Last Saturday 28th March from 8:30 to 9:30, about two thousands students organized a flashmob and a street parade in Gwanghwamun and Seoul plaza in Korea for the international project "Earth hour" to prevent climate change. The "Earth hour" is international environmental campaign of World Wide Fund for nature(WWF) which aim is to switch off the lights once a year for 60 minutes. It started first in Sydney, Australia and is widely spread to 162 countries and over 700 cities with the participation of persons, companies and organizations in 2014. Among cities as the main landmarks, there are Harbour Bridge in Sydney, Opera House in Sydney, Sky Building in New zealand, Big Ben in England, Eiffel Tower in France, The Great Wall in China, Tokyo Tower in Japan, Namsan Tower in Korea and the National Symphony Orchestra in Washington, U.S, etc. As the main companies, there are Starbucks and Coca Cola. This latter participating "Earth hour" campaign and even spreading the need of this campaign through street parade or online event. We all live without knowing the preciousness of lights because we can use electricity easily. Every Saturday of the last week of March a year, all of us can save energy of 692 million kWh, decrease three thousand 131t of CO2 in order to get the effect of planting over 629,640 young Pinus tree by participating actively in this campaign. Let's give a comfortable rest to our precious Earth by joining this campaign during only one hour that is not too short but also not too long.