Lighting Layout Calculator

Find how many fixtures you need, how far apart to space them, and whether your circuit can handle the load — using the Zonal Cavity Method.

Room Dimensions

Length (ft)

Width (ft)

Ceiling Height

Room Type & Light Level

Room Type

Target Light Level (foot-candles)

Recommended: Living Room 20 fc

Fixture Type

Fixture Lumens

Auto-filled by fixture type. Edit to override.

Fixtures Needed

—

Enter room dimensions above

—

Total Lumens

—

Foot-candles Achieved

—

Spacing (ft)

—

Total Watts

—

Circuit Size

—

Energy Cost/yr

Lumen Method —

Spacing Method —

Final (larger) —

Assumes 80% light loss factor (LLF) for dust & lamp depreciation.

Room Layout Grid

Top-down view of your room with recommended fixture positions. Fixtures are evenly spaced with the first row offset by half the spacing from each wall.

Fixture position

Spacing dimension

Fixture Type Comparison

Fixture count and estimated cost comparison for all 4 fixture types at the same target light level in your room.

Fixture Type	Lumens	Watts	Fixtures Needed	Total Watts	Est. Unit Cost	Best For

NEC Code Reference

NEC 210.70 — Required Lighting Outlets

Location	Requirement
Habitable Rooms	At least 1 wall switch-controlled outlet
Hallways, Stairways	At least 1 wall switch-controlled outlet
Bathrooms	At least 1 wall switch-controlled outlet
Garages (attached)	At least 1 switch-controlled outlet
Outdoors (grade level)	At least 1 outlet at each entrance/exit
Attics, Crawl Spaces	At least 1 outlet at access point if used for equipment
Basements (unfinished)	At least 1 outlet

NEC 210.12 — AFCI Requirements

Location	AFCI Required?
Bedrooms	Yes (since 1999)
Family / Living Rooms	Yes (since 2014)
Dining Rooms	Yes (since 2014)
Kitchens	Yes (since 2017)
Hallways / Closets	Yes (since 2017)
Garages	Check local code
Bathrooms	Check local code
Unfinished Basement	No (typically)

Circuit Load Limits (NEC 210.19)

Breaker	80% Continuous Load	Max Lighting Watts
15A / 120V	1,440W	1,440W
20A / 120V	1,920W	1,920W
15A / 240V	2,880W	2,880W
20A / 240V	3,840W	3,840W

NEC 210.19(A)(1): Lighting circuits must not exceed 80% of breaker rating for continuous loads (3+ hours).

Recommended Light Levels by Room

Room / Task	Foot-candles (fc)
Living Room — General	10–20
Living Room — Reading	30–50
Kitchen — General	30–50
Kitchen — Counter / Task	70–100
Bedroom — General	10–20
Bedroom — Reading	30–50
Bathroom — General	50–70
Office — Desk Work	50–75
Workshop / Garage	50–100
Hallways	5–10

How This Calculator Works

Enter room dimensions — length, width, and ceiling height determine the room cavity ratio used in the Zonal Cavity Method.

Select room type — automatically sets the recommended foot-candle target. You can override this with a custom value.

Choose your fixture — the calculator uses typical lumens per fixture type and lets you override for your specific product.

Read the results — the calculator uses both the Lumen Method and Spacing Method and returns the larger fixture count as a conservative recommendation.

Check the circuit — total wattage is compared to NEC 210.19 limits to recommend a 15A or 20A breaker.

Key Terms

Lux — The SI unit of illuminance (lumens per square meter). 1 lux = 1 lumen per square foot × 10.764. Office work typically requires 300–500 lux; detailed tasks up to 1,000 lux.

Foot-candle (fc) — The imperial unit of illuminance (lumens per square foot). One foot-candle = 10.764 lux. Common targets: living rooms 10–20 fc, kitchens 30–70 fc, workshops 50–100 fc.

Lumens per Watt (efficacy) — A measure of how efficiently a light source converts electrical power into visible light. LED fixtures: 80–150 lm/W. Incandescent: 10–15 lm/W. Higher = more efficient.

Color Temperature (K) — Measured in Kelvin. 2700–3000K is warm white (residential), 4000K is neutral/cool white (offices, kitchens), 5000–6500K is daylight (workshops, task areas).

CRI (Color Rendering Index) — A scale from 0–100 measuring how accurately a light source renders colors compared to natural sunlight. CRI ≥ 90 is excellent; ≥ 80 is acceptable for most spaces.

Spacing-to-Mounting-Height Ratio — The maximum recommended horizontal spacing between fixtures divided by their mounting height above the work plane. Typically 1.0–1.5 for recessed fixtures. Exceeding this ratio creates dark spots between fixtures.

Frequently Asked Questions

What is a foot-candle?

A foot-candle (fc) is a unit of illuminance — it measures how much light falls on a surface. One foot-candle equals one lumen per square foot. It is measured at the work plane (desk height, ~2.5 ft off the floor for most rooms).

What is the Coefficient of Utilization (CU)?

CU accounts for light lost to reflections on walls, ceiling, and floor. Rooms with higher room cavity ratios (long narrow rooms, high ceilings) have more light absorbed before it reaches the work plane, resulting in lower CU values (0.45–0.55 typical).

Why does the calculator use two methods?

The Lumen Method calculates how many fixtures are needed to achieve the target foot-candles. The Spacing Method ensures fixtures are close enough together to avoid dark spots (max spacing = 1.5x mounting height). The final count is the larger of the two results to meet both criteria.

What is the Light Loss Factor (LLF)?

LLF (0.80) accounts for real-world losses: dust accumulation on lenses, lamp depreciation over time, and dirt on room surfaces. Designing to 80% efficiency ensures the light level stays above the minimum even as fixtures age.

Do bedrooms require AFCI breakers?

Yes. NEC 210.12 has required Arc Fault Circuit Interrupter (AFCI) protection for bedroom circuits since 1999. The requirement has expanded over subsequent NEC editions to cover living rooms, kitchens, and hallways. Always check your local adopted code version.