KEY TAKEAWAYS
- Calculate maintained rather than initial illuminance
- Account for lumen depreciation and dirt
- Use assumptions that match the real environment
- Coordinate access and cleaning intervals
- Avoid energy waste from unnecessary overlighting
01Why Maintained Illuminance Matters
Lighting calculations should predict the illuminance available near the end of a maintenance period, not only the value on the first day.
Dust, aging and surface changes reduce delivered light over time.
02The Main Components
Maintenance factor typically considers lamp or LED lumen maintenance, luminaire dirt depreciation, room surface dirt and maintenance practices.
The appropriate approach depends on the calculation standard and project conditions.
Practical Design Checklist
01 The Main Components
Maintenance factor typically considers lamp or LED lumen maintenance, luminaire dirt depreciation, room surface dirt and maintenance practices.
02 Environment Changes the Result
A clean hotel lobby and a dusty industrial space should not use the same assumption. Ceiling height, ventilation, pollution, cleaning access and surface reflectance all influence long-term performance.
03 Maintenance Interval and Access
Shorter cleaning intervals can support a higher maintenance factor, while inaccessible high ceilings may require more conservative assumptions.
04 Avoid Overlighting
Using unrealistic maintenance assumptions can cause underlighting later; compensating blindly with excessive initial light wastes energy and increases glare.
03Environment Changes the Result
A clean hotel lobby and a dusty industrial space should not use the same assumption. Ceiling height, ventilation, pollution, cleaning access and surface reflectance all influence long-term performance.
Document the environmental category used in the calculation.
04Maintenance Interval and Access
Shorter cleaning intervals can support a higher maintenance factor, while inaccessible high ceilings may require more conservative assumptions.
Coordinate the lighting design with safe access, cleaning schedules and replacement strategy.
Specification Review Matrix
| Design Question | What to Verify | Why It Matters |
|---|---|---|
| Performance | Calculate maintained rather than initial illuminance | Use assumptions that match the real environment |
| Application | Account for lumen depreciation and dirt | Coordinate access and cleaning intervals |
| Maintenance | Use assumptions that match the real environment | Avoid energy waste from unnecessary overlighting |
05Avoid Overlighting
Using unrealistic maintenance assumptions can cause underlighting later; compensating blindly with excessive initial light wastes energy and increases glare.
Select efficient optics, realistic factors and a documented maintenance plan to meet the target throughout the project life.