Cost of Christmas Lights

A friend of my had a concern as to the cost to keep the Christmas lights on during this holiday season. As it so happens, I have a specialty in electrical systems. So, how much does it cost?

Let’s assume 5 strands of 150 lights each, for a total of 750 lights. We’re going to be old school and use the regular “white” Christmas lights, not LED’s. Christmas lights use “about 25 watts per 50-bulb strand”12. 750 lights is electrically equivalent to 15 50-bulb strands, or  15 \: \text{50-bulb strands} \times 25 \: \text{watts} = 375 \: \text{watts}. The base rate for electricity in Seattle3 is 3.86¢4 per kWh5.

Thus,  375 \: \text{watts} \times \frac{1 \: \text{kW}}{1000 \: \text{watts}} \times \frac{24 \: \text{hours}}{\text{day}} \times 60 \: \text{days} \times \frac{\$0.036  }{\text{kW} \times \text{hour}} = \$19.40

Remember, that’s if you left the lights on all the time for two straight months. If you left them on for 8 hours a day instead of 24 hours, that would be $6.48.

Similarly, if you only used 2 strands of 150-bulbs each for 8 hours a day, that would be $2.59.

Or, if you used 2 strands of 50-bulbs each for 8 hours a days, that would also be grand total of 86.4 cents.

Point being, it doesn’t cost all that much to run your Christmas lights. It costs an order of magnitude less if you use LEDs, which use about 0.05 to 0.07 watts per a bulb. Move the decimal one place to the left on the above costs and you have a pretty good idea of what it costs to run an equivalent6 LED string of lights.

And that’s how engineering works, folks.

NB: I’m experimenting with using \LaTeX to display equations. It’s really quite spiffy.

  1. HowStuffWorks 

  2. GreenOptions reports consumption for each mini-light at about 0.5 to 1 watt 

  3. http://www.seattle.gov/light/accounts/rates/docs/2009Oct_rsc.pdf 

  4. assuming you’re a residential user and use less than 16kWh/month 

  5. kWh is a funny measurement and is actually not time based. For example, a 100 watt bulb that is on for one hour uses 100 watt-hours of energy. Similarly, a 100 watt bulb that is on for 30 minutes uses 50 watt-hours of energy. 

  6. by number of lights, not output of light 



The 787 will make its official public debut in a couple days on July 8th, 2007 (that would be 7/08/07). It’s going to be pretty spectacular.

If you haven’t had a chance yet, you should take a look at NewAirplane.com and then click on the “Launch 787 Dreamliner Site” button. A video has been released every day since last weekend showcasing a different aspect of the new 787.

There is some really cool stuff going on.

Everybody knows that the 787 is the new composite-fiber airplane.

But there is so much more.

Some of my favorite features include electronically tintable windows, sawtooth pattern of the engine chevron makes for a quieter flight, the main cabin is pressurized to 6000 feet (compared to 8000 feet of current airplanes), LED lighting that can emulate earth cycles, huge windows sizes, and so much more.

I’m having a 787 launch party at my house if anyone is interested. Show up around 3pm on Sunday. The fun starts at 3:30pm local time!

Save: Buy Boeing / Buy: Save Airbus“: © Chappatte/International Herald Tribune, Jun 22, 2007