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Example data table
Use these as starting points, then confirm with drawings and requirements.
| Space type | Target illuminance (lux) | Typical UF | Typical LLF | Notes |
|---|---|---|---|---|
| Open office | 300–500 | 0.55–0.70 | 0.75–0.85 | Balanced task lighting and glare control. |
| Warehouse aisle | 100–200 | 0.45–0.60 | 0.70–0.80 | Higher mounting heights reduce UF. |
| Classroom | 300–500 | 0.55–0.75 | 0.75–0.90 | Uniformity matters for reading comfort. |
| Corridor | 100–150 | 0.50–0.70 | 0.75–0.90 | Occupancy sensors often lower diversity. |
| Parking garage | 50–100 | 0.40–0.60 | 0.65–0.80 | Consider daylight zones and switching. |
Formula used
- Required lumens: Lumens = (E × A) ÷ (UF × LLF)
- Fixture count: Fixtures = ceil(Lumens ÷ lumens per fixture)
- Connected load: W = Fixtures × watts per fixture
- Demand load: Wdemand = W × diversity factor
- Design load: Wdesign = Wdemand × (1 + spare)
- Apparent power: VA = Wdesign ÷ power factor
- Current: Single-phase: I = VA ÷ V and Three-phase: I = VA ÷ (√3 × V)
UF and LLF are planning factors. For formal design, use photometric files and validated lighting calculations.
How to use this calculator
- Enter the space area and your target lux level.
- Set UF and LLF to reflect room and maintenance conditions.
- Provide fixture lumens and watts from product data.
- Adjust diversity and spare capacity for realistic planning.
- Submit to view load, current, and breaker guidance above.
- Download CSV or PDF for records and project notes.
Lighting design inputs and what they represent
Target illuminance (lux) expresses how much light reaches the working plane. Area is converted to square meters to keep the lumen method consistent. Utilization factor approximates how efficiently fixtures deliver light to the task zone. Light loss factor covers aging, dirt, and maintenance cycles.
Fixture performance and connected load planning
Lumens per fixture should come from the product’s delivered output at the intended color temperature and optics. Watts per fixture should reflect real driver input power. The calculator multiplies fixture count by watts to estimate connected load, then reports power density in W/m² to support quick comparisons across spaces.
Demand adjustment for realistic operation
Not every circuit operates at full output all day. Diversity factor reduces connected load to an expected operating demand, which is useful for tenant fit-outs, corridors, and sensor-controlled zones. Spare capacity adds headroom for future changes, retrofit uncertainty, and minor scope growth without rebuilding the distribution plan.
Electrical quantities used for circuit sizing
Real power (kW) describes consumed power, while apparent power (kVA) accounts for power factor. Lower power factor increases current for the same watts. The calculator estimates current using single-phase or three-phase relationships and suggests a breaker size using a conservative continuous-load allowance. Final selection must match cable rating and local requirements.
Using outputs for documentation and review
The results panel summarizes lumens, fixture count, watts, kW, kVA, and current in one view. Exporting CSV supports cost models and schedules, while the PDF provides a compact record for approvals. Treat these outputs as early-stage engineering values; confirm with photometric calculations, layouts, and commissioning measurements.
FAQs
1) What if my room has mixed fixture types?
Run separate scenarios for each fixture type, then combine connected loads and demand factors. Use a weighted average only when the distribution is truly uniform and the optics are similar.
2) How do I choose utilization factor?
Use manufacturer photometric guidance when available. Otherwise start with 0.55–0.70 for typical interiors and adjust down for high mounting, dark finishes, or tight beam optics.
3) Is light loss factor the same as maintenance factor?
They are closely related. In practice, LLF often combines lamp lumen depreciation, dirt depreciation, and maintenance assumptions into a single planning value.
4) Why does power factor change current?
Lower power factor increases apparent power for the same watts, which raises current. That can affect conductor sizing, breaker selection, and voltage drop over longer runs.
5) Should I always add spare capacity?
Spare capacity is common in early design to reduce rework later. In tightly budgeted refurbishments, you may set it to zero but expect less flexibility for changes.
6) Does the breaker suggestion guarantee compliance?
No. It is a planning estimate based on calculated current and a conservative allowance. Always verify local code, derating, short-circuit levels, and equipment coordination before installation.