The specially designed stamps feature an owl, a possum and an orang-utan and carry messages to conserve energy. Australia Post expects to sell several hundred thousand of them.
This is the third year of Earth Hour, an event organised by WWF Australia in conjunction with Fairfax Media. It has grown from 2.2 million participants in Sydney in 2007 to an estimated 50 million in 35 countries last year.
This year it hopes 1 billion people will switch off and send a strong message to politicians who will meet in December to thrash out a successor to the Kyoto Protocol.