How does the code address permanently installed sighting circuits? Do you supply for the rated maximum of the fixtures or to the load you are going to install?
I'm installing 32 recessed can lights in the 16' x 42' "attic" over the shop. The cans are rated for 75 watt incandescent bulbs. If you use the 75 watt value You need a feed capable of supplying about 3000 watts.
My plan is to utilize LED lamps. Load is about 13.5 watts per lamp. That drops the calculated load down to aboy 500 watts. 3000 watts at a minimum requires 2 15 amp branch circuits, more likely splitting the load between a 15 amp and a 20 amp circuit.
500 watts and thatch well within the capability of the 15 amp circuit that's already there for the stair lights.
My thoughts are that within the next 5 years or so you won't be able to buy incandescent 75W bulbs. Hard enough to find now as it is. Not going to worry about me, I know I won't put any thing but LED's in there and the first set will probably be the last set I'll ever have to concern myself with.