The last step of this process is not obvious. Intuitively, the clamping voltage should simply be provided on the datasheet along with the power rating. This is true, but the transients used to derive these ratings must be considered. These transients are very different than the transients to which the components will be exposed during the application of the lightning test transients. References[8-13] are examples of datasheets for the components used in lightning protection circuits.