After the correct comments, you are asking about the number of photons. Now it is only possible to calculate if you use an average wavelength (frequency). I chose visible light wavelength. This calculation can be done with a different wavelength too.

Assume visible photons, there is 2 eV in a photon.

A lightning has 1 billion Joules (6.24*e^27 eV).

This makes 3.12*e^27 photons.