The UN will observe Earth Hour March 31 by turning off the lights for one hour at its facilities around the world.
The world body, headquartered in New York, will join scores of other landmarks around the globe that are participating in the Earth Hour event.
Earth Hour, launched in 2007 in Australia by the World Wide Fund for Nature (WWF), which is a global conservation group, calls on people, organisations and cities to turn off their non-essential lights for one hour starting at 8.30 p.m. local time.
This is the third year that the UN joins hundreds of millions of people around the world in switching off the lights, Xinhua reported.
UN Secretary-general Ban Ki-moon said the UN was turning off its lights "in solidarity with the men, women and children -- 20 percent of all humankind -- who live with no access to electricity".
Calling Earth Hour "a symbol of our commitment to sustainable energy for all", Ban said: "We need to fuel our future with clean, efficient and affordable energy."
"By acting together today, we can power a brighter tomorrow. The United Nations is strongly behind this cause from Earth Hour to Rio+20," the secretary-general said, referring to the UN Conference on Sustainable Development slated for June in Brazil.
In 2011, more than 5,200 cities and towns in 135 countries worldwide switched off their lights for Earth Hour to show support for action on climate change.
The Earth Hour event takes place about one week after the vernal equinox -- when night and day are of the same duration in both hemispheres, ensuring that it will be dark everywhere in the world at 8.30 p.m.