Leaves one in the dark if it makes one happy (8)
I believe the answer is:
delights
'leaves' is the definition.
Although both the answer and definition are verbs in their -s form, I can't see how one could define the other.
'one in the dark if it makes one happy' is the wordplay.
I cannot really understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for delights that I've seen before include "Pleasures; pleases" , "Transports" , "Slighted by pleasures" .)