Lighting for 2d game

Hi , i am currently on the making of a 2d game for now some time and i have i problem that i dont manage to fix alone :

Currently any light that i put on facing my tilemap to light it up will just light the bottom part of the light and then the top part of the light will be lighting the back of the tilemap … i really dont know how this can happen , i am using basic lit material to allow lighting

Thanks in advance for any help !

I met the problem, too.