Against the night sky in Redmond, Washington, U.S, an electrical transmission tower stands out in a surprisingly beautiful way. Thirteen rings of LED light encircle the tower, illustrating the sequence of the Kelvin scale, which expresses the color temperature of light: red at the bottom, moving through orange, yellow, warm white, then cool white and, finally, blue at the top.

  People become aware of the unreliability of non-LED lights, for they could not be re-used for next year. The lights will be displayed for 45 days, if using LED lights, statistics suggest that it will save about 12,000 kilowatts of power and $1,500 - approximately the amount of electricity an average family uses for one year. Besides, in 2011, the city planted a live tree in Tibbits Park to be used for years to come. In this way, buying a new tree each year is not becoming a must-have stuff, means it will save thousands of dollars every year. The annual City Lights...