The idiomatic relationship between out like a light and falling asleep (or being rendered comatose) quickly is easily understood in the context of electric lights extinguished instantly by a switch. The logic would also seem to apply to the blowing out of a candle, the turning down of the wick of an oil lamp, or the closing of a gas jet.
But when and where did the application of the phrase to mean this first take shape?
In searching via ngram, 19th century usage shows up, but most of those references that refer to dimming or extinguishing seem to be focused on fleeting emotions and facial expressions rather than consciousness. Numerous mid 20th century references (at least as early as the 30s) use the phrase in the modern sense.
Does anyone have information as to when and where out like a like started to mean rapid unconsciousness?
Best Answer
Shakespeare, King Lear...
...where The Oxford Shakespeare has the footnote...
In the realm of figurative language, life and consciousness are easily conflated concepts, as are candles and lights (wick, gas, electric, whatever). The basic metaphor has been around a long time.
Under OED's out like a light having lost consciousness, having fainted, or gone to sleep, at once. their first citation is...
...so if you find an earlier usage, I'm sure they'd like to know about it.