In North Carolina, during a 90-minute thunderstorm, they filmed two trees and compared videos of swaying branches on a regular camera with what was seen on the UV camera.
In research published in Geophysical Research Letters, they found that twinkling UV dashes matched up with the tips of branches.
The glows lasted for to three seconds, often hopping from leaf to leaf.
If you had superhuman vision, McFarland said, you’d probably be able to see the hundreds of trees glowing during thunderstorms.
“It’d probably look like a pretty cool light show, as if thousands of UV-flashing fireflies descended on the treetops,” he said.
The scientists hope the discovery will shed light on how thunderstorms electrify the landscape and produce lightning.