The most common and most likely answer to this crossword clue is the 9 letter word IRRADIATE
I've seen this crossword clue in The Times
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The straight part
We know that "Cast light on" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cast light on = irradiate.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 IRRADIATE mean?
IRRADIATE verb- To throw rays of light upon; to illuminate; to brighten; to adorn with luster.
- To enlighten intellectually; to illuminate.
- To animate by heat or light.
- To radiate, shed, or diffuse.
- To decorate with shining ornaments.
- To emit rays; to shine.
- To apply radiation to.
- Illuminated; irradiated; made brilliant or splendid.