Reason for fading light in part of Leinster? (7)
I believe the answer is:
wicklow
'part of leinster?' is the definition.
(county in the province of Leinster in Ireland)
I don't understand the remainder of the clue.
(Other definitions for wicklow that I've seen before include "Irish port, town, county" , "part of Ireland?" , "Irish county team" , "port buildings here in Ireland" .)