AN ACR ACFT ON VISUAL APCH AT NIGHT TO BUR SEES WRONG ARPT AND DSNDS BELOW THE MVA.

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I WAS WORKING ARRS LATE AT NIGHT INTO BURBANK ARPT. ACR #1 CHKED IN 22 MI N OF THE ARPT IFR AT 8000 FT. ACR #1 REQUESTED A VISUAL APCH TO RWY 15. I VECTORED ACR #1 TO A POINT 12 MI NW OF THE ARPT AND DSNDED THE ACFT TO 5000 FT; THE MVA IN HIS AREA. THE ACFT RPTED THE FIELD IN SIGHT; AND I CLRED HIM FOR THE VISUAL APCH. AT ABOUT 8 MI OUT I WENT BACK TO ACR #1 TO SHIP HIM TO THE TWR. THE ACFT SAID HE HAD 'LOST THE ARPT;' BUT HE WAS STILL DSNDING. I STOPPED THE ACFT'S DSCNT AND VECTORED HIM HDG 110 DEGS FOR THE ARPT. THE ACFT SAID HE WOULD LEVEL OFF AT 3000 FT. HE WAS JUST LEAVING A 5000 FT MVA AND ENTERING A 4000 FT MVA. I MADE A XMISSION TO ANOTHER ACFT AND WHEN I LOOKED BACK AT ACR #1; HE WAS DSNDING OUT OF 2600 FT AND HEADING S. I CANCELED HIS APCH CLRNC AND CLBED THE ACFT ABOVE THE MVA. IT APPEARED THAT ACR #1 HAD GOTTEN WHP ARPT IN SIGHT AND WAS HEADING FOR WHP. ON REFLECTION I SHOULD HAVE CANCELED ACR #1'S APCH CLRNC WHEN HE INITIALLY LOST SIGHT OF BUR. MY THINKING AT THE TIME WAS HE SHOULD PICK THE ARPT BACK UP VISUALLY FAIRLY QUICKLY AND ALTHOUGH THE MVA IS 4000 FT IN HIS AREA; I KNOW IT IS SAFE ON THE HDG I GAVE THE PLT. IF I HAD AN ARR ON THE ILS TO RWY 8; THERE IS NO WAY I COULD HAVE KEPT STANDARD SEPARATION FROM ACR #1.