Power measurement in a two-wire load control device

A two-wire lighting control device for controlling an amount of power delivered from an alternating current (AC) power source to a lighting load, the two-wire lighting control device comprising:

• a controllably conductive device configured to be coupled in series electrical connection between the AC power source and the lighting load;
• a control circuit configured to render the controllably conductive device non-conductive during a first portion of a half-cycle of an AC waveform and render the controllably conductive device conductive during a second portion of the half-cycle to control the amount of power delivered to the lighting load;
• a voltage measuring circuit configured to measure a voltage across the two-wire lighting control device during the first portion of the half-cycle;
• a signal generator configured to generate a complementary voltage waveform that approximates a voltage across the lighting load during the second portion of the half-cycle, wherein the complementary voltage waveform is based on the voltage measured across the two-wire lighting control device during the first portion of the half-cycle;
• and
• a current measuring circuit configured to measure a current supplied to the lighting load from the two-wire load control device during the second portion of the half-cycle;
• wherein the control circuit is further configured to compute an estimated amount of power consumed by the lighting load based on the complementary voltage waveform and the current supplied to the lighting load during the second portion of the half-cycle.