Every year hundreds of thousands of people put up christmas lights. If you look at the package, the average string of christmas lights uses about 500 watts of electricity per hour. Once you add multiple strands of lights and you leave them on for a couple of hours, you're looking at using something like 10kW*hours per day to operate christmas lights. This is a lot.

Of course the easiest way to save this energy is to not put up lights. But if you're really set on having christmas lights there is better, greener, solution available: LED christmas lights. They take 1/10 the electricity of ordinary christmas lights and they last longer too. While they are more expensive to purchase upfront, the significant savings in electricity used will have you breaking even after tow years. After that you're actually saving money. And of course all along you are using less electricity which is better for the environment.