Tonight I'm installing recessed lighting in my bedroom and have a question on how to space the cans. The room is 12' x '12. How many cans should I put in the bedroom and how should I space them?
There are a number of variables you need to consider in order to space them correctly.
First, how much light do you want? Brighter rooms require more lights. Related to this is the max wattage of your cans. You will need more 35W lights to achieve the same brightness you'd get with 50W cans.
What type of spread (angle of light ) do the bulbs you plan on using produce? Bulbs with a wider spread will cover a larger area but light will be more diffused.
The typical rule-of-thumb is 24" from each wall, and then 3-5 feet between cans. So in a 12' room you'd probably want two rows of lights. Considering it is a bedroom and you don't need it as bright as a kitchen, you can probably get away with 2 rows of 4 lights for a total of 8. If you are using 50W bulbs then you will have 400W of light in your room.
The height of your ceiling also plays a big role. Higher ceilings typically require more cans since the light diffuses more before it hits the floor.
Also take into consideration the position of ceiling joists; this might limit where and how many you can place.
I always recommend drawing out your design on graphing paper before you make your first cut. Find out the spread of your light (taking into account the ceiling height), and draw a circle under each can with a protractor. You want the light produced on the floor for each can to slightly overlap another light so that thre are no dead spots.
Make sure you check the ceiling joists before you start cutting!
I should also mention that if you are installing into an insulated area, make sure you use IC (insulation contact) rated cans!
For a bedroom, you probably dont need as much light as you might want in a room where there is more activity going on. So you probably only need about 2 or so lights. However, that might looks a bit odd, not sure where you would place them in a square ceiling.
So you best bet might be to use 4 lights, symmetrically placed and centered so it makes a smaller square. Probably a 6x6 with 3' around the outside or perhaps a 5x5 square with 3.5' around the outside. You could even do 4x4, but that might put too much light in the center of the room.
With 4 lights though, assuming you use 60W floods, you will certainly want to use a dimmer on that.
General answer. See last paragraph for bedroom specific
Best I can find for a room of that size is 3-5 feet spacing. and about the same for the distance from the wall. -- Keep in mind that this is for a living space, not a bedroom.
Based on a 12x12 Living or Dining room, I'd go with 3 ft spacing, for a total of 9 lights at (3,3),(3,6),(3,9), (6,3),(6,6),(6,9), (9,3),(9,6),(9,9)
IFF it's the only light in the room.
If it's too bright, reduce the wattage.
It also depends on other factors. If you have a large window, or plan on using floor lamps or reading lamps, then I'd reduce it to two rows of three at 4' spacing.
Alternatively, you may want to put in extra switches, controlling each row of 3 independently.
For a bedroom, I'm going to assume there are reading lamps, and for much of the time you're going to be in bed with the lamp on, and the pot lights off. In this case, I'd go with 4 lights at (4,4),(4,8),(8,4) and (8,8) With the proviso that you don't want a light directly above the head of a sleeping person. Also, put it on a dimmer.
If your bedroom has a traditional sliding-door style closet (as opposed to a walk-in, which would have it's own lighting), you may want to put extra lights immediately in front of the closet doors to make it easier to view into the closet. As a bonus, that way someone standing there to pick out clothes isn't casting a shadow on what they're selecting.
In fact, in my childhood bedroom (approximately 12x12), the wall switch controlled only two recessed lights in front of the closet door (the type that angled towards the closet). That provided enough light for the rest of the room in most situations, and reading/desk lamps provided additional lighting when tasks required it.
Steven's answer is pretty helpful, but there's some additional useful information on eHow: http://www.ehow.com/how_12018871_calculate-recessed-lighting-spacing.html