This is in a two story, ~1000square foot per floor building. With the advent of affordable, decent (IMHO) LED fixtures (finally!) the entire lighting load for the structure looks to be 500W – 1000W at the outside – well below even the 1440VA that a paranoid or cautious soul might derate 15 amp lighting circuits to on the basis that they are (at least potentially, in the long dark winter) pretty much like a continuous load. Great news for my power bill.
There will be NOTHING but lighting on the lighting circuit (or circuits.) I've been on the other side of that, not going back. I have never personally seen a lighting-only circuit blow, though I'm sure it must happen – very occasionally. These are lights in the ceiling, not outlets/receptacles that could have "whatever" plugged into them.
Do I need to split lighting into several circuits to satisfy a code requirement, or not?
I may anyway, to ease the wild hare of "I suppose the lights could trip a breaker" but is there a code-driven need to? As far as I can see, from a practical point of view, all the lighting needs of my building in the modern age can be met with a single 15A 120V breaker.
Say, for instance, the one lighting one light at the panel right now. (which I've given a separate question.)
If you want to get picky about edition, I believe that 2011 NEC is the currently adopted code for the USA location.
Best Answer
As far as the NEC is concerned, there is no limit to the number of outlets (lighting outlets in this case) that are allowed on a single circuit assuming that the attached fixtures don't exceed the rated capacity of the circuit.
However, @Edwin raises exactly the correct point in the comment - what matters is what the fixtures are rated for, not what they are currently being used for. The general rule of thumb that electrical inspectors tend to use is around 8 boxes for a 15A circuit and 10-12 for a 20A circuit. Keep in mind that they are counting boxes, not what gets put into them. The idea is that you can put in a receptical rated at 5W, decide you don't like it, and throw something with a 150W load in the same receptical. The only thing that makes something a "light" in the eye of the inspector is that it is on the ceiling and has a switch running to it.
Outside of the load consideration you actually bring up a good point in the question, which is safety. While the NEC doesn't specify a minimum number of lighted branches (other than the panel lighting requirement), your local authority very well could. I know my jurisdiction only allows 2 rooms to share the same branch for lighting purposes, precisely for the reason you mention - you pop a breaker, you're in the dark.