New Delhi, July 31 - Historical monuments, several government buildings and many households turned dark Friday evening as Delhi voluntarily switched off the lights for an hour to save power and become environment friendly.

Exactly at 8.30 p.m., the Delhi secretariat, old secretariat, Humayun's Tomb, the Archaeological Survey of India building and several other government offices went for a voluntary blackout, abiding a call from Chief Minister Sheila Dikshit to save power.

The initiative comes on the lines of a global Earth Hour observed March 28 when Delhi managed to save a whopping 10,000 MW of power in an hour. Taking a cue from the event, the Delhi government decided to observe Earth Hour quarterly - on the last working day of every third month.

The government had asked 2,000 residents welfare associations (RWAs), 2,000 students in school ecological clubs and market associations to join the campaign.

'Yes, we switched off the light to be a part of the green and meaningful campaign,' said Ravi Singh, a director of WWF-India.

'This is a great initiative by the state government and we will cooperate with them as much as possible,' he told IANS.

While calling for the voluntary blackout, Dikshit had said: 'You did it for an hour in March, saved 1,000 MW, a world record.