Retrofitting existing floodlights

["cmc" <colinmc@xxxxxxx>]

As a newbie to the world of home automation, I have what may be a basic
question.

In back of my home I have three dual floodlights (with two 75w lamps in
each) which are switched on and off at a switch inside the house.

Is it possible to add a motion sensor to the system so that these
floodlights would become "security lights". If so, what would I need to
purchase and could I, with my minimal skills, do the installation
myself? Would I replace the exsiting switch with something else?