Why Does Lightning Flash? Causes and Safety Tips

A sudden blinding flash among dark monsoon clouds, then a huge rumble — it is nature's most powerful show. Why does lightning flash? The question has puzzled people for thousands of years. Science now knows the answer — and how we can stay safe. Thousands of people die from lightning strikes in India every year, so knowing the safety rules matters a great deal.

How does lightning form in clouds?

Thunderclouds (cumulonimbus clouds) are several kilometres tall. Inside them, strong winds toss particles — water drops, ice crystals and hailstones — up and down. As they collide, the particles pick up electric charge: lighter particles carry positive charge to the top, and heavier ones keep negative charge lower down. When this difference becomes very large, the air can no longer hold it back, and the charge rushes across in a giant spark in a split second — that is lightning. It can flash inside a cloud, between two clouds, or from a cloud to the ground.

Why does thunder follow?

A lightning flash heats the air to about 30,000 degrees Celsius in an instant — several times hotter than the surface of the Sun. The air expands suddenly and violently, making a sound like an explosion — that is thunder. Light travels much faster than sound, so we see the flash first and hear the thunder later. Count the seconds between the flash and the thunder and divide by 3 to get the rough distance of the lightning in kilometres — a trick also found in 12 interesting physics facts.

Did you know? "Lightning never strikes the same place twice" is a myth. Tall buildings are struck again and again; the Empire State Building in New York is hit more than 20 times a year on average.

Lightning in India: a big danger

According to National Crime Records Bureau (NCRB) figures, lightning causes the largest share of deaths from natural disasters in India — about 2,500 to 3,000 people lose their lives to it every year. Most of the victims are farmers and labourers working in the fields. States such as Odisha, Jharkhand, Bihar, Madhya Pradesh and West Bengal are among the worst affected.

How to stay safe

Do	Don't
Go into a solid building or a closed vehicle as soon as you hear thunder	Don't shelter under a tree
If caught in the open, crouch low with your feet together and head down	Don't lie flat on the ground
Keep away from water, ponds and rivers	Don't stand near electric poles or metal fences
Go out only 30 minutes after the last thunder	Avoid corded phones and bathing during the storm

A closed car is considered safe from lightning, because its metal body carries the current around the outside to the ground. The "Damini" app of the Government of India's Indian Institute of Tropical Meteorology (IITM), Pune, gives advance warnings of lightning strikes in your area. A lightning conductor on houses and tall buildings carries lightning safely into the ground — it was invented in the 1750s by the American scientist Benjamin Franklin.

Key points

Colliding particles in tall clouds build up charges; when they discharge, lightning flashes.
Lightning heats the air to about 30,000 degrees Celsius; the expanding air makes thunder.
Thousands of people die from lightning strikes in India every year.
Don't stand under a tree; a solid building or a closed car is the safest place.
The "Damini" app gives advance warnings of lightning.

Frequently asked questions

Why do we see lightning before we hear thunder?

Because light travels about 3 lakh (300,000) kilometres a second, while sound travels only about 343 metres a second.

Do mobile phones attract lightning?

No, a mobile phone does not attract lightning. The real danger is being in an open field, on high ground or near water.

Why does lightning flash? The causes, and how to stay safe