When you switched off for Earth Hour and lit a candle, did you stop to think whether you were emitting more or less carbon than before? The answer turns out to depend on how many lights you switched off and how many candles you lit.
A 27g candle provides 3 hours of light. Calorific value of wax is the same as butter, right? About 3kJ/g. So burning a candle uses source fuel (wax) at the rate of 7.5W. Four candles, 30W. About the same as 1 10W CFL bulb (assuming electricity is generated from fossil fuels with about 30% efficiency). [edit 2009-03-31: massive blunder: not 3 kJ/g but 30 kJ/g, making four candles equal 10 CFL bulbs. See later correction article]
So if you switched off your dining room light and lit 4 candles for dinner, you were carbon neutral [edit: no, it’s all wrong, see later correction article]. 4 candles is a pretty romantic light level, way way less than your 10W CFL will give.
Only slightly relevant observation: candles can be made sustainably, at least in principle, from beeswax, soy, and tallow. But if you think that lighting your house with organic soy candles is somehow promoting a sustainable lifestyle, you’re way off base.