NMAC INVOLVING AN MDT AND AN SMA AT NIGHT.

Narrative

DURING IDLE PWR DSCNT INTO DAB (NON TCASII ACFT) DAB APCH RPTED 'TFC AT 12 O'CLOCK; 1 MI; ALT UNKNOWN.' WE SCANNED THE AREA AND ALMOST IMMEDIATELY PICKED UP TFC. HOWEVER; IT WAS EXTREMELY DIFFICULT TO DETERMINE THE EXACT POS OF THE ACFT AS THERE WAS A TALL TWR ON THE GND WITH FLASHING STROBES ALIGNED SO THAT THE SMALL PLANE CAME OUT OF THE LIGHTS; SO TO SPEAK. SINCE THERE WAS ONLY 5-6 SECONDS BTWN THE TA AND THE NEAR MISS; THERE WAS NO TIME TO REQUEST A TURN AWAY FROM THE TARGET. AS WE WERE IN A DSCNT WHEN WE VISUALLY ACQUIRED THE SMALL PLANE IN THE COPLT'S FORWARD WINDOW I JUST PUSHED THE ACFT NOSE OVER. WE MISSED HIM BY AN ESTIMATED 200-500 FT. ALL PAX WERE IN THEIR SEATS WITH BELTS FASTENED. NO ONE WAS INJURED AND NO DAMAGE DONE. ATC WAS NOT TALKING WITH THE ACFT. ATC RPTED TO US AFTER THE INCIDENT THAT HE HAD JUST SUDDENLY SEEN A PRIMARY TARGET IN OUR POS. THE ACFT APPARENTLY HAD NO TRANSPONDER; OR WAS NOT USING ONE. TCASII AND ENCODING TRANSPONDERS/ALTIMETERS IS THE ONLY WAY TO PREVENT THIS TYPE OF SITUATION. SUPPLEMENTAL INFO FROM ACN 206498: AFTER THANKING APCH FOR THE 'HEADS-UP' CALL; HE EXPLAINED THAT THE VFR ACFT HAD CHKED ON DAYTONA APCH (NOT OUR FREQ) JUST PRIOR TO HIS CALLING HIM TO US; AND THAT HAD HE NOT HE MAY NOT HAVE NOTICED HIS PRIMARY TARGET.