What was found
ON APPROACH, EXTENDED MLG AND LT MLG LIGHT FAILED TO ILLUMINATE GREEN. ABORTED APPROACH. ON COMPLETION OF CHECKLIST. INCLUDING BLOWING THE NITROGEN BOTTLE, ROTARY TEST & FAILURE OF LIGHT TO ILLUMINATE, DECLARED AN EMERGENCY. AFTER SUCCESSFULLY COMPLETING MLG WARNING HORN TEST CONFIRMING A BAD BULB. ACFT LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED BULB IN DOWN INDICATOR. SATISFACTORY GEAR SWING WAS PERFORMED, ACFT FLEW SUCCESSFUL OPS CHECK FLT AND WAS RETURNED TO SERVICE.