I doubt if it’s viable or not, because if someone want to raid, he’ll see if towers are on or not and take advantage of it.
Yes, it should exist a way to know, at least for the one who build the tower, if it’s activated or not, but that’s not the best way (which is not bad at all) to make it.
+1
Sorry for my English, I think the idea is very good and it would be possible if the system of lights appears only for its tribe and its owners, so it is individual by tribe or base.