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It is the most dangerous form of electricity as it is an uncontrolled phenomenon occurring in nature.

During summer season, in humid conditions, the severe heating of air by sun produces very strong upward moving winds. These winds carry up with them the water contents present in the air and forms clouds. As these winds moves up, the water content changes into droplets and freezes. The freeze droplets fall down. During the downfall, their interaction (a kind of friction) with upward moving warm and humid air causes separation of positive and negative charges within the cloud. It has been found that the positive charges accumulate in the upper part of the cloud while the lower part gathers the negative charges. The positive charges also accumulate on the objects like trees, building, metallic poles, mountains, etc., near the Earth's surface.

As the magnitude of negative charges on the cloud grows they become closer to the positive charges present near the Earth's surface. An attraction between these opposite polarity charges (positive and negative) causes a downward movement of negative charges and an upward movement of positive charges. When these positive and negative charges meet, it causes a spark. Since the movement of charges takes place in zigzag manner it produces streaks of lights. These streaks of light is what we call lightning.

In 1752, Benjamin Franklin showed that lightning is a kind of spark caused by static charges on the clouds by his famous kite experiment.

The high-rise buildings are at the maximum risk from a possible lightning strike. Lightning conductor is a device that is used to save these buildings from damaging effects of lightning. It consists of a conducting metallic rod longer than building height. In recently built buildings, lightning conductor is fixed within the walls of the building. The upper end of the lightning conductor remains in open at the top of the building. It is in Y-shape form. While the lower end of the lightning conductor is buried deep inside the ground and is attached to a copper plate.

When ever lightning strikes the building, it first encounters the upper Y-shaped part of the lightning conductor. The lightning conductor thus transfers all the static electric charges of lightning to the ground through its conducting metallic rod and hence saves the building.