The lumen method
Lighting designers size general lighting with the lumen method. You decide how bright the working surface should be (in lux), multiply by the area, and divide by the useful light each fixture delivers. Not all lumens reach the desk: some are absorbed by walls and ceiling, and output drops as fixtures age and collect dust. Two factors account for this – the utilization factor (UF) and the maintenance factor (MF).
Number of fixtures = (target lux × area m²) ÷ (lumens per fixture × UF × MF)
Utilization factor and room index
The utilization factor depends on the room's shape and how reflective its surfaces are. Wide, low rooms with white ceilings use light efficiently (UF up to 0.7); narrow, tall rooms with dark walls waste more (UF 0.3 – 0.4). The room index k = L × W ÷ (Hm × (L + W)) captures the shape, where Hm is the height of the fixtures above the desk (about 0.8 m from the floor). LuxLayout estimates UF from k and your surface colors.
Recommended light levels
| Area | Lux | Foot-candles |
|---|
| Corridors, storage | 100 – 150 | 10 – 15 |
| Reception, break room, restrooms | 200 – 300 | 20 – 30 |
| Offices, writing, typing, computer work | 500 | 50 |
| Meeting & conference rooms | 300 – 500 (dimmable) | 30 – 50 |
| Technical drawing, detailed tasks | 750 | 75 |
These values follow EN 12464-1 and IES recommendations for maintained illuminance on the work plane. One foot-candle equals about 10.76 lux.
Choosing LED fixtures
- Efficacy: look for 110 – 140 lumens per watt; older fluorescent troffers manage 60 – 80.
- Glare: UGR below 19 for computer workplaces; avoid bare high-output LEDs above desks.
- Color temperature: 3,500 – 4,000 K neutral white is standard for offices; 3,000 K for lounge areas.
- Color rendering: CRI 80 minimum, CRI 90 for design and retail spaces.
- Flicker: choose drivers with low flicker (IEEE 1789 compliant).
- Controls: 0 – 10 V or DALI dimming, occupancy sensors and daylight harvesting.
Layout and spacing
Arrange fixtures in a regular grid with half spacing between the outer row and the wall. To keep light even, spacing should not exceed about 1.2 – 1.5 times the mounting height above the work plane. In open offices align rows with desks; in meeting rooms add a dimmable separate circuit so the screen remains readable.
Energy and payback
Replacing a 4-lamp T8 troffer (about 110 W) with a 36 – 40 W LED panel saves roughly 70 W per fixture. At 2,600 hours a year and $0.17/kWh that is about $30 per fixture annually – so LED retrofits often pay back in two to four years, faster with utility rebates.
Frequently asked questions
How many lux are needed in an office?
About 500 lux on the desk for computer and paper work, 300 lux in break areas and 100 – 150 lux in corridors.
How many LED panels for a 10×10 m office?
With 4,000 lm panels, light surfaces and 500 lux, roughly 20 – 25 panels arranged in a 5 × 5 grid.
What is a good lighting power density for offices?
Modern LED offices typically use 5 – 8 W/m² (0.5 – 0.75 W/ft²), within most energy code limits.
What color temperature is best for offices?
Neutral white around 3,500 – 4,000 K is preferred for workspaces; warmer 3,000 K suits lounges and break areas.
What is the maintenance factor?
It accounts for light loss over time from LED aging and dirt. 0.8 is typical for clean offices with modern LEDs.
About LuxLayout
LuxLayout is an independent, free calculator for planning LED lighting in offices, meeting rooms and workshops using the lumen method and IES / EN 12464-1 recommendations. We are not a lighting manufacturer or distributor. For code compliance consult a lighting designer.
Every formula on this page runs entirely in your web browser. The numbers you type are never uploaded, stored or shared. Our goal is simple: give you an honest starting point so you can compare product specifications with confidence and avoid paying for capacity you do not need – or buying something too small to do the job.
The methodology combines widely published engineering rules of thumb, manufacturer data sheets and the electrical code practices that installers use every day. We review the assumptions regularly and update the calculator when typical product specifications change.
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Last updated: October 28, 2026
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