Table lamps ... incandescant should be fine, but LED or CFLs may present a problem as they can generate a lot of RF noise.
You also need to consider how many RCDs or RCBOs the signal might pass through. The very nature of them means that they can and do filter out high frequency signals.
Personally, I would go for external Cat5e = possibly SWA too. If you are going across/down a lawn, feed it through hose pipe for extra protection then with a lawn edging tool or flat spade cut a 6" deep slot. Get the pipe in the bottom and fill with soil.
M H C
taurus excreta cerebrum vincit