How do external circuits in light switching units (such as Lightwave RF) use the mains wiring for power?
A 60W incandescant light bulb requires 500 mA @ 120 V to light it up to full brightness. You can easily pass 10 mA through it &mdash; enough to operate a control module like Lightwave &mdash; without causing it to light up at all.

This is why such modules are often specified to work only with incandescant (resistive) loads. CFLs and LED bulbs will often glow or flicker on the current that they pass.