The efficient lights are hidden in the top of the door frame. It has one furnace air return register in the hallway. I am trying to decide if it needs an air filter at the return air inlet. A furnace-mounted air filter is the best location for effective air cleaning and for efficient heating and cooling. Check your furnace to see if it has a filter or at least a slot for one.
Most furnaces do.
If you do have a furnace filter, then do not install a return air inlet filter. Two filters in the system may create too much air resistance for the furnace blower to handle. If the air flow is reduced, efficiency will suffer.