Take the cover off of the ballast, and read the information sticker on it. It should tell you what lights it is designed for. (example "f40t12") Then once you know what lights they are, call your local hardware stores and inquire about those bulbs. Make sure they have the same kelvin rating, unless you want lower ones. You can save tons by buying at the hardware store. I found
HO T5s at the home depot here in London for 9 a bulb. If you are interested in saving some money, I would read up on
DIY light hoods in the DYI section of the forum. Lighting is super easy to build, and does not cost much at all. I say tear that thing apart and build a light suited for your needs inside its shell, then you will know how much replacements cost and you will have no worry about one light going out and the others not working. Is this for your 92 gallon?
I am not sure about the lights being on a loop system, I have no experience with this product, but Im sure someone will be along shortly to tell you their experience with this product.
Good luck with your lighting bobby!! Cheers!!