Lightning 101
Lightning 101 and How Lightning Protection Works
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The conditions for lightning begin when humid air rises rapidly and becomes electrified, forming a cumulonimbus thundercloud with separate positive and negative charges. Because of the electrified air in the cloud, an ambient electric field now exists between the cloud and the ground below. Objects on the ground emit positive or negative ions to form a low-density space charge, causing static electricity to build up within the cloud. Lightning is simply a neutralizer – a discharge that can occur from cloud to cloud, within a cloud or from the cloud to the ground. |
It takes only 30 microseconds (a microsecond is one millionth of a second) for lightning to strike. Each lightning strike has an average peak power of 1012 Watts and heats the atmosphere around it to 20,000°C (three times the surface temperature of the sun).
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Although you might think lightning strikes randomly, the “downward leader,” or flash from the cloud, actually interacts with objects on the ground. As the lightning moves toward the ground within the existing electric field, objects on the ground become increasingly electrified and create what are known as “upward streamers.”
If the conditions are right, these upward streamers thermalize and become upward leaders. What the human eye perceives as a lightning strike from above may actually be branches of lightning originating from the ground and the cloud – meeting somewhere in between. These electrified branches complete an ionized path between the cloud and the ground and travel at nearly the speed of light.
Lightning protection systems minimize or prevent intensification of the electrical fields created by objects on the ground and can divert downward leaders to a more attractive strike point.
Where objects are particularly vulnerable, a lightning rod or other type of air terminal can capture a lightning strike and safely conduct the energy to the ground to minimize catastrophic damage. The decision of where to place lightning rods or air terminals is a critical component of a lightning protection system design.
