Saving energy by changing lighting
Lighting is good place to start improving energy efficiency; you can get quick and easy savings by changing bulbs (called “lamps” by lighting professionals). Lighting commonly accounts for 20% of residential energy use and 40% of commercial use. It is common to save 20-50% on electricity for lighting changes (i.e. 4% to 20% of the total utility bill). A common house uses 2000 kilowatt-hours (kWh) per year on lighting if it has all incandescent lamps. Changing to half compact florescent (CFL) or LED lighting would reduce that by 60%. At a typical utility rate of 15 cents/kWh, that would be a savings of $120 per year.
Lights generally use the wattage they are listed at, although they vary some. I measured 60W incandescent bulbs from 59W to 63W, florescent lights very close to listed power, and LED lamps using 10 to 20% more power than listed. The brightness also varies, with LEDs typically appearing significantly brighter than advertised. For example, a 13W LED with labeling indicating that it produces 800 lumens and is equivalent to a 60W incandescent bulb is actually bright enough to easily replace a 75W incandescent bulb. But watch out, many cheap import off-brand LEDs use false advertising and do not produce the light advertised. If you stick with brands like Phillips and GE you should be OK. CFLs also tend to out-perform their listed brightness.
Dollar savings shown for lamps are usually based on being on for 3 hours a day, so lights in main rooms or halls can have greater savings, but lamps in rarely used places like attics are not worth changing. At 3 hours/day, a 60W bulb costs $9.85 to power for a year, but an 11W CFL replacement only costs $1.81 to power, so you save $8 a year by switching that single bulb. A light that stays on all night would have much higher savings, as much as $32 a year, but changing a light that is only used a few minutes a day would not even save a dollar. Changing larger lights, such as 100W bulbs, will produce larger savings.
There are additional benefits to changing lights. CFL and LED lights have much longer life than incandescents, so once you put them in you can forget them for years. Different CFL and LED lights produce a variety of color qualities, so you can choose lighting to suit your taste; for example getting close to natural lighting. Inefficient lighting generates heat that can be an issue in the summer. When air conditioning is being used, think of the wattage of the lamp as being doubled: once to produce the light and then once more to remove the heat from it.