The most common and most likely answer to this crossword clue is the 10 letter word HEADLIGHTS
I've seen this crossword clue in Financial Times
H
E
A
D
L
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More clues leading to the result HEADLIGHTS
Buddy explains!
The straight part
We know that "they could be turned on tonight" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they could be turned on tonight = headlights.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 HEADLIGHTS mean?
HEADLIGHTS noun- A bright light, with a lens and reflector, on the front of a motor vehicle (or originally a ship or train), designed to illuminate the road when driving at night; normally one of a pair.
- (chiefly in the plural) A woman's breast.
- (chiefly in the plural) A woman's erect nipples, partially masked by clothing.
- (chiefly in the plural) A jewel; especially a diamond.
- (chiefly in the plural) Lysergic acid diethylamide (LSD).