i have moonlights on my tank. came in handy when i had my bumblebee cat. never saw it untill i installed the moonlights. you can buy them ready made from most shops and of course ebay.
i made mine from cold cathode tubes, the ones for lighting up PC towers. i got mine in a kit (2 CCT's and a power invertor) from from maplin for £8. but you could get them from most PC shops. i just connected mine up to a variable voltage power adapter i had, and hey presto! a monlight system for £8.
i have seen power adapters for less then £1, but normally around £3 so the total cost to collect everything from scratch is £11. this is fine on my 3ft tank but for bigger tanks it may be worth buying more kits, as you can only run two tubes per invertor. or you could just turn the voltage up to compensate. i run mine at 4.5v and its just light enough to see my fish, but not too bright to spook them... you can go to 12v though if you need to.