Originally Posted by ceclmc
You can load a circuit up to 70% continuous load. The number of lights is really not important as long as you size the circuit accordingly. It works out that way for receptacles also. You have no control over how many things someone will plug in to them you just have to size the breaker and wire correctly so that it doesn't present a fire hazard. Just as you cant control what size light bulbs someone installs, you have to size the circuit so that the breaker will protect the size wire that you install. A 15 amp breaker and #14 wire should work nicely for your project. You will not exceed the 70% continuous load.
First off, it is 80% in the US for a continuous load, not 70%. Also, in a residence, receptacles and lighting are taken into account in the demand load calc. There is NO limit to number of lights or receptacles on a circuit.
That said, if you have a circuit with many lights it is obviously a good idea to size it according to the amount of lights that will be used at the same time.
Outdoor or security lighting are some of the few things in a residence that would actually be considered a continuous load.