The most common and most likely answer to this crossword clue is the 8 letter word HALATION
I've seen this crossword clue in Financial Times
H
A
L
A
T
I
O
N
Buddy explains!
The straight part
We know that "Foggy effect" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case foggy effect = halation.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.
What does HALATION mean?
HALATION noun- The action of light surrounding some object as if making a halo.
- The blurring of light around a bright area of a photographic image, or on a television screen.