Building Lighting Calculator

Inputs

Formula used

This calculator uses the lumen method: Required Lumens = (Target Lux × Area) ÷ (UF × MF).

• Area is the floor area in square meters.
• UF (utilization factor) captures how effectively lumens reach the workplane.
• MF (maintenance factor) accounts for light loss over time.
• Fixtures are rounded up to meet the target lux.
• Energy: kWh/year = (Total W ÷ 1000) × hours/day × days/year.

How to use this calculator

1. Select units and enter room dimensions and ceiling height.
2. Set a target lux level suited to your activity.
3. Enter UF and MF, or keep the suggested defaults.
4. Provide lamp lumens, lamps per fixture, and fixture power.
5. Add operating hours, days, and tariff for cost estimation.
6. Press Calculate to see results above the form.
7. Use CSV/PDF buttons to export the current result.

Example data table

Examples are illustrative; actual designs depend on photometric files and surfaces.

Building lighting planning article

1) Why illuminance matters for everyday spaces

Good lighting improves comfort, safety, and productivity. Illumination is measured in lux, which is lumens falling on one square meter of a task surface. Under-lighted rooms can cause eye strain and mistakes, while over-lighting can increase glare and energy use.

2) Choosing a practical target lux level

Typical planning targets are 100–200 lux for corridors, 200–300 lux for general living areas, 300–500 lux for offices and kitchens, and 500–750 lux for detailed tasks. Use higher lux where reading, inspection, or precise work occurs, and lower lux for circulation areas.

3) The lumen method used by this calculator

The calculator estimates total luminous flux using: Required Lumens = (Target Lux × Area) ÷ (UF × MF). Area is the floor area, then UF and MF adjust for how much light reaches the workplane over time. The fixture count is rounded up so the design meets or slightly exceeds the target.

4) Understanding utilization factor (UF)

UF depends on room geometry and surface reflectance. Light-colored ceilings and walls usually increase UF because they bounce more light back into the room. For early estimates, UF often falls between 0.45 and 0.75. Deeper rooms, dark finishes, and indirect optics tend to reduce UF.

5) Maintenance factor (MF) and real-world light loss

MF accounts for lamp lumen depreciation and dirt on luminaires and surfaces. In cleaner environments with routine maintenance, MF might be 0.80–0.90. In dusty areas or where cleaning is infrequent, MF may drop to 0.70 or lower, increasing required lumens to maintain the same lux.

6) From lumens to fixtures and wattage

Fixtures combine one or more lamps, so lumens per fixture equals lamp lumens multiplied by lamps per fixture. Pair the output with realistic power (watts) to estimate energy. Modern LED fixtures commonly deliver strong light output at lower watts than older technologies, reducing annual kWh.

7) Spacing guidance for uniformity

Even distribution matters as much as total lux. A common rule-of-thumb uses a spacing criterion (often 1.0–1.5) times the mounting height above the workplane to suggest maximum spacing. If the proposed grid spacing exceeds that limit, you may see darker patches and uneven lighting.

8) Energy, cost, and smarter operating patterns

Annual energy is estimated from total watts, hours per day, and operating days per year. Reducing run time through occupancy sensors, daylight dimming near windows, and zoned switching typically saves more than minor lumen reductions. Use the tariff field to translate kWh into a budget-friendly yearly cost estimate.

FAQs

1) What is the difference between lux and lumens?

Lumens describe total light output from a source. Lux describes how much of that light reaches a surface: lumens per square meter. Lux changes with distance, layout, and room reflectance.

2) How do I pick UF and MF if I am unsure?

For early planning, try UF = 0.55–0.65 for typical rooms and MF = 0.75–0.85 for reasonably clean spaces with periodic maintenance. Then compare results with fixture photometric data later.

3) Why does the calculator recommend rounding up fixtures?

Real installations have variations from reflectance, aging, and aiming. Rounding up helps ensure the target lux is met after losses, rather than delivering a design that is marginal or dim.

4) Does higher lux always mean better lighting?

No. Excessive lux can increase glare and discomfort, especially with bright bare sources. Balanced design uses appropriate lux, good diffusion, correct color temperature, and controlled brightness to suit the task.

5) Can I use this for outdoor lighting?

It is intended for interior planning. Outdoor lighting depends strongly on beam distribution, mounting, and environmental conditions. Use dedicated outdoor lighting design methods and local standards for safety areas.

6) Why does spacing matter if total lux meets the target?

Total lux can be adequate while the room still looks patchy. Poor spacing creates bright spots under fixtures and darker zones between them. Uniformity improves comfort and perceived brightness.

7) How accurate is the energy and cost estimate?

It is a planning estimate based on entered wattage and operating schedule. Actual use varies with controls, dimming, and occupancy. Use your metered tariff and realistic hours to get closer results.