The lightning rod was invented in 1749 by Benjamin Franklin as part of his investigations into the nature of lightning and electricity. He speculated that if a large iron pole with a sharpened tip were placed higher than other conductors in the area, it would attract the energy and harmlessly conduct it to the ground. Franklin's invention is still widely used, protecting many buildings and structures from lightning damage.
Lightning rods use highly conductive metals that carry electrical current better than surrounding objects such as buildings or trees. Although wood and other materials will conduct electricity if the charge is great enough, lightning will take the easiest path to ground, channeling through trees, buildings or people. Materials such as plastic and glass will not conduct electricity until the atmospheric charge is extremely high, so they do not divert current efficiently.
How They Work
When electrical charges build up in the atmosphere, they eventually need a path through which to discharge; many times lightning will strike tall objects with destructive results. A lightning rod intercepts the electrical charge that occurs just before a lightning strike, channelling it safely to the ground. To be most effective, the metal rod should be situated high enough so that electrical charges from the atmosphere will have a better chance of passing through it instead of objects or people. If the electrical charge is allowed to build up substantially, it will eventually discharge through whatever object is nearest.
Up or Down?
Although lightning sometimes appears to strike in a downward direction, the phenomenon occurs as multiple rapid discharges, beginning with invisible ones from from the clouds to the ground followed by return upward strikes to the clouds that are visible. A lightning strike makes several round trips from the clouds to the ground and back again in a fraction of a second.
Path to Ground
By itself, a lightning rod will not prevent or divert lightning strikes; to be effective, it needs a direct and substantial electrical connection to the ground with a conductor. A heavy-gauge metal wire, connected to the lightning rod and the earth carries the electrical charge away from the rod; the ground, being electrically neutral, safely absorbs excess charges, minimizing or eliminating lightning damage.