Type of light lake punt Royal Navy pursues (7)
I believe the answer is:
lantern
'type of light' is the definition.
'lake punt royal navy pursues' is the wordplay.
'lake' becomes 'l' (geographical abbreviation).
'punt' becomes 'ante' (anteing is a kind of punting).
'royal navy' becomes 'RN' (abbreviation for Royal Navy).
'pursues' is a charade indicator (letters next to each other).
'l'+'ante'+'rn'='LANTERN'
(Other definitions for lantern that I've seen before include "Transparent case for holding a light" , "Light in a protective casing" , "It illuminates" , "Enclosed light" , "Light in a transparent protective case" .)