Re: 6" recessed light layout help
For whatever light source you are using, you should be able to get a spec for either a spread angle or a coverage area for a given lamp height.
Using this information, and knowing how high your particular lights will be, you should be able to calculate coverage patterns for your floor area.
A rule of thumb is to overlap each coverage pattern by 50% -- that is, if a fixture covers a 10 foot wide circle you want your fixtures 5 feet apart. Otherwise, you will have significant light/dark gradients.
Keep in mind that as your fixture is raised, the circle spreads, but it also gets dimmer. The way to combat the dimness is to NOT increase the spacing to match the circle spread as you go up, but to maintain the spacing. So if an 8' ceiling suggests placing the cans 6' apart, by maintaining that spacing as the ceiling height increases the illumination level should remain about the same*. The effect is that the overlap might be 80%, cancelling out the dimming effect.
* You may have heard about the "inverse square law" which states that from a focal point, as the distance doubles, the illumination decreases to 1/4. (Or as triples, to 1/9.) This doesn't really apply to your situation, because you will be using a reflector or focused source; the effective focal point isn't at the light itself but several feet above it. With an array of lights, the effective focal point can be tens or hundreds of feet above, meaning that you can move the array several feet without noticing a commensurate decrease in luminosity.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.