Recessed Lighting Calculator

The number of recessed lights depends on your room size, ceiling height, target brightness (foot-candles), and the lumens each fixture produces. A common starting point is to divide the room's square footage by the fixture spacing squared. This calculator handles all of that automatically and gives you a rows × columns grid based on your inputs.

The widely used rule of thumb is to space recessed lights roughly 0.8× your ceiling height apart. For a 9 ft ceiling, that works out to about 7.2 ft between fixtures. You can tighten the spacing (0.6×) for task areas like kitchen counters or widen it slightly (1.0–1.2×) for accent or mood lighting.

The first row is typically placed about half the fixture-to-fixture spacing distance from the wall — roughly 2–3 ft for standard rooms. This prevents a harsh bright spot near the wall and promotes even illumination across the full floor area.

The result is a first approximation using the standard lumen method formula: (fixtures × lumens × maintenance factor) ÷ room area. Real-world results vary depending on fixture beam angle, ceiling reflectance, wall colors, and obstructions. For critical applications like commercial spaces, a full photometric plan from a lighting designer is recommended.

The maintenance factor (MF) accounts for the gradual reduction in light output over time due to lumen depreciation and dust accumulation on fixtures. A common value is 0.8, meaning the system is designed to deliver 80% of its initial output at its lowest expected point. Using a higher MF like 1.0 gives optimistic results; 0.7 is more conservative.

Recommended foot-candle levels vary by use: hallways need about 8–10 fc, living rooms and bedrooms around 10–20 fc, bathrooms 30–50 fc, general kitchen lighting 30–50 fc, and kitchen task or island areas 70–100 fc. This calculator lets you pick your room type and automatically sets an appropriate target.

Glare is mainly influenced by the fixture's beam angle and its mounting depth relative to the ceiling. A wider beam angle (e.g. 90°) spreads light more evenly but can cause glare if the fixture is too exposed. Uniformity improves when spacing is consistent and the wall offset is set to roughly half the fixture spacing. Dimming capability also helps balance brightness throughout the day.

A photometric plan is worth commissioning for commercial spaces, large open-plan areas, spaces with unusual geometry or high ceilings, or any project where building codes require documented light levels. For typical residential rooms, this calculator gives a reliable starting layout that you can refine with your electrician.