light bulb gone off

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Senior Member
Hello, guys!
This is from 'Dear Entrepreneur'

So has the light bulb gone off or has it been an idea slowly cooking in your brain for months or even years? For me it was a light bulb moment pure and simple.
I wonder 'gone off' in 'light bulb gone off' means 'turned off' or 'turned on'.

The 'off' in 'light bulb gone off' suggests it means 'turned off' but it seems to mean 'turned on' by the context. So I'm a bit confused.

Could you please help me?
  • e2efour

    Senior Member
    UK English
    This appears to be an American idiom, meaning I had a flash of inspiration or The penny dropped.
    I have never heard it before, although gone off seems not to mean went out or went (failed).
    Last edited:

    Language Hound

    Senior Member
    American English
    Yes, we do say "a light bulb went off" to mean we had a sudden flash of inspiration or understanding.
    It's just a set phrase, which I don't think many native AE speakers even think about until asked why we say "off."

    From Collins:
    light bulb moment
    1. a moment of sudden inspiration, revelation, or recognition
    [C20: from the cartoon image of a light bulb lighting up above a character's head when he or she has an idea]

    Some of the explanations for using "off" I've found online include the following:
    The light they say is going "off" is like the old flash bulb [on a camera] "going off", more of a bright explosion kind of thing to mark your eureka moment." Source

    I believe that the phrase "a light bulb went off" evolved from "a bomb went off" (meaning that a bomb exploded). The 'correct' phrase should be "a light bulb came on" because a lit light bulb above a person's head symbolizes enlightenment. In animated cartoons such a light bulb goes from being off to suddenly being on. That suddenness could be characterized by an exploding bomb. Thus, combining those two ideas, results in "a light bulb went off." Source
    These are just theories. Perhaps someone will be able to locate an authoritative source that gives a definitive answer.


    Senior Member
    English (U.S.)
    I have never heard, and would never say, the the "light bulb" representing sudden inspiration has "gone off", and I don't recognize it as a set phrase. A light that "goes off" ceases to give light, so it would not make sense here; I would instead say that it "came on", or "turned on", or "lit up" -- any of which I would call a version of a standard phrase. If "goes off" is a common error, as Language Hound's explanation suggests, then it is not one with which this speaker of American English is remotely familiar.

    Language Hound

    Senior Member
    American English
    I have always heard, read and said "A light bulb went off (in his/her/my mind/head)."
    However, the Merriam-Webster Learner's Dictionary allows for both "off" and "on." :idea:

    a light bulb goes off/on
    chiefly US, informal

    ◊ When a light bulb goes off/on (in your head), you suddenly understand something or have 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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