Don't know what's inside an 18watt light.
Any system will have risks associated with it.The dumb light will cater for a failure of the home automation (HA) system.However, I could still make it controllable...
Those ceiling lights have five 0.2watt LEDs in parallel.Power rating of the light is how many of those groups of five are connected in series.6 groups for a 6watt light, and 12 groups for a 12watt light.A 12watt light (60 LEDs) would need a 36-40volt supply.
I think except from EMI you have to worry about all those things I think.Aka, not a very good design to do so
For a high impedance signal: keep it on the PCB.For a low impedance signal (aka it has real load) < 1m I would say.