I needed a Dawn to Dusk sensor switch that auto turns ON during the day and OFF at night. I bet someone will know how to reverse the existing Dusk to Dawn sensor switch which is readily available.
The simplest way to reverse action of a switch is to change from NO(normally open) to NC(normally closed) contact, or vice-versa ..
If you have a dusk-dawn switch, try to investigate whether the relay inside has both options, and if yes, simply change wires from one contact to the other ..
If you havn't got a dust-dawn switch yet, here is an example of such a device .. http://www.geocities.com/tjacodesign/duskdawn/duskdawn.html
Just remember to select a relay that has change-over contacts .. see picture below ..