While air is generally considered a poor conductor of electricity, its behavior during lightning can be attributed to a phenomenon known as electrical breakdown. When the electric field strength in the air exceeds a certain critical value, the air molecules become ionized, creating a path of reduced resistance for electrical current to flow. This critical field strength is called the dielectric strength or breakdown strength of the air.

During a lightning discharge, the buildup of electrical charges in the atmosphere creates an intense electric field between the charged regions. As the field strength approaches the dielectric strength of air, the air molecules undergo a process called ionization. This means that electrons are stripped off from their parent atoms or molecules, leaving them positively charged. These free electrons and ions then become available to carry electrical current.

As the electric field continues to strengthen, more and more air molecules become ionized, forming a conductive channel of plasma. This plasma channel provides a low-resistance path for the electrical current to travel, allowing the massive electrical discharge of a lightning strike. The high temperatures and pressures generated during the lightning discharge further aid in the ionization process, leading to the creation of even more plasma and the propagation of the lightning leader towards the ground.

Once the lightning leader connects to a grounded object, such as a tree, building, or the Earth's surface, the main electrical discharge follows the established channel, releasing an enormous amount of energy in the form of heat, light, and sound. This process demonstrates how air, despite its low electrical conductivity under normal conditions, can become a temporary conductor during lightning due to electrical breakdown and plasma formation.