Thanks Pete for the info. That helps a lot. Why did you use relays instead of buying X-10 equipped floodlights?
Obed
In new construction where installation's not a problem, the relay is very cheap and reliable. The only challenge is finding various closets where you can hide the boxes for the relays. Only down side is you have to have the automation stuff going to use them in an automated way. The switches will always work whether you have automation or not.
It seems like I could use relays too, even though the sheetrock is up. I believe I can get to the flood light wiring in the trusses via the attic. Couldn't I just add a junction box and put the relay in parallel with the light switch? That way either the automation controller or the light switch could turn on the light.
Obed
If the light is a single switch control, you can certainly parallel the relay contacts with the switch. For a three way or more, then you need access to the wire that goes to the light and the power for that circuit. Note also that sometimes things are wired with power at the light, and the run to the switch is just the switch leg. Sometimes things are wired with power at the switches and the run to the light is just the light so you'd have to find the power circuit somewhere else. You _really_ want that to be the same circuit as the light so if you or someone else goes to work on the light, when they pop the circuit breaker off you are guaranteed everything is off. So figure out how your place is wired so you know what you have to do. In my house, power is always at the switches and not the light(s).
What I did was bring a 14-3 from the switch box that has the wire that goes to the light. The black wire was the power for that circuit. The red wire went to the light. The white wire (with a piece of red tape around it so no one confuses it with neutral) was the "output" from the switch(es) that would have gone to the light in normal circumstances. This means that the switch(es) can run the light on their own with no automation, but the automation system can turn on the light whenever it wants independent of the switch(es). Failure of the automation system means that everything still works manually.
The 14-3 is run to a box where you can have access, and a low voltage wire (I used an 18-2) goes into the box too. The light (red) goes to the common of the relay. The black goes to the normally open, the white to the normally closed. I had a little PCB that takes up 2 spaces (I'm re-doing it to fit in a single space), so just use a box one size bigger so you can wire it up.
Obed, for a relay retrofit, just be sure that when you put your relay in up in the truss area that the power for it is the same circuit as the switch. This gets back to how your place is wired. I know of someone who used the other phase and sometimes when the light was already on and the relay was used, it arced and shorted out the 240 phase popping the breaker. He broke all the rules. Be sure the relay is in a nice box since it will be hot up there in the attic. If the coil goes, you'll want to be able to contain it.
I've heard that X-10 can be a little flaky. Maybe I'll check to see if UPB is available for the HAI OmniPro II. Requiring a serial port surprises me, seems a little behind the times.
Obed
Well, no one can agree on anything about home automation. The physical layer (serial, USB, X10, UPB, Zigbee, other 2.3GHz stuff) and the packet format. The collective efforts of all the companies got nothing on the Tower of Babble. Ethernet would be nice, but the cost is very high. X10 just has a volume, overseas production, and 1st to market going for it but that's about it. So lots of automation controllers have a few extra serial ports for this sort of thing. You find serial ports on weather stations, solar panel inverters, floor heating systems, and other devices just because they are cheap and well known. Lots of single chip controllers have serial ports on them, so the cost is just the RS-232 level conversion. Now you're down to just a wire and connector difference. Topic for another day, but, all my efforts are to interface to this hodge podge of stuff and come out with an Ethernet jack, published open protocols, and open source code for the lower level layers. Ethernet is now available on single chip computers, and if home automation every really becomes mainline it will become more popular.
So if you can relay, great. If not, see if the HAI supports UPB. If not, see if your light positions will work with X10 stuff. Note that if you're confident you can retrofit a relay, you can just put a normal fixture for now (least time and effort), get your CO, and then retrofit when the fog has cleared. And if you go the relay route, I can help you on the relay stuff.
Pete