Part A: How many pot lights do I need?
Step 1: Measure the length x width of the room. Now you have the area or total square footage of your room.
Step 2: Multiply the area x 1.5 = total wattage. (Note in some areas where you need a lot of light, or have a very high ceiling multiply by 3). If the lights will be installed in a ceiling taller than 16-feet, you may also want to use PAR type light bulbs. They have a tighter beam control which will get more of the light down from the ceiling to the surface plane.
Step 3: Total wattage, divided by the bulb wattage you plan to use, ie. (60 watt, 100 watt) = amount of total recessed lights you will need.
Formula: total sq. footage x 1.5 = total wattage needed. Total wattage divided by 60 or 100 watts = total amount of recessed can lights.
Example: 240 square foot room x 1.5 = 360 divided by 60 (the bulb wattage I'd like to use) = 6 recessed lights.
Part B: Draw up a ceiling diagram (reflected ceiling plan) showing the amount of lights you need (Part A formula). The cans / pot / recessed lights should be evenly distributed around the room, usually they are in rows with an equal number of cans in each row. Here's a great example:
Part C: Light spacing in a row:
Step 1: Pick a starting point, where do you want your most important light placed? Then arrange all the lights an equal distance from that light. Or, if you want general lighting, start in the middle and work outwards.
Step 2: Measure the length of the room in feet.
Step 3: Room length divided by # of lights in that row = distance between light units in that row. Example: 20' long room divided by 3 cans = 5' between each light.
Step 4: Calculating distance of lights from walls: (Note: The can lights near the wall are 1/2 the measurement between the other can lights distance in the middle of the room. Keep each light close to 3 feet away from the walls or corners - we don't want to cast shadows!) Don't install recessed lighting with equal spacing between the lights and the walls. If you do, you end up with bright spots between the lights and dark edges.
Step 5: Now do the same for the width of the room.
Task lighting is extra lighting used to highlight spaces where you need either extra light, or specialized lighting.
You may want to add under cabinet lighting, or pendant lights over the island to bring the lighting closer to the work area.
How to calculate the distance and spacing for task lighting:
Step 1: Determine the distance from the ceiling down to the surface you wish to light, ie. the floor or a countertop.
Step 2: Divide this distance by 4 to obtain the distance from the wall to the first light unit. Ie. 8' ceiling lights should be placed two feet away from the wall.
Part E: Wall washers recessed lighting layout: (lighting that shines down onto a wall in order to highlight art or a wall feature)
Step 1: The rule for installing wall wash recessed fixtures is approx. 1.5' to 3' away from the wall.
Step 2: Fixed lights can be placed closer to the wall.
Step 3: Place adjustable lights farther away from the wall. The optimal aiming angle to minimize glare is 30-degrees from the ceiling, that way we avoid glare.
Step 4: Space wall wash fixtures the same distance from each other.
Step 5: A good rule of thumb is that your accent lighting should be 3 times brighter than the ambient light in the room.
Part F: Beam Spread
There are generally 2 types of recessed lights - Spot lights and Flood lights.
Spot lights have a narrow beam of light casting light to a focussed area, usually these are used to highlighting art or important design elements in the room. They cast beams 45 degrees or less.
Flood lights case a wider beam on the floor area and are used for lighting larger, more general areas. They cast beams up to 120 degrees.
Lighting Beam calculation: Angle of beam x 0.18 x ceiling height = Beam spread
Example: 60 degrees x 0.18 x 10' ceiling height = 10'8" wide beam spread.
To create overlapping beams of light for ambience, make sure that your beam spread diameter is equal to or greater than the distance between light sources fixtures.
Recessed lighting installation:
Now that the recessed lighting placement locations are determined, we need to find out if they can be installed in these locations. Use a stud finder to determine where the ceiling joist are located. You might have to adjust placement locations to avoid hitting a ceiling joist. It's always best to pre plan the lighting design before your renovation or new build.
Please remember to contact your electrician before making any electrical decisions.