I have hooked up a string of LED Christmas lights to an x10 appliance module as a test. They turn on fine but when they turn on they are still on, but very dim. Any reason why this should happen? I thought Appliance modules mechanically cut the source power.
Nope - appliance AND lamp modules trickle current through the string for "local sensing" (which allows the modules to turn on by jiggling a lamp's built-in switch) and that makes the phantom glow. It's also the culprit behind the flashing (and relighting) of CFL bulbs that are run on appliance modules.
There are various circuit mods (usually involving cutting a trace or a component lead in the module) you can try that are pretty simple but of varying effectiveness, or you can add a small tungsten string or nightlight bulb to the load. This very often stops the phantom glow.
IIRC, Smarthome made a module that allowed you to programmatically disable "current sense switching" that would also eliminate the problem. I've also had some luck piggybacking modules so that it would take two commands to light the string. Plug a module set to A2 into a module set to A1 and then it would take A1 ON, A2 ON to light the string. IIRC, it's not a guarantee.
I just got a new string of LED lights, so I'll give it a try and let you know.
We have some of our home lights wired up with two on/off switches, so the lights are off when either both switches are off or both on.
If we leave the switches both on, the lights should be off, but they is sufficient induced voltage in the wiring to leave the LED lights very very slightly on! These are LED GU10 lights normally running at
LEDS are so efficient, they need very very little current to produce a little light.