Rare image shows lightning rods in action in São Paulo – 03/31/2023 – Science

Benjamin Franklin invented lightning rods in the 18th century, and the devices have protected buildings and people from the destructive forces of lightning ever since. But the details of how they work are still the subject of scientific research.

Although modern lightning protection systems involve extra equipment that makes them more efficient, the lightning rod itself is quite simple: a copper or aluminum rod placed above the highest point of a building, with wires connected to the ground. When lightning strikes a building, it preferentially travels down the rod—the path of least resistance—and then down the wires to the ground, protecting the building and its contents from the extremely high currents and voltages produced by lightning.

But a rod does not wait for lightning to strike. Less than 1 millisecond before the discharge touches it, the rod, triggered by the presence of the negative lightning discharge, sends a positive discharge upward to connect with it.

Recently, Brazilian researchers were lucky enough to photograph this event with high-speed, high-resolution video cameras. They captured the electrical action in São José dos Campos, in the northeast region of the state of São Paulo.

Scientists were in the right place at the right time with the right equipment to capture 31 of these upward discharges as they happened. With its location, about 150 meters from the rays, and its camera that registers 40,000 images per second, they were able to take clear photos and make a slow motion video of what happens in the instant before the charge of the rod meets the charge of the ray. The scientists’ study and photos were published in Geophysical Research Letters in December.

---

Video shows how lightning rods work

---

It wasn’t just lightning rods that produced these discharges, but also various corners of buildings and other high points. In fact, “anyone who is in an open area can throw a connection discharge upwards, from their head or shoulders, and be injured by lightning, even if they are not directly hit by it”, said Marcelo Saba, senior researcher at the Inpe (National Institute for Space Research) and author of the study.

Does one type of lightning rod offer better protection than another?

“Some vendors say their arresters are better than others,” Saba said, “but that’s just talk. There’s no solid research on this. There are rules that anyone who installs lightning arresters must follow. It’s the best. what can we do for now.”

^{Translated by Luiz Roberto M. Gonçalves}