How many foot-candles does each room need?

IES guidelines recommend: bedrooms 10–20 fc, living rooms 10–30 fc, kitchens 30–50 fc, offices and task areas 50–70 fc, and reading areas 70+ fc.

How do I find the lumens for my light bulb?

Check the package or product label. A standard 60W-equivalent LED outputs about 800 lumens, 100W-equivalent about 1600 lumens. Always use the fixture's rated lumens, not wattage.

What spacing works best for recessed lights?

A common rule: space recessed lights at a distance equal to half the ceiling height, then double that from walls. For 8 ft ceilings, space lights about 4 ft apart and 2 ft from walls.

💡Lighting Calculator

Enter room area and lumens per fixture to find how many lights you need and how far apart to space them.

Room Area (sq ft)

sq ft

Target Illuminance

Custom Target (foot-candles)

Lumens per Fixture (lm)

How to Calculate Lighting for a Room

The standard formula is: Fixtures = (Target fc × Room sq ft × 10.76) ÷ (Lumens/fixture × Utilization Factor × Maintenance Factor). This calculator applies a utilization factor of 0.6 and maintenance factor of 0.8, which are common values for typical residential rooms with light-colored walls.

IES (Illuminating Engineering Society) recommends 10–30 fc for living and sleeping areas, and 30–70 fc for task areas like kitchens and offices. The recommended spacing is calculated as the square root of area divided by fixture count — the spacing for a uniform grid layout.

Frequently Asked Questions

What's the difference between lumens and foot-candles?

Lumens measure the total light output of a fixture. Foot-candles (fc) measure how much of that light actually reaches the work surface. 1 fc = 1 lumen per square foot. Room size, ceiling height, and reflectance affect the conversion.

Why does my room feel dark even with "enough" fixtures?

Dark walls, ceilings, and floors absorb light instead of reflecting it. Low reflectance rooms may need 20–30% more fixtures than this calculator suggests. Also, downlights create pools of light — for even coverage, surface-mounted or indirect fixtures work better.

Can I use this for recessed can lights?

Yes. Enter the lumens output of each can light (usually 650–1000 lm for a standard 4–6 in downlight), set your target illuminance, and the calculator tells you how many cans you need and the ideal spacing.

How to Calculate Lighting for a Room

Frequently Asked Questions

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