The most common and most likely answer to this crossword clue is the 7 letter word FLASHER
I've seen this crossword clue in The Guardian
F
L
A
S
H
E
R
More clues leading to the result FLASHER
Buddy explains!
The straight part
We know that "Bulb/one unexpectedly discovers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bulb/one unexpectedly discovers = flasher.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 FLASHER mean?
FLASHER noun- Anything that flashes, especially a device that switches a light on and off.
- An indicator or turn signal.
- A person who exposes their genitals or female nipples.