The most common and most likely answer to this crossword clue is the 7 letter word AURORAE
I've seen this crossword clue in The Guardian
A
U
R
O
R
A
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Buddy explains!
The straight part
We know that "light displays" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case light displays = aurorae.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 AURORAE mean?
AURORAE noun- An atmospheric phenomenon created by charged particles from the sun striking the upper atmosphere, creating coloured lights in the sky. It is usually named australis or borealis based on whether it is in the Southern or Northern Hemisphere respectively.