You replace a 40 W incandescent lightbulb with an 8 W LED bulb. If you leave your lights on 24 hours a day, how much energy are you saving each day by replacing this bulb?
You're saving (40 - 8) = 32 joules every second. During the 86,400 seconds of a whole day, you've saved 2,764,800 joules. That's durn near 0.768 of a kilowatt-hour.
