When we moved into our new house, the developers had decided to light almost the entire house with halogen spot lights. Initially I didn’t pay too much attention to this, until after the first winter I was looking at the electricity bill.
Since I didn’t think we using more than our previous house, I did some quick back of an envelope calculation and results were quite eye-opening.
The house had 48 50W spot-lights and 3 20W down-lights. (When I came to replace them, I discovered that most lights were MR11s, each running off its own transformer also.) There were a few GU10 bulbs also.
My gut-feeling was that this was probably quite expensive to run, however I didn’t have the figures, so I did some rough calculations.