The most common and most likely answer to this crossword clue is the 12 letter word LUMINESCENCE
L
U
M
I
N
E
S
C
E
N
C
E
Buddy explains!

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 LUMINESCENCE mean?
LUMINESCENCE noun- Any emission of light that cannot be attributed merely to the temperature of the emitting body.