"out like a light" 的定义和意义

What is the origin of the idiom "out like a light" and when to use it?

The idiom "out like a light" originates from the imagery of a sudden and deep state of unconsciousness or sleep, where an individual falls asleep or loses consciousness very quickly, just as if a light were turned off. It is often used to describe someone who becomes completely relaxed or falls asleep so rapidly that there is no resistance or struggle. The expression has been used since the early 20th century to describe the swiftness and completeness with which someone enters a deep sleep or unconscious state.