在英语中，go out 是一个被用来形容火、光、热“熄灭”的短语。成语 go out like a light 其实就是通过光亮熄灭的速度很快这一特征，来比喻某人“立马就入睡、瞬间就失去意识”，它的第一种含义类似于汉语里所说的“一沾枕头就能睡着”。

例句

I have no problem sleeping, I go out like a light as soon as I hit the pillow.

我睡眠一向很好，只要一沾枕头，马上就能睡着。

My daughter seems to love this lullaby. She goes out like a light when I hum it to her.

看来我女儿很喜欢这首摇篮曲。每当我哼唱这段旋律时她就会立刻睡着。

I'm not sure if I should lay down in bed right after dinner – I'd probably go out like a light.

我不知道是不是该吃完晚饭后就立刻躺下，我很可能一沾枕头就睡着了。