Recessed Lighting Math That Actually Works
Walk into a room with poorly spaced recessed lights and you feel it immediately: bright spots on the floor, dark walls, uneven shadows that make the space feel uncomfortable without knowing why. Then walk into a properly lit room with the same fixtures, and everything feels right.
The difference is spacing, and the rules depend on whether you’re using 4-inch or 6-inch cans.
The Diameter Difference
Four-inch recessed lights produce a tighter, more focused beam. They’re better for task lighting, highlighting artwork, and accent applications. Six-inch recessed lights throw wider pools of light, making them better for general ambient illumination.
Neither is inherently better. The correct choice depends on ceiling height, room function, and your lighting intent.
Spacing Rules by Size
For 6-inch recessed lights with standard 8-foot ceilings, space fixtures 6-8 feet apart and 3 feet from walls. This creates overlapping light pools that provide even coverage without visible hot spots.
For 4-inch recessed lights, reduce spacing to 4-6 feet apart and 2-2.5 feet from walls. The narrower beam requires closer spacing to achieve the same coverage.
In both cases, the wall distance is crucial. Position lights too far from walls and you create dark perimeters that make rooms feel smaller. Too close to walls, and you wash the wall with light while leaving the center dim.
Ceiling Height Adjustments
Higher ceilings allow wider spacing. For every foot of ceiling height above 8 feet, add 6-12 inches to your spacing calculations. A 10-foot ceiling with 6-inch lights can handle 7-9 foot spacing successfully.
Conversely, lower ceilings require tighter spacing and often favor 4-inch fixtures to avoid overwhelming the space with light sources.
The Layout Process
Start by calculating the room’s square footage. For general ambient lighting, plan one recessed light per 20-25 square feet with 6-inch fixtures, or one per 15-20 square feet with 4-inch fixtures.
Sketch the room and mark center points for fixtures, maintaining consistent spacing from walls and between units. Adjust the pattern to avoid placing lights directly over furniture where they’ll shine in people’s eyes.
Then check your work: imagine circles representing light pools around each fixture. The circles should overlap slightly without leaving dark gaps between them.
Common Mistakes to Avoid
Centering a single recessed light in a room creates exactly one bright spot with darkness everywhere else. Always use multiple fixtures in calculated patterns.
Aligning recessed lights with windows places bright artificial light next to the brightest natural light, leaving the opposite side of the room dark. Instead, position recessed lights to illuminate areas that windows don’t reach.
Forgetting the trim angle creates glare. Use fixtures with proper baffles and position them to avoid sight lines from seating areas.
The Final Test
Before cutting holes, tape fixture locations on the ceiling at night. Stand in different parts of the room and evaluate the coverage. Adjust the tape until the layout feels balanced. Then cut and install with confidence.
Good recessed lighting is invisible. You notice the room, not the fixtures.
