How do you "stop" light at plain edges? is it possible?

Hello!

So, i have been messing around with babylonjs for a couple weeks now, just trying different stuff out, now, i have a rectangular plain, aprox 150x100,

i want the "center" of the plain to be well lit from all directions, while at the edge, the light should rapidly fade out to black,

I have tried several set-ups, 

so far, the best results i've gotten regarding getting the fade-out effect is using 3 spotlights(1 in each end and 1 in the middel of the plain), but since they only cast light from above, all the objects sides are completely black.

Does anyone have a solution for this? is it even possible?

var light0 = new BABYLON.SpotLight("Spot0", new BABYLON.Vector3(0, 100, 0), new BABYLON.Vector3(0, -1, 0), 0.8, 2, scene);
	light0.diffuse = new BABYLON.Color3(1, 1, 1);
	light0.specular = new BABYLON.Color3(0, 0, 0);