How do I Set Background image in Flutter?

I am trying to set a background image for the home page. I am getting the image place from start of the screen and filling the width but not the height.
Am I missing something in my code? Are there image standards for flutter? Do images scale based on each phone’s screen resolution?

class BaseLayout extends StatelessWidget{
  @override
  Widget build(BuildContext context){
    return new Scaffold(
      body: new Container(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.start,
          children: [
            new Image.asset("assets/images/bulb.jpg") 
          ]
        )
      )
    );
  }
}