How green is your tree? LEDs vs incandescents

We probably all know by now that LEDs use about 80 per cent less electricity than incandescents, but how much difference will it make to your personal carbon emissions?

To give you an idea, I'm going to look at the carbon emissions from my own Christmas tree. There's going to be a lot of numbers, and just as much math, here (but no calculus, I promise). But it will be worth it, because at the end we'll get to compare how switching up the lights on your tree compares to limiting the amount you drive your car.

OK, here's my tree. It has 450 lights on it.

A single incandescent minilight uses about 0.408 watts.

A single LED bulb uses about 0.069 watts.

Now I need to multiply both those numbers by 450.

• Total incandescent wattage: 0.408x450=183.6 watts
• Total LED wattage: 0.069x450=31 watts

A bit of science next. We need to figure out how many kilowatt-hours I'm burning. A kilowatt is 1,000 watts, and a kilowatt-hour is a kilowatt burning for one hour.

Kilowatt-hours are what you arecharged by the power company.

Unfortunately, I don't make a habit of measuring how many hours in the day the tree lights are on. I'm going to have to make a guess, and I'm going to say six hours a day. I'll multiply that by how long the tree is up, usually about three weeks.

• 6x21=126 hours

Next up, total energy use for the season. We multiply the kilowatts (remembering to divide the number of watts by 1,000) by the hours.

• Total incandescent energy use: 0.1836x126=23.1 kWh
• Total LED energy use: 0.031x126=3.9 kWh

To calculate what that means for carbon emissions we need to know how much carbon comes from producing a kW/h of electricity. We don't have numbers for P.E.I., but Environment Canada reports average carbon emissions for electricity generation in Canada in 2013 were 150 grams per kWh.

So:

• Total carbon emissions for incandescents: 23.1x150=3,465
• Total carbon emissions for LEDs: 3.9x150=585

That gives us a potential carbon saving of 2,880 grams, just under three kilograms, for the season.

What about the car?

Yes, yes, now, as promised, the comparison to driving the car.

Burning a litre of gas produces 2.3 kilograms of carbon dioxide, so we're talking about the equivalent saving of 1.25 litres of gas. How far that will get you will depend, of course, on what vehicle you're driving.

But that's just you. Remember, keeping carbon out of the atmosphere is a community effort. There are 62,000 households on P.E.I. If 30,000 Christmas trees are converted to LEDs, that saves more than 86 tonnes of carbon, the equivalent of not burning almost 40,000 litres of gasoline.

A reasonably energy-efficient car will take you 10 kilometres on a litre of gas, so that saving is roughly like not driving from one end of the Island to the other 1,460 times.

That's the thing about numbers. Even small ones can add up quickly.

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