A glass object allowing some light in? (4)
I believe the answer is:
ajar
'allowing some light in?' is the definition.
'a glass object' is the wordplay.
'glass object' becomes 'jar'.
'a'+'jar'='AJAR'
(Other definitions for ajar that I've seen before include "near closing?" , "A little bit open, like door" , "Partially open" , "(Of door) slightly open" , "Half open" .)