Standard 100W light bulbs cost 40p each and are expected to last for 2 years in average use. Low power equivalent brightness bulbs cost £10 each, are expected to last for 8 years and use only 20W. A 100W lightbulb operated for 10 hours will use 7.5p of electricity. A 20W bulb will operate for 50 hours on the same amount of electricity. I have a light in my living room which is on for about 20 hours per week. Next time the living room bulb breaks, I will buy a low wattage bulb instead of a standard one.