a light bulb goes off/on (in someone's head)
idiom
chiefly US, informal
—used to say that a person suddenly understands something or has a great idea
After thinking about the problem for several days, a light bulb went off in her head, and she knew how to solve it.
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“A light bulb goes off/on (in someone's head).” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/a%20light%20bulb%20goes%20off%2Fon%20%28in%20someone%27s%20head%29. Accessed 31 Jul. 2025.
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Merriam-Webster unabridged
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