What was found
FLT 632 - PHX-PIT - SMOKE - PRIOR TO LANDING, CABIN LIGHTS FLICKERING. UPON LANDING IN PIT, SMOKE WAS REPORTED IN THE CABIN (POWDERY SMOKE), SOURCE WAS AROUND ROW 4. CREW DECLARED EMERGENCY, FIRE AND RESCUE EQUIPMENT RESPONDED. INSTALLED NEW BALLAST. OPERATIONAL CHECK WAS GOOD.