Last month's electricity consumption was our lowest ever, at 192 kWh. However, it's not possible to put this down to any one cause, as SWMBO has taken to such things as making curry, etc, by the gallon and freezing the portions, saving on cooking time.
However, the usage of the hall and landing lights remains fairly constant; in winter (which lasted 4 months here this year) they are on 16 hours a day, and for the other 4 months they have been fitted, 5 hours a day.
4 months x 30 days x 16 hours x (4 x 20 - 4 x 4) = 123 kWh
4 months x 30 days x 5 hours x (4 x 20 - 4 x 4) = 38 kWh
Total 161 kWh of electricity saved @ 12.5 p/kWh = £20 saved.
However, in that 2500-hour period, probably most of the halogens would have blown at 2000 hour life, for a good-make lamp at £1:50 that's another £6 saved, for a total of £26.
That's nearly half the cost of the LEDs saved in 8 months. By the end of next winter the LEDs will have paid for themselves, and if the manufacturer's claims of a 25000-hour life are correct, still have another 20,000 hours of life left.
In 25,000 hours 1 x 4W LED will consume 100 kWh for a cost of £12:50. plus initial cost of the LED at £14:50, totalling £27:00
For 25,000 hours operation in one position 13 2000-hour-life halogens will be needed, at a cost of £20, plus energy consumption of 500 kWh or £62:50, for a total cost of £82:50.
Each LED over its life saves £82:50 - £27:00, or £55.50, and I have a total of 4 in this application, therefore saving £222:00 over the claimed LED lifetime.