Can not set DirectionalLightShadow's direction

I set its direction below, but it not works. The always lookAt (0,0,0)

  var light = new THREE.DirectionalLight(0xffffff, 1)
  light.lookAt(new THREE.Vector3(400,400,400))
  light.castShadow = true

here is my code on codepen:

[codepen] (

sorry for this question. I solved myself.
I should using to set the light’s direction.As the documentation said:

The DirectionalLight points from its position to target.position. The default position of the target is (0, 0, 0). Note: For the target’s position to be changed to anything other than the default, it must be added to the scene using