I'm trying to determine how many recessed lighting fixtures I'll need to light an area that is a 500 square foot rectangle, with 30 lumens per square foot (30fc). 30 lumens per square foot is what is recommended for the type of room in question, but the recommendation guides don't say what height those recommendations are intended for.
In my case, 30fc times 500 sqft would be 15,000fc total.
An R40 compact florescent lamp has a rating of 1150 initial lumens (at the fixture). Looking at photometric data though, it appears that this lamp produces 1fc at a 12' height with a 37' spread.
So, if 30fc is the goal for the room, do I want 12 fixtures, which will produce 30 lumens per square foot near the ceiling? Or 30 fixtures to produce 30 fc at the floor? Or something in between?
Or to put it more succinctly, when guides recommend that such and such a room should be x lumens, do they mean initial lumens at the fixture, or lumens at the floor, or lumens at the expected working height (like a counter top)?