It's much better to extend the wifi network.
Not only is it safer than some diy lamp fitting -> mains plug but it will also benefit you in the wifi reception in the house.
It's very cheap and very simple.
Go to any place where you can buy used stuff, someone will sell a router cheap because "the switched provider".
What they don't know is that most routers work fine whatever provider you have.
I have "three" different providers in my house. The cheapest was bought for about £ 0.1.
The only thing that can be problematic is to wire the network cable between the two routers nicely in the house.
They should be connected lan to lan.
Put power on the "new" router and connect it with a cable to a computer.
Open the settings IP in the browser and turn off DHCP and give the router a static IP. Usually it's between 192.168.1.1 to 192.168.1.255 .
I usually give it something in the 200 range to not interfere with the your current devices (unless you have 200+ devices already).
Set up the wifi name and password the exact same as on your old router save and restart.
Unplug the computer.
So the first router should have a cable going to the internet port as I assume you have, then put a network cable (a long one to extend the network) in any of the other four ports, on router 2 you connect it to Port 1-4 (not internet).
That is it.
It really is the cable management that is the hardest part.
Is this "lighting ring" 120V or 12V? Is it constantly powered or switched? I believe that the Homeplug adapters draw their own power from the power line, and hence they would not work on 12V, nor when a 120V line is switched off. LEDs can produce substantial interference, though generally not as bad as fluorescents. – Daniel R Hicks – 2013-09-09T11:19:18.730
@Daniel - it's 240v (UK) and the ring part of it is not switched. I think I'll just have to give it a go and see how much interference the LEDs & fluorescents bulbs put out. – Mark – 2013-09-09T14:35:51.670