meaning of "A lit light bulb"

[sally hally]

English Language Tests, Intermediate level

ESL/EFL Test #388 "English Slang Idioms (119)", question 5

"Wow, I just had a light ......... moment! I finally understand now how to erase unwanted work in Microsoft Excel!" Brian told Brenda.

(a) house
(b) flash
(c) bulb
(d) bright

English Language Tests, Intermediate level

ESL/EFL Test #388 "English Slang Idioms (119)", answer 5

"Wow, I just had a light bulb moment! I finally understand now how to erase unwanted work in Microsoft Excel!" Brian told Brenda.

Correct answer: (c) bulb

Your answer was: correct
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I don't understand about mean of bulb.

sally hally

[Mister Micawber]

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A lit light bulb (an electric lamp consisting of a glass bulb containing a wire filament) is a traditional graphic symbol for the genesis of an idea. It commonly appears in cartoons and comics.
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Native English teacher at Mister Micawber's