Ah, I see. Then the problem is that the outdoors is a huge room.
In the future Rhys might change/improve how lighting works so that each light lights up it's own area but for now the game does light the way the original game did and it stays dark/dim until you have enough lights and then lights up the room. So, unfortunately, you need to section the area off with walls to create a smaller room. This will also give you some control over the room-score. Obviously walling up a space that is meant to be outdoors is a bit disappointing, but it's the only option right now.
Fence-walls appear to only be semi-walls so, sadly, wont really help in this case. But pool-moats may (I haven't had a chance to test that personally in the live game), if you don't mind having people climb in and then out of pools to reach the area.