What was found
(CAN) DURING CLIMBOUT THROUGH 12,000 FT F/A REPORTED SMOKE IN THE CABIN. CREW STARTED TO TURN FOR AIRPORT. AT THIS POINT CREW DECLARED AN EMERGENCY FOR EXPEDITED ARRIVAL. ARFF MET ACFT TO DETERMINE IF RAPID DEPLANEMENT WAS REQUIRED. CREW DETERMINED IT WAS READING LIGHT AT SEAT 5F THAT SHORTED OUT AND SPARKED. NO FLAMES. ACFT TAXIED TO GATE. NO ADVERSE PAX REACTION. ACFT PLACED UNDER MEL AND CONTINUED TO MAINTENANCE BASE WHERE THE SIDEWALL LIGHT WAS REPLACED.