the lights are on but nobody's home

Meaning

1. used to describe sb who is stupid, not thinking clearly or not paying attention

From the same entry

• according to lights
• be out like a light
• be in light
• bring to light
• cast light on
• come to light
• in a good, bad, favourable, light
• in the light of
• light at the end of the tunnel
• light dawned
• the light of life
• run a light