For cooling, the fan's direction of rotation should be set so that air is blown downward (Usually counter-clockwise from beneath, but dependent upon manufacturer). The blades should lead with the upturned edge as they spin. The breeze created by a ceiling fan creates a wind chill effect, speeding the evaporation of perspiration on human skin, which makes the body's natural cooling mechanism much more efficient. Since the fan works directly on the body, rather than by changing the temperature of the air, it is a waste of electricity to leave a ceiling fan on when no one is in a room unless air conditioning is in operation.