How to fade a room to black with static lighting?

Hi everyone. I’m sure it’s just wishful thinking, but I was wondering if anyone has some clever way of fading to black baked-in lighting on a portion of the screen. Essentially, I need the lights to fade when the character goes to a different room (the first room will be visible on screen but dark. To get the desired effect, I’ll need to do this many times through out the game as the character walks from place to place, so it can’t be super expensive resource-wise.

A big part of the game mechanics rely on manipulating lighting in different ways and so there are quite a few movable lights roaming the screen at any given time and the lighting cost is pretty high as is. I can’t do an entirely dynamic setup.

So far, I’ve tried:

  1. Using a post process blend to animate exposure - This fades, but applies to the entire screen.

  2. Placing a black tile over the section and animating its opacity. - The fade looks unnatural and gets tedious and expensive, especially with non-square rooms.

  3. Praying - So far, nothing. I’ll keep everyone posted.

Again, thanks to anyone with ideas.
Cheers.

For the sake of completion, I ended up solving this by using unlit black tiles as rooftops and fading them in and out by animating their material opacity using trigger boxes and the timeline node. The trick was to make the tiles unlit.