We have had trouble with our contractor and electrician about spacing can lights. I think both of them need to watch this, thank you so much for providing the math!
I was hoping you'd cover how you chose the number of lights in the first place. Considering ceiling height, angle of flood light, lumens, etc. Placement is somewhat trivial, especially with the wafer lights (don't have to worry about joists). Also, that's just general downlighting. What about task lighting? For a kitchen, you don't want to just take the number of lights, distance between them and divide by 2. You'd want it a certain distance off the face of cabinets as a function of the height of the ceiling or flood angle.
@marsBWR Those are GREAT questions. I'm a DIYer, learning as I go along and sharing what I'm learning from my current project. Having said that, take a look at different rooms in different houses, and you'll will notice a high level of variability in distance between lights. How many you choose will depend upon how much light you would like in a space. The room I built this video about is going to be a Maker Space, so you are correct, something like a kitchen would have different needs and therefore potentially a different design. I'd suggest checking a few kitchens out and modeling what you see that you like in your own project.
