The “energy” value from the lighting sensor is a number the lightning sensor itself gives us (we don’t do any calculations with it). We’re still trying to figure out what this number means, though. According to the manufacturer’s spec sheet (Section 8.9.2), “This value is just a pure number and has no physical meaning.”
There is no explanation for how to interpret this value, but it’s probably a safe assumption that the “energy” value indicates the relative strength of the signal detected. Note, however, that a weak/close strike might report the same “energy” as a strong/distant strike.
The sensor also provides an estimated distance to the source of the strike, of course, which is likely the more important and understandable value to most users. Hence, we’ve chosen to ignore the “energy” value in the Smart Weather applications and only report distance and count. We still provide the “energy” value through the API channels in case we (or other developers) figure out a use for it in the future.