Calculate Room Lighting
Use the responsive input grid below. It shows three columns on large screens, two on medium, and one on mobile.
Formula Used
This calculator sizes lighting using room area, target illuminance, and fixture performance adjustments. It distinguishes between delivered lumens in the room and installed lumens from fixtures.
Area = Length × Width
Target Delivered Lumens = Area × Target Lux
Required Installed Lumens = Target Delivered Lumens ÷ (Utilization Factor × Maintenance Factor)
Fixtures = Ceiling(Required Installed Lumens ÷ Lumens Per Fixture)
Achieved Lux = (Fixtures × Lumens Per Fixture × Utilization Factor × Maintenance Factor) ÷ Area
Monthly Energy = (Total Wattage ÷ 1000) × Daily Hours × Days Per Month
Monthly Cost = Monthly Energy × Electricity Rate
Utilization factor reflects how well fixture light reaches the working plane. Maintenance factor allows for lumen loss from dust, aging, and dirt over time.
How to Use This Calculator
- Enter a room name and choose the room type.
- Input room length and width in meters.
- Set the target lux based on the activity.
- Enter fixture lumens and wattage from product specifications.
- Choose reasonable utilization and maintenance factors.
- Add expected daily usage and electricity rate.
- Press calculate to view fixture count, lux level, power, cost, and graph.
- Use the CSV and PDF buttons to save the result.
Example Data Table
This sample table helps compare common room types and starting illuminance targets.
| Room Type | Example Size (m) | Area (m²) | Suggested Lux | Fixture Lumens | Estimated Fixtures |
|---|---|---|---|---|---|
| Living Room | 5 × 4 | 20 | 200 | 1600 | 4 |
| Bedroom | 4 × 3.5 | 14 | 150 | 1200 | 3 |
| Kitchen | 4 × 3 | 12 | 300 | 1600 | 4 |
| Bathroom | 3 × 2.5 | 7.5 | 250 | 1000 | 3 |
| Study | 3.5 × 3 | 10.5 | 400 | 1600 | 4 |
Frequently Asked Questions
1. What is lux in room lighting?
Lux measures illuminance on a surface. One lux equals one lumen spread across one square meter. Higher lux means a brighter room.
2. Why does the calculator use utilization factor?
Not every lumen from a fixture reaches the useful area. Utilization factor accounts for fixture design, mounting, room shape, and reflection losses.
3. Why is maintenance factor important?
Lamps and luminaires lose performance over time. Dust, aging, and dirt reduce output, so maintenance factor keeps your design realistic.
4. What lux level should I choose?
Bedrooms often use 100 to 150 lux. Living rooms use about 150 to 300 lux. Kitchens and study areas usually need stronger lighting.
5. Does this calculator work for LED fixtures?
Yes. It works well for LEDs because you can enter actual fixture lumens and wattage from the product label or datasheet.
6. Why can achieved lux be higher than target lux?
Fixture count is rounded up to a whole number. That keeps the design practical, but it can make the final lux slightly higher than the minimum target.
7. Can I use feet instead of meters?
This version expects meters. If you measure in feet, convert first or adjust the code to add a unit switch.
8. Is this enough for detailed lighting design?
It is excellent for planning and quick checks. Full professional design may also consider glare, color temperature, beam spread, spacing, and surface reflectance.