PLT IMMEDIATELY DSNDED AND TURNED FROM ASSIGNED ALT AND DEP VECTOR IN RESPONSE TO SMOKE IN THE COCKPIT AFTER TURNING ON THE WINDSHIELD ANTI-ICING SYS.

Narrative

I DEPARTED PHX IN A C414 ON AN IFR FLT PLAN WITH 1 PAX. I WAS BEING RADAR VECTORED TO JOIN THE SID; CLBING TO AN INTERMEDIATE ASSIGNED ALT OF 13000 FT. I ENTERED THE CLOUDS AT APPROX 8000 FT AND NOTED THE OUTSIDE AIR TEMP APCHING '0' DEGS C. ANTICIPATING LIGHT ICING; I TURNED ON PROP ANTI-ICE AND WINDSHIELD ANTI-ICE. WITHIN 30 SECONDS; SMOKE STARTED COMING FROM THE LOWER L PORTION OF THE PLT'S WINDSHIELD. THE SMOKE WAS GOING DIRECTLY INTO MY FACE AND I FEARED BECOMING INCAPACITATED DUE TO WHAT SEEMED TO BE HIGHLY TOXIC SMOKE. I ADVISED ATC I NEEDED TO RETURN TO THE ARPT IMMEDIATELY DUE TO SMOKE IN THE COCKPIT AND STARTED A DSCNT TO GET TO VMC. THE SMOKE WAS INCREASING (NOW NOTICED BY THE PAX IN THE REAR CABIN SEAT) SO I TOLD ATC I REQUIRED THE NEAREST ARPT WHO THEN ADVISED THAT SDL WAS THE CLOSEST GIVING ME THE HDG AND DISTANCE. ABOUT THAT TIME; I NOTED THAT THE SMOKE WAS ORIGINATING FROM THE ELECTRICAL CONNECTION FOR THE WINDSHIELD HEAT SO I TURNED OFF THE WINDSHIELD ANTI-ICE. I WAS NOW DSNDING RAPIDLY IN VMC AND TURNING TOWARD PHX. THE SMOKE CEASED SHORTLY AFTER ELECTRICAL PWR WAS REMOVED SO I TOLD ATC I HAD THE SMOKE STOPPED AND WISHED TO RETURN TO PHX. ATC GAVE ME A VECTOR AND A DSCNT TO 4000 FT; ASKED IF I WAS DECLARING AN EMER AND IF I NEEDED THE 'EQUIP.' I ADVISED NO TO BOTH THE EMER AND THE EQUIP BECAUSE THE SMOKE HAD STOPPED AND NO STRUCTURAL DAMAGE WAS APPARENT. THIS WAS THE FIRST TIME I THOUGHT OF THE TERM 'EMER' EVEN THOUGH I HAD EXPERIENCE ONE. DUE TO THE GRAVITY OF THE SIT WHEN IT FIRST OCCURRED; I DSNDED FROM CLBING TO AN ASSIGNED ALT IN IMC WITHOUT THINKING OF DECLARING AN EMER. ALTHOUGH THERE WAS NO CONFLICT WITH OTHER ACFT DUE TO THE EARLY MORNING HR; THERE EASILY COULD HAVE BEEN. A DECLARATION OF AN EMER WOULD HAVE ALERTED ATC TO THE POSSIBILITY OF AN IMMEDIATE DSCNT AND CHANGE OF HDG. THE TIME SPAN OF THE INCIDENT FROM FIRST SMOKE TO THE ATC QUESTION REF AN EMER WAS LESS THAN 2 MINS AND LESS THAN 30 SECONDS TO GET TO VMC. AS TO CORRECTIVE ACTION: ON MY NEXT EMER SIT I WILL DECLARE SUCH AND ADVISE ATC OF MY INTENDED IMMEDIATE ACTION.