Calculator inputs
Use room dimensions for a layout suggestion, or switch to manual area when only total floor area is known.
Example data table
| Space type | Area (m²) | Target lux | Fixture lumens | CU | LLF | Estimated fixtures |
|---|---|---|---|---|---|---|
| Site office | 60 | 300 | 3600 | 0.72 | 0.80 | 8 |
| Workshop bay | 180 | 500 | 5200 | 0.70 | 0.78 | 32 |
| Storage room | 96 | 150 | 2800 | 0.68 | 0.80 | 10 |
| Corridor zone | 45 | 100 | 2200 | 0.65 | 0.82 | 4 |
Formula used
Required Lumens = Area × Target Illuminance
Effective Lumens per Fixture = Fixture Lumens × Coefficient of Utilization × Light Loss Factor
Raw Fixture Count = Required Lumens ÷ Effective Lumens per Fixture
Adjusted Fixture Count = Raw Fixture Count × (1 + Spare Percentage ÷ 100)
Achieved Lux = (Installed Fixture Count × Effective Lumens per Fixture) ÷ Area
How to use this calculator
- Select room dimensions when you know length and width, or choose manual area if total area is already available.
- Enter the target lux required for the construction zone or room function.
- Enter the lumen output and wattage of the lighting fixture being considered.
- Set coefficient of utilization and light loss factor using your project assumptions.
- Add a spare percentage when you want extra coverage for layout rounding or planning margin.
- Enter spacing criterion and mounting height for a simple spacing review.
- Submit the form to view count, achieved lux, watts, layout suggestion, graph, and export options.
Frequently asked questions
1) What does this calculator estimate?
It estimates how many lighting fixtures are needed to reach a target illuminance across a floor area. It also reports wattage, power density, achieved lux, and a simple layout suggestion when room dimensions are provided.
2) Why are CU and LLF included?
They reduce nominal fixture lumens to a more realistic usable value. CU reflects how well lumens reach the working plane. LLF accounts for dirt, aging, and other losses over time.
3) Why is the result rounded up?
Lighting fixtures are installed as whole units. Rounding up ensures the design does not undershoot the target illuminance after applying utilization and loss adjustments.
4) What target lux should I use?
Use the value required by your project brief, client standard, or applicable design guidance. Offices, corridors, workshops, and storage areas often need very different illuminance levels.
5) What does spare percentage do?
It adds planning allowance above the raw count. Designers use it to cover layout balancing, future flexibility, or extra assurance during early construction-stage estimating.
6) Is the spacing suggestion a final layout?
No. It is an early layout guide based on room proportions and count. Final lighting design should still consider beam spread, glare, reflectance, obstructions, and detailed photometric analysis.
7) Can I use this for renovation projects?
Yes. It works for new construction and renovation planning. Just use realistic fixture data and project-specific illuminance targets for the existing or proposed space.
8) What if achieved lux is much higher than target?
That usually means the selected fixture is powerful for the chosen area, or the count has been rounded for layout reasons. You can test another fixture or revise the layout assumptions.