Lighting Design calculator

Lighting Design Calculator

A 60 x 40 ft office at 35 fc with 4,000 lm fixtures, CU 0.78, and LLF 0.80 needs about 134,615 lumens and screens at 34 fixtures in a 5 rows x 7 columns layout. This lighting design calculator is a preliminary lumen-method screen for early U.S. project planning. It works in feet and footcandles first, then reports the metric equivalents so you can estimate total lumens, fixture count, and a basic rectangular layout without pretending to be a full photometric study or an energy-code checker.

Updated June 8, 2026

Fixture count = (target fc x area ft²) ÷ (fixture lumens x CU x LLF). A 2,400 ft² office at 35 fc with 4,000 lm fixtures, CU 0.78, and LLF 0.80 screens at 34 fixtures.

Required lumens = target fc x area ft² ÷ (CU x LLF)

Enter room size in feet, planning footcandles, CU, LLF, and optional fixture lumens to screen total lumens, fixture count, and a basic grid layout.

Calculator Inputs

Calculation Results

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Calculation history

Example Calculations

Open office planning screen

Estimate total lumens and fixture count for a 60 ft x 40 ft office.

Inputs

Room Length: 60
Room Width: 40
Ceiling Height: 10
Working Plane Height: 2.5
Space Type: Office
Utilization Factor: 0.78
Maintenance Factor: 0.8
Lamp Lumens: 4000

How to Use

What this lighting design calculator does

This page helps you answer a practical early-design question: how many lumens and fixtures do I need for this room? Enter room dimensions in feet, choose a planning footcandle target, and apply your assumed coefficient of utilization (CU) and light loss factor (LLF).

Required lumens = (target footcandles x area in ft²) ÷ (CU x LLF)

If you also enter fixture lumens, the calculator rounds up to a whole fixture count and suggests a simple rows-by-columns layout. That spacing output is only a screening aid. Final spacing still depends on the fixture photometrics, spacing criterion, glare control, surface reflectances, and the actual task area.

Common starting targets

Space	Typical starting target	Metric equivalent
Corridor	10 fc	108 lux
Open office	35 fc	377 lux
Classroom	40 fc	431 lux
Warehouse	20 fc	215 lux
Retail floor	50 fc	538 lux

These are planning targets, not permit-ready guarantees. Confirm the final criteria against the current project basis, owner requirements, fixture photometrics, and any adopted lighting or workplace rules that apply to the actual site.

How to use the inputs

Room length and width: enter the actual floor dimensions in feet.
Ceiling height and working plane: use the luminaire mounting height above the task plane, not just the slab-to-slab dimension.
Planning target: choose a common starting footcandle level or enter a custom target.
CU: use a realistic coefficient of utilization for the room proportions and fixture distribution.
LLF: include dirt, aging, and maintenance assumptions honestly.
Fixture lumens: enter delivered lumens for one fixture only if you want fixture count and spacing.

Worked example

A 60 ft x 40 ft office uses a 35 fc planning target, CU = 0.78, and LLF = 0.80.

Area = 2,400 ft²
Required lumens = 35 x 2,400 ÷ (0.78 x 0.80) = 134,615 lumens
With 4,000 lumen fixtures, the screen rounds up to 34 fixtures
The page then proposes a basic rectangular grid and reports the achieved average footcandles from that rounded count

What this page does not do

It does not estimate lighting power density from fake efficacy assumptions.
It does not replace a photometric layout, AGi32 model, or manufacturer spacing check.
It does not certify code compliance, glare control, emergency egress performance, or daylight controls.

Common Applications

Preliminary room-lighting checks for offices, classrooms, retail areas, and warehouses

Early fixture-count screening before you open a photometric file

Quick conversion between footcandles and lux for the same room target

Basic rectangular layout planning before a full lighting design pass

Frequently Asked Questions

Is this a code-compliance or energy-code calculator?

No. This page is a preliminary lumen-method screen. It helps estimate lumens and fixture count, but it does not claim lighting power density compliance, glare performance, emergency-lighting compliance, or final photometric adequacy.

Why does the calculator use footcandles first?

Because the site targets U.S. users and the lumen method is straightforward in footcandles: one footcandle is one lumen per square foot. The page still reports the metric lux equivalent so you can cross-check both systems.

What are CU and LLF?

CU is the coefficient of utilization, meaning how much of the fixture output reaches the working plane. LLF is the light loss factor, which accounts for depreciation, dirt, and maintenance assumptions. Both terms directly affect the required total lumens.

Should I trust the spacing output as a final layout?

Treat it as a screen only. The suggested spacing comes from a simple rectangular distribution of the rounded fixture count. Final layout still depends on the fixture photometric distribution, spacing criterion, room reflectances, glare limits, and task locations.