Recessed Light Calculator

What it is

Recessed Light Calculator helps you estimate recessed light count, spacing and placement in a rectangular indoor room. Enter room dimensions, choose room type and fixture specifications, then the tool uses a simplified lumen-method estimate to calculate maintained average illuminance. The calculator generates 2D layouts with heatmaps and beam coverage visualizations. Results can be exported as PNG plans or CSV coordinate data. The tool is designed for homeowners and anyone comparing a first layout before discussing details with an installer or lighting designer, not as a professional lighting-design review or installation specification.

Questions from the bench

How many recessed lights do I need for a 12 × 12 ft room?

With the calculator's current example settings, a 12 × 12 ft room needs 6 recessed lights in a 3 × 2 grid using an 8 ft ceiling, floor-level calculation plane, 13.94 fc target (150 lux), and 850-lumen, 90° fixtures. The estimated average illuminance is 15.58 fc (168 lux) with 6 ft spacing across the width and 4 ft along the length. Different brightness targets, fixtures, or calculation heights can change the result.

Can I calculate a layout for LED recessed lights?

Yes. Enter the total lumens and beam angle from the complete LED fixture's packaging or specification sheet; wattage is optional. Choose a listed, source-checked model or enter custom specifications. A housing model or the word LED alone does not establish light output.

How far apart should recessed lights be?

For general room lighting, start with about half the ceiling height. With an 8 ft ceiling, that means approximately 4 ft between lights, measured center to center.

How far should recessed lights be from walls?

Start with about half the light-to-light spacing. In an 8 ft ceiling example, place the center of the nearest light approximately 2 ft from the wall. For a first sketch, 24–36 in (2–3 ft) from wall to light center is a range to test—not a required standard.

How many recessed lights do I need per square foot?

There is no fixed number of recessed lights per square foot that fits every room. This calculator starts with room area × target foot-candles ÷ (fixture lumens × 0.55 utilization × 0.8 light loss), then rounds up. Auto may increase that starting count so a complete grid also meets the calculator’s spacing limit. Use the calculation method to understand the estimate, then enter the actual room use and complete-fixture output instead of relying on a universal lights-per-square-foot ratio.