Mask/Shrink a spotlight's field

Hi there,

I'm doing a project in the 3d space and I was wondering how to limit the area affected by a spotlight. There is just one little rectangle I want much lighter than everything else (brightness and contrast effects won't work because this is a 3d project so they will have a very small), however, when I get a spotlight onto it, it also brightens the rest of the scene. Is there any way to mask the spotlight or shrink it entirely?