Why is there a mirror on the ceiling of the couple's room?

In order to visually increase the effect of space.

A double mirror is a kind of optical glass. From one side, it is an ordinary mirror, and you can't see the scenery behind it. From the other side, it is transparent glass, and you can clearly see the opposite scenery. To identify whether it is a double mirror, you can point your finger at the mirror. When there is no gap between your finger and the finger in the mirror, it is a double mirror, and vice versa.