Did you increase the size of the active region as well? (Lighting is controlled by objects, so it won't happen until they load in)
If you did that and it still doesn't work, there's a few things you could try...
- Have lighting objects always be active, it shouldn't add too much of a performance penalty and it'll prevent them from popping into existence too abruptly. (But it WILL add a bit of performance penalty, so be careful about not having hundreds of lighting objects in the same room)
- Try to avoid clustering too many lighting objects together, since only the 8 nearest ones are used (since there's a hard limit to how many lights the rendering system can handle) and which are the nearest ones can change suddenly.
- It could be worth messing around with lighting sources' radius so they light stuff up less when they're far away (e.g. some code like radius = min(normalradius,<big number> - <number smaller than 1>*point_distance(x,y,player.x,player.y) ), but it could be a bit of work to fine-tune it. (The small number is the factor light radius changes with compared to distance, something like 0.25 should work well, and the big number should be the distance the light radius is fully restored, divided with the small number... if I didn't get the maths wrong, at least x3)