Lightning is a sudden, very large electrical discharge in the atmosphere that creates a bright flash of light and is usually produced by thunderstorms. It happens when electric charges build up and overcome the insulating ability of air, allowing electricity to travel rapidly between a cloud and the ground, within a cloud, or between clouds.

How lightning forms

Inside a storm cloud, collisions between ice, water droplets, and snow separate electric charges so that negative charge tends to gather near the cloud base and positive charge near the top or on the ground below. When the difference in charge becomes strong enough, a conductive channel forms through the air and a powerful current flows, which is seen as lightning.

Lightning and thunder

A lightning channel heats the surrounding air to tens of thousands of degrees Celsius in a fraction of a second, much hotter than the surface of the Sun. This extreme, rapid heating makes the air expand explosively, producing the shock wave that is heard as thunder.

Key properties

A typical lightning flash can involve hundreds of megajoules of energy and voltages in the hundreds of millions to around a billion volts. Most lightning stays within clouds, but cloud‑to‑ground strikes also occur frequently and can be deadly and destructive.

Simple comparison table

Aspect| Description
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What it is| A giant atmospheric electrical discharge that briefly neutralizes charge imbalances.15
Where it occurs| Within a cloud, between clouds, between cloud and air, or between cloud and ground.36
What it causes| Bright flash of light and rapid air expansion that produces thunder and can cause damage or injury.27