(serfs parma)
IIRC, lighting is created when heavy earth particle or rocks are caught up in the clouds and come back down. So while it is cast with Auram it has a terram part. Remember that the particles that are associated with terram want to come down to earth. Lighting was the rocks coming back to earth.
A&A makes it clear that it is the material cause that determines Form, else earthquakes would be an Auram spell (since air trapped under the earth is the efficient cause of earthquakes). Similiarly, the earth particles returning to earth is the efficient cause of lightning, but the material cause is a weather phenomenon, which is Auram by definition.
A spell to affect electricity would have the material cause of whatever the electricity was in. Thus if in a wire it would be Terram. If sparking through the air, it would be Auram. Possibly. The whole thing is very difficult since concepts of energy (in the sense used here) were not present in Aristotlean physics.
FWIW, Phlogiston was 17th century in origin
Mark
Which is why I suggest it be associated with the desired effect instead. The magus might not even truely be creating electricity in the lightbulb, but since the goal of the electricity is to heat the wire till it glows (a concept any verditius with a forge companion would understand), ignem would seem appropriate.