Low cost light with texture or shader, it's possible ?

The game :
I am creting a Roguelike style game with rooms and a lot of tiles. My goal its to make logics based on light. I would use the unity's default light system (because my sprite renderer uses normal maps and other details).

For static lighting :

The game uses a little lightmap system that substract the color of tiles pixels without light and the color with light to, obtain a light layer.

For dynamic lighting :

Here is the problem. In the first hand i can let my rooms with [500-2000] tile each and put point lights. (reduce performances) In the other hand i can write a texture for each room that include the tiles but now the light system is limited by the Pixel light count in the quality settings. (best i think but i cant up the PixelLightCount to 42 when there are a lot of lights in the room)

The question :

So to reduce the perfomance cost of unity lights, I would create an other kind of light for non important light source. There's no way to create a transprent shader that reveal a part of the map through the shadow or something ? Or another idea ?
Thanks for reply & sorry for bad Ênglyssh

A simple room of the game without any lighting

The same room with the different lights