DC10 CAPT DSNDED BELOW THE MSA DURING A VISUAL APCH DUE TO THE NIGHT LIGHTING CONDITIONS CAUSED HIM TO BELIEVE THAT HE WAS AT THE APPROPRIATE ALT DURING HIS 8 MI VISUAL APCH.

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ARRIVED IN THE TERMINAL AREA AND WAS VECTORED FOR AN ILS RWY 26. DISCONTINUED APCH DUE TO TSTMS ON FINAL APCH; ACCEPTED DELAY VECTORS; THEN WAS ADVISED RWY 33R WAS AVAILABLE. WHILE ENTERING APCH INTO THE FMS (FO FLYING); APCH CTL ASKED IF WE HAD A VISUAL ON THE ARPT. RWY WAS IN SIGHT ABOUT 8 MI AND WE WERE CLRED FOR A VISUAL APCH; ILS TO RWY 33R NOT WORKING (NO ELECTRONIC GS). RWY 33R HAS NO VASI; PAPI; ETC. WE APPEARED TO BE ON A 'NORMAL SIGHT PICTURE' FOR A VISUAL APCH WHEN TWR ADVISED OF A LOW ALT ALERT. I LEVELED OFF THE DSCNT RATE; RECOMPUTED A DISTANCE TO RWY VERSUS RADAR ALT; THEN RESUMED A CORRECTED VISUAL GLIDE PATH TO THE RWY. VECTORING IN THE LCL AREA; WX AVOIDANCE; LOADING MULTIPLE APCHS IN THE FMS (ILS RWY 26; THEN ILS RWY 33; THEN VOR 33) AND ATC COMS LED TO 'TASK SATURATION' AND A VISUAL DSCNT POINT WHICH BEGAN SLIGHTLY EARLIER THAN DESIRED. ALSO; THE 'DARK GND' BTWN OUR ACFT AND THE RWY PRODUCED THE ILLUSION OF BEING HIGHER THAN REQUIRED FOR THE OPTIMUM VISUAL GLIDE PATH. FROM HDOF FROM APCH TO TOUCHDOWN (WITH TWR) FLT CONDITIONS WERE NIGHT VMC; VISIBILITY APPROX 8+ NM.