From a true security standpoint, motion lights are not the best solution compared to always-on lighting. The overwhelming response from *actual burglars* when questioned about such things is that they avoid well-lit areas at all costs. I have personal experience with that. The motion-sensing version does not provide that initial reaction. and they are often able to be avoided if carefully approached.
That being said, a trip to your area electrical lighting supply house would be in order. Much better quality stuff than Lowes Depot etc, and you can talk to a real-live person which can actually answer questions about your concerns.
I agree with mattmag on going to an electrical lighting supply house.
I offer this as a thought only....what about a two stage deterrent. What about a dusk to dawn light (possibly bug light) and then adding motion light. With some always on lighting you get some security vs total darkness luring the bad guys in close. With two stage there is an awareness that there is some lighting and the they get the big search lights if they get too close. Just a thought....