Lightning is a giant spark of electricity in the atmosphere between clouds, the air, or the ground. In the early stages of development, air acts as an insulator between the positive and negative charges in the cloud and between the cloud and the ground. When the opposite charges builds up enough, this insulating capacity of the air breaks down and there is a rapid discharge of electricity that we know as lightning. The flash of lightning temporarily equalizes the charged regions in the atmosphere until the opposite charges build up again. Lightning can occur between opposite charges within the thunderstorm cloud (intra-cloud lightning) or between opposite charges in the cloud and on the ground (cloud-to-ground lightning).

Historically, the study of lightning can be tracked since Benjamin Franklin (1706 – 1790) era. Franklin concluded that clouds are electrically charged. In the experiment where he standing on an electrical stand, holding an iron rod to gain an electrical discharge between the other hand and a ground, concluded that if the clouds were electrically charged, then sparks would jump between the iron rod and a grounded wire. This experiment was furthered performed by Thomas Francois Dalibard  (1709 –  1799) in  May 1752  where sparks  were observed to jump from the iron rod during a thunderstorm. G.W. Richmann (1711 – 1753) was killed by lightning when he proved that thunderclouds have electrical charge. According to Lukasz Staszewski from University of Technology, Poland, Benjamin Franklin endeavoured to test the theory of sparks shared some similarity with lightning using a spire which was being erected in Philadelphia. While waiting for completion of the spire, he got the idea by using a flying object like a kite. In June 1752, it was reported that he raised a kite. Key was attached on his end of the string, and he tied it to a post with a silk thread. As time passed, loose fibers on the string stretching out, he then brought his hand close to the key  and a  spark  jumped the  gap. The rain had soaked the line and  made  it  conductive. Although this experiment showed that lightning was a discharge of  static electricity, there was little improvement in theoretical understanding for more than 150 years.

Lightning  can be  formed  in  four types of  processes  which  are  charge  separation, leader formation, discharge and re-strike. The process of charge separation is still the subject of research with one hypothesis, the polarization mechanism, which has two components. Firstly,  falling  droplets  of  rain  become  electrically  polarized  as  they  fall  through  the charge separation is trigger by the ionization of an air molecule by an incoming cosmic ray.