Hey there, time traveller!
This article was published 14/12/2013 (1135 days ago), so information in it may no longer be current.
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 the warm feelings of the holiday season and the environmental costs of this time of hyper-consumption. In 2003, a paper published by the U.S. Department of Energy estimated 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.
Fortunately, Christmas lights have gradually switched to LED in recent years. They are up to 90 per cent 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 harbouring an old strand of incandescent lights, the Earth begs you to ditch it and go for the LEDs. (If it's one of those multicoloured, 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 favourite 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 about 200 grams 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.
According to researchers at the University of Massachusetts, when you crunch the numbers, the greenhouse gas emissions from growing, harvesting and transporting the roughly 500 grams you would need to trim a tree would generate about 230 grams 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.
-- Washington Post-Bloomberg