Last year it was estimated that more than 5,200 cities and towns in 135 participated in Earth Hour by switching off lights for an hour. Homes, businesses and public departments took part. The idea is to send a message to each other and those with the power to make changes to think about the environment and our impact upon it.
It doesn't take a lot - to flick a switch - but you could always practice tonight, and tomorrow just to make sure you get it absolutely right on Saturday at 8.30pm.