I am not sure you can always make engineering sense out of the "value" that returns when reading a parameter that represents a builtinunit. This is one of those cases. That is why you have to resort to convoluted techniques to get the "AsValueString" in the form of a double you can use for your own calculations. The same sort of thing happens with other MEP unit types.
What reads on the connector is the apparent power and this is what is passed into a space for space schedule totals. If you happen to be asking this question in regard to making space true lighting power totals then you cannot use connector data. A totally different tactic is required.