What is the origin of the idiom "the lights are on, but nobody is home" and when to use it?

The exact origin of the idiom "the lights are on, but nobody is home" is unclear. It has been in use for quite some time, and its origins are likely rooted in the concept of a house or building with illuminated lights but no signs of activity or inhabitants. The phrase is a figurative expression, drawing a comparison between physical presence and mental absence. It has become a common idiomatic expression in the English language to express the notion of someone being mentally absent or disconnected despite physically being present. It conveys a sense of someone being inattentive or unresponsive, as if their mind is elsewhere or not actively engaged.