Recessed Lighting Placement Formulas

Recessed lighting placement calculations tell you exactly where the lights need to go on the ceiling.

In this tutorial, I will first explain how to manually calculate the placement for your lights, and then give you a calculator that does it all for you!

When spacing recessed lights, the distance between the lights is always double what it is at the ends. This formula, combined with the number of lights you have determined are needed, the lighting layout you have chosen, and the dimensions of the room or surface to be illuminated, is what we use to calculate the placement of recessed lights.

Note: Before you can calculate the placement, you need to know the layout for your lights.

Calculating Placement for General and Task Lighting

  1. Determine the desired “area” that is to be illuminated (It may be the whole room, a section of a larger room, or a work surface).
  2. Measure the length of the area and write down your answer.
  3. Divide the length of the area by twice (2x) the number of lights to be placed in that row and write down your answer. This will be the distance from the wall to your first light in that row.
  4. Double (2x) your answer from the previous step and write down your answer. This will be the distance between the rest of the lights in that row. So remember, the distance between your lights is always twice (2x) the distance from the wall to the first light.
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  5. Now do the same for the width of the area:  Measure the width of the area and write down your answer.
  6. Divide the width of the area by twice (2x) the number of lights to be placed in that row and write down your answer. This will be the distance from the wall to your first light in that row.
  7. Double (2x) your answer from the previous step and write down your answer. This will be the distance between the rest of the lights in that row.


Example: Room with 6 recessed lightsRecessed Lighting Placement

 

Calculating Placement for Accent Lighting

Accent lighting is somewhat of a broad term, so I’d like to clarify that this formula is specifically for calculating the placement of recessed lights that use adjustable trims for the purpose of highlighting a painting or object on the wall.

The optimal aiming angle to minimize glare is 60-degrees from the ceiling, so that will be the starting point. Don’t worry if the light cannot be placed at exactly 60-degrees, as sometimes it is not possible (or practical). Most trims have plenty of adjustment to compensate for various placements.


By using a trigonometric formula, we can calculate the ideal placement for your fixture(s).

In the side view diagram to the right, you will notice that the accent light, the wall, and the ceiling form a right triangle. This type of triangle is known as a “30-60-90″ right triangle.

Since we know the three angles of the triangle, and can measure the distance of side b (from the center of your object on the wall to the ceiling), all that we need to do is solve for the leg a, which will be the exact distance away from the wall you need to place your accent light to achieve the desired 60-degree aiming angle.

The rule for this special type of triangle is that the sides always have a ratio of 1 : 2 : √3.

Using this rule and the known side of the triangle (side b), we can use the following formula to solve for side a: Side a=(Side b√3)/3