Iron edges of light fabric (4)
I believe the answer is:
felt
'fabric' is the definition.
(I know that felt is a type of fabric)
'iron edges of light' is the wordplay.
'iron' becomes 'Fe' (chemical symbol for iron).
'edges of' says to hollow out the word (remove centre letters).
'light' with its centre taken out is 'lt'.
'fe'+'lt'='FELT'
(Other definitions for felt that I've seen before include "Touched the carpet underlay" , "Cloth of pressed wool and fur" , "Touched the matted fabric" , "Baize-like cloth" , "Cloth of matted fibres; experienced" .)