Answer

The poem contrasts the outside and the inside. Inside the is the smell ‘tang’ of the ‘tiny oil lamp’ tang is a word that makes the smell seem a little strong on the nose and although not totally unpleasant, is not a pleasant smell.

Outside the lighthouse beam can be seen (line 2) and there is a feel of desolation. There is ‘the wind’.

Inside is ‘the sound of the wind’ ‘the locked heart and the lost key’
It is as if he feels frustrated about something, he cannot express his feelings.