The most common and most likely answer to this crossword clue is the 9 letter word DELIGHTED
I've seen this crossword clue in The Sunday Telegraph
D
E
L
I
G
H
T
E
D
More clues leading to the result DELIGHTED
- Happy with loss of illumination?
- Over the moon in darkness?
- Luminary in performance is euphoric
- Very happy to be blonde indeed!
- Something done about match, perhaps, that makes one happy
- Pleased with action taken to include illumination
- Pleased to land in river delta
- Happy and frivolous, indeed
- Buoyant inside, act happy
- Mistakenly held, I’d get happy
Buddy explains!

The straight part
We know that "happy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case happy = delighted.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 DELIGHTED mean?
DELIGHTED verb- To give delight to; to affect with great pleasure; to please highly.
- To have or take great pleasure.
- Greatly pleased.
- Filled with wonder and delight.