vtkLightActor rendered size

I am trying to use vtkLightActor but the data I am visualising is rather large, so 10 m so 10000 mm. All my datas units are mm, so when I put add vtkLightActor to my renderer, it appears very small. I would expect I need to scale the actor using vtkLightActor.SetScale, but this does not appear to work. I have tested my application scaling everything down and I can view the vtkLightActors.

Any help much appreciated