG WERE UNEVENTFUL.