You could place “understanding” at many points in history, and several in the future:

Building an arclamp powered by a portable generator is damned impressive.

Sending a message via electromagnetic waves shows very impressive understanding of electricity too.

Having a small electromagnetic particle accelerator in your house to show moving pictures is pretty damned amazing.

Using electricity and basically sand to do maths is insanely impressive.

On the other hand, you might argue we don’t understand electricity because we don’t have a unified field theory.