Screen go darker when it look at an Object?

The easiest way to darken the screen is to place a black texture in front of the camera and control its alpha value - 0 is normal screen, 1 is completely dark.
If you want the darkness to be max when looking directly to the object, and gradually reduce as you look to other direction, use a dot product to calculate the alpha (camera script):

var black: Texture2D; // drag a black texture of any size here var target: Transform; // drag the object here var sensitivity: float = 1; // darkness sensibility to the angle

private var darkness: float = 0;

function Update(){ // find the object direction normalized: var dir = (target.position - transform.position).normalized; // darkness is max when looking directly to the object: darkness = 1 + sensitivity * (Vector3.Dot(dir, transform.forward)-1); }

function OnGUI(){ GUI.color.a = Mathf.Clamp(darkness, 0, 1); // set the black alpha GUI.DrawTexture(Rect(0, 0, Screen.width, Screen.height), black); }