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Let's start with the most ubiquitous mobile device—the cell phone. What happens if you leave yours plugged in all night? According to measurements from Lawrence Berkeley National Laboratory, the average cell phone draws 3.68 watts of power from the outlet while it's charging and 2.24 watts when charged. Let's take the worst-case scenario and assume that you're over-juicing a charged battery for the entire night. Leave the average phone plugged in for eight unnecessary hours, and it'll use about 0.018 kilowatt-hours of electricity. Do that every night for a week, and the figure rises to 0.13 kWh; every night for a year, and you're looking at a grand total of 6.5 kWh of electricity.

Given that the average American's residential electricity consumption is more than 4,000 kWh each year (PDF), the Lantern doesn't think that a handful of kilowatt-hours are worth much tossing and turning. You could do way more for the planet, for example, by swapping out a single incandescent light bulb in your home for a compact fluorescent one; as the Lantern pointed out in a previous column, that simple action alone can save 126 kWh a year. Plus, charging your gadgets while you sleep has the added benefit of shifting a tiny fraction of your energy usage from the daytime, when demand is highest, to the nighttime, making things just a bit easier on your local grid.