@MrCrayfish

In the v4.0pre1 version the Lamp is no longer in the inventory to select. If you were to pick up a previously place lamp (placed before the update) it would be named tile.lamp_off.name or tile.lamp_on.name. Also tile.lamp_on.name has a missing icon texture. It is still possible to craft the Lamp.

Pictures:

^Lamp can not be found in the Furniture Mod inventory menu.