Edison made the first public demonstration of his incandescent light bulb on December 31, 1879 in Menlo Park. It was at this time that he declared: "We will make electricity so cheap that only the rich will light candles." Now many citizens can afford to use a light bulb during the night and can enjoy any type of entertainment at night through the light bulb. Nowadays, there are more than 500 billion electric lights around the world decorating the Earth at night. The number of lights at night is a standard for measuring whether a country is developed or not. For example, in South Korea, light covers almost the entire country, while North Korea has a few in the capital. The Internet is another practical use of electricity since users must use electronic devices to browse the Internet. Internet connects the world and sends the message in seconds. In the past, traveling and meeting people were difficult, and people wrote letters and books to exchange ideas and thoughts. Using the Internet, people can use email, blogs, Twitter, Facebook, and they can use the +visible system to communicate "face to face" with people who are miles away via the Internet without leaving