f.scene.light_manager.light_mode AttributeError when using %run in ipython

I saved the following python script in a file called `light_manager-test.py`:
```python
import mayavi.mlab as mlab
f=mlab.figure()
f.scene.light_manager.light_mode='vtk'
```
When from the ipython prompt I type `%run light_manager-test.py`, I get an AttributeError. `f.scene.light_manager` returns `none`.

However, the same commands work fine if I enter them into ipython line by line:


Why might this be? Should I try different backends? This is using qt.

Start by reproducing the commands in light_manager-test.py through IPython's `%run` with the Qt backend, then compare that with entering them line by line. Investigate why `f.scene.light_manager` is `None` only during `%run`; done means the cause and a concrete fix or supported backend guidance are established.

Written by the indexing model from the issue text.