Light bandings

Hello,

First of all i want to say that i'm unity beginner.

I'm trying to make 2D game with graphics oriented on contrast. But here i found a problem when i create a light with unity there is a lot of gradient banding. Banding is normally problem of textures/sprites/images but i didn't expect it with unity created light.

If you'll look carefully, you'll see banding.

Any tips please ?

Thanks for help !!