When we think of lightning, we usually picture jagged bolts striking from a dark cloud to the ground. Those are real, but they’re actually a minority of all lightning. About 75-80% of lightning happens inside a cloud or between two clouds. It’s just less visible from the ground.
Within a thunderstorm cloud, ice crystals and water droplets rub against each other and build up huge static charges - usually with positive charge accumulating at the top and negative charge at the bottom. When the charge difference gets too big, electricity has to discharge to balance things out. Sometimes that discharge zaps inside the same cloud (intracloud lightning). Sometimes it leaps between two nearby clouds (cloud-to-cloud lightning). Less often, the discharge happens between the cloud and the ground (cloud-to-ground lightning).
Cloud-to-ground lightning is the most dangerous to humans and animals, which is why it gets all the attention. But if you could see all the lightning in a thunderstorm, you’d notice most of the flashes are happening within or between clouds - bright internal flickers that light up the storm from inside without ever touching the earth.
