What was found
LEFT ENGINE START AT GATE, ALL PARAMETERS NORMAL, UPON PUSHBACK PAX ALERTED FLIGHT CREW THAT SMOKE HAD FILLED THE CABIN. CREW SHUTDOWN LT ENGINE AND SOON AFTER SMOKE HAD CLEARED. RAN NO SMOKE NOTED FOR 10 MIN. WALK THROUGH CABIN FOUND NOTICEABLE SMOKE ODOR ABOVE CEILING AREA STARTING FROM ROWS 30 AND AFT. ODOR SIMILAR TO BALLAST TYPE. RT LAST ROW SIDE WALL LIGHT INOP. REPLACED LIGHT ASSY AND RELAMPED OPS CHECKED OK. NR 2 LT DOOR CEILING LIGHT INOP. REPLACED BALLAST AND RELAMPED, OPS CHECKED OKAY.