「おれのへやわよじょうはんです」 - Rooms in japan are often described in tatami size. 4.5 tatami is the size i prefer, everything else feels too big.

行灯 (andon) is the name of that traditional Japanese lamp made of stretched paper over a frame of bamboo (other types of wood and even metal are used as well, but it's not as common) in a rectangular shape.

So 「昼行灯」(hiru andon, "daytime lamp") is an expression used to describe something or someone that seems to have no purpose.