(The answer survived a triple check of the logic, mostly by pure luck. The readability of my explanation didn't survive; so here's is a rewrite.)
The house has two repeating runs of 27 consecutive rooms: the first one starts at room 20 and repeats at room 50, and the other one starts at room 128 and repeats at room 170. However, it's still possible to determine the starting room with only
26 room visits.
We need to start in the ascending direction. If we started in a dark room, and the next rooms are either "dark, light" or "dark, dark, light", we'll turn back. Otherwise we'll just keep going until we've collected a sequence that uniquely defines our starting room.
This method works, because it makes sure we won't hit the worst case scenarios (or even the second worst case scenarios), because all the mutually indistinguishable 27-room repeat sequences happen to begin with "dark-dark-dark-lit", and the method detects and avoids them before it's too late.
On the other hand, even though it "wastes" a visit (or three), we are ok with turning back at the first lit room, if it occurs that early:
All backwards sequences of length 23 that start with "lit-dark-dark-dark" are unique. Here's the program (Try it online!) that I used to verify it.
So if we hit the special case, we visit at most 4 rooms (incl. starting and turning room) going forward, and then at most 22 more going backward.
OTOH, if we don't hit the special case, we know we didn't start at the worst possible spot (20, 50, 128 or 170), and neither did we start at the second worst possible spot (21, 51, 129 or 171), so we are guaranteed to find the solution in 26 visits in that case too.
Note that I didn't use a program to prove optimality (or to find a better answer): this puzzle comes with the no-computers tag, so anything more than proofreading by computer would have felt like cheating.
About the possibility of future improvement: the 27-room runs all end in lit-dark-lit-dark-dark-dark, and any forward sequence starting "lit-dark-lit" becomes uniquely defined in 19 rooms or less. However, there's a 25-room duplicate run (at 42-66 and 162-186) that comes into play if we try to go lower than 26 rooms. Since that run cannot be usefully detected until it's just barely too late to turn away (it seems so, because it ends in lit-dark-lit-5darks, and that just happens to be one of those lit-dark-lits that require all the 19 rooms to solve), it seems that all these attempts must top out at 26 rooms at the minimum, too. Unless I've missed something, of course.