The most common and most likely answer to this crossword clue is the 7 letter word AUREOLE
I've seen this crossword clue in The Times
A
U
R
E
O
L
E
Buddy explains!

The straight part
We know that "headlight" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case headlight = aureole.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 AUREOLE mean?
AUREOLE noun- A circle of light or halo around the head of a deity or a saint.
- (by extension) Any luminous or colored ring that encircles something.
- A corona.
- A ring around an igneous intrusion.