In this post, NASA's Earth Observatory drops some facts on the cause, detection, and number of lightning bolts in our active atmosphere:

Across the atmosphere of Earth, lightning flashes about 50 times per second. That’s 4.3 million times a day and roughly 1.5 billion times a year. Using a new instrument on the International Space Station (ISS), scientists are hoping to observe and dissect at least a few of those lightning bolts every day.

The thunderstorm in the beautiful image below was captured over the country of Bolivia: