I was wondering how is the energy of a lightning measured? Is it based on the luminous intensity and/or the generated sound? What about the generated heat and energy spent in the production of ozone? Is it taken into account?
It is difficult to measure, but a bulk of it's energy is not spent in ionizing the atmosphere or in the sound wave but in the movement of charge itself. However lightening labs will measure a variety of factors to characterize the strike.
They launch small rockets carrying a small wire or sometimes emit some conductive ionized gas which triggers a strike right where they want it. They then study the dynamic charge both on the down strike and the ground return. Clustered around the strike zone are a range of instruments and detectors that measure the size of the current, the power of the sound waves, and the brilliance of the flash.
The head of ICLRT describes the computational process:
"Initially, there will be two waves or pulses propagating in opposite directions from the tower top. Each of those two waves will contribute to the magnetic field measured by the lightning detection network."
They use this data to characterize the energy as each strike can be different. Each year this lab triggers 30 to 50 strikes to test equipment and develop proper test procedures for making products (like airplanes) safe from strikes.