[Neil]

The large 500w floodlights are over powered for a lot of security applications, especially if we are only talking about a smallish back yard. You should find that the smaller 150w halogens flood lights are ample for that. My back yard is an 'L' shape so I have 2 150w halogens with PIR's at about 7 feet high with the lamps pointing low. This gives ample light without annoying the nieghbours. Set the on time to only a couple of minutes and you will save a lot of electricity compared to the 500w halogens with long on times, like most are set.