Strands of lights are ubiquitous this time of year — tangled in leafless trees, framing windows, sparkling their way to Santa’s sled. They are a beaming reminder of both the warm feelings of the holiday season and the environmental costs of this time of hyper-consumption. In 2003, a paper published by the Department of Energy estimated that holiday lights accounted for 2.22 terawatt-hours of energy use per year in the United States, which roughly equals the energy consumed by 200,000 homes annually. With numbers like that, coal may be the best thing to stuff in your neighbor’s twinkling stocking. He may need it.
Fortunately, Christmas lights have gradually switched over to LED in recent years. They are up to 90 percent more efficient than old-fashioned incandescent bulbs. So, should you trash your old holiday blinkers for their LED counterpart?
From an environmental perspective, it’s rarely advisable to discard something that works and replace it with an energy-efficient version, since the energy required to produce your new bauble is often greater than the savings it offers once you use it. It wouldn’t make sense, for example, to trash a perfectly good sedan to buy a new Toyota Prius: Producing a car takes a lot of energy, and hybrids are only about twice as energy-efficient as conventional engines.
Holiday lights, however, are an exception to the rule. A new strand of LEDs will last four or five decades, possibly the rest of your life, depending on how long you leave them on (and how long you live). They’re also less likely to start a fire, which is important when you’re wrapping them around a bundle of kindling like a Christmas tree. If you’re still harboring an old strand of incandescent lights, the Earth begs you to ditch it and go for the LEDs. (If it’s one of those multicolored, flashing strands, your neighbors would probably second the motion.)
Of course, there are more extreme options for electricity grinches. When I was a child, my favorite tree adornment was a string of popcorn. Making such a thread is a fun family activity, and you can sneak a few kernels for yourself in the process.
Is it greener than a strand of lights, though? To make this comparison, we’ll have to make some assumptions.
It’s hard to say how much embedded energy is in a strand of Christmas lights. However, since the lights will last 40 or 50 years, that embedded energy comes very close to zero on a yearly average. The only energy we have to attribute to the lights is the electricity, which, for a strand of larger LEDs, is 2.5 watts. If you run them four hours per day for 30 days, that means 0.3 kilowatt-hours over the course of a season. According to EPA conversion data, generating that much electricity would emit 0.44 pounds of greenhouse gas equivalents. (A carbon dioxide equivalent is all the greenhouse gases emitted, expressed in terms of the global warming potential of carbon dioxide.)
Now for the popcorn. There’s very little popcorn-specific environmental data, but the variety of corn commonly grown for popping is closely related to the corn used in cornmeal. So if we just use generic corn data, our estimates will be close enough.
According to researchers at the University of Massachusetts, cultivating an acre of corn generates approximately 1,700 pounds of greenhouse gas emissions. The average farm produces 155 bushels of corn per acre. Since a bushel of shelled corn weighs approximately 56 pounds, there are around 0.2 pounds of greenhouse gas equivalents embedded in a pound of corn by the time it leaves the farm gate. For most foods, transporting, processing and cooking account for slightly more than the amount of greenhouse gas emitted during cultivation and harvest. So let’s say a pound of popcorn — which is probably enough to trim a medium-size tree — would result in the production of just under a half-pound of carbon dioxide equivalents.
In other words, from an environmental perspective, there’s very little difference between trimming your tree with a pound of popcorn and using a strand of LED lights. That may seem surprising, since natural, farm-raised popcorn just feels greener than manufactured lights.
But details make a difference. Old-fashioned incandescent lights would be far, far worse for the environment: They use 10 times as much electricity as LEDs and don’t last nearly as long. You’ll also need to store your LEDs properly and turn them off when no one will see them anyway. Of course, if you have a few extra lights, you can’t eat the leftovers.