The most common and most likely answer to this crossword clue is the 8 letter word SCREW-IN
I've seen this crossword clue in The Guardian
S
C
R
E
W
-
I
N
Buddy explains!
The straight part
We know that "This will shed light/l" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case this will shed light/l = screw-in.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.