Suppose that we repeat the experiment, except that we place the sodium flame in a strong, localized electric field. the field changes the energy levels of the sodium atom, but it does not affect the sodium in the lamp or the photons it produces. the shadow cast by the sodium flame when illuminated by the sodium lamp should stay the same, get darker, or lighter?

Lighter

Explanation:

In practice, the lamp is powered by an AC voltage source which is connected in series with an inductive ballast in order to supply an approximately constant current to the lamp, rather than a constant voltage. This helps to provide a stable operation. The ballast is usually inductive rather than simply being resistive to maximize resistive losses.

As this lamp current tending to zero-current point and shadow cast by the sodium flame becoming lighter.  

wire in brush may conduct electricity from cell to drill and vice versa electrc shock possible

an energy transformation flow diagram is shown

where is it ?