Source of light comes from saint’s apparel (6)
I believe the answer is:
strobe
'source of light' is the definition.
'strobe' can be an answer for 'light' (strobe light is a type of light). I'm not certain of the 'source of' bit.
'saint's apparel' is the wordplay.
'saint' becomes 'st' (abbreviation).
'apparel' becomes 'robe' (robe is a kind of apparel).
'st'+'robe'='STROBE'
'comes from' is the link.
Can you help me to learn more?
(Other definitions for strobe that I've seen before include "Sort of lighting" , "Flashing lamp" , "Flash on and off" , "Flashing, very bright beam" , "something flashy" .)