Our story starts in 1761 with Ebenezer Kinnersley. In a letter to Benjamin Franklin he described experiments he did for testing if heat was produced by electricity. His power sources were electrostatically charged capacitors made with a case of bottles, or Leyden jars, batteries not having been invented yet. To get sufficient current to detect a change in temperature he needed to release all the stored charge at once through a spark gap. In one experiment (Expt. 11 in the letter) the current was sufficient to make a brass wire turn red.
Today we say that the wire became incandescent, it emitted electromagnetic radiation in the form of visible light as a result of the heat. He also arranged the experiment such that the wire was suspended with a weight at its bottom and found that it elongated by an inch when it got red-hot, the first indication that such heating can be destructive to the wire. He experimented with different diameter wires all of the same material and found that the larger ones showed no noticeable heating effect and concluded that this was due to the lower resistance of the larger ones.
TLDR; Edison did not invent the incandescent lightbulb.
