Hi
I don't know if you are in the UK but I have some 240 V direct replacement for the 55W plug in spots, they were only about £2 or £3 each and they pull 3 W from the mains. I have one over a stair well which is always dark and it is on 24Hrs.
You can use capacitors as a way of reducing the mains to an alternative voltage, but I personally don't think it is worth the effort when off the shelf units are readily available.
You can also buy 12V replacement lamps. Look on EBay I am sure you will find something.
Brian