Earth Hour - Australia wide - more or less - Mar 29 8-9pm.

www.earthhour.org

I won't be bothering to turn any lights off for just one hour in that time, as for the last 20 years I have

1) used CFL lamps
2) used a minimum of lights & other appliances all the time
3) done things like turn off the hot water heater when away for more than a day or two....

etc