Luminaire Dirt Depreciation (LDD) is a factor that takes into account the decrease in light output due to dirt, dust and the build-up of contaminants in or on a luminaire.
As a fixture remains in use for longer periods, the amount of light effectively emitted decreases , resulting in lower illumination levels and less efficiency .
1. How is LDD calculated?
The LDD value is expressed as a ratio factor between 0 and 1 , where:
- 1.0 = No light loss (perfectly clean fixture, practically unattainable).
- 0.95 - 0.85 = Slightly polluted luminaires in clean environments such as offices.
- 0.80 - 0.50 = Moderate to heavy contamination in industrial or outdoor environments.
- 0.50 or lower = Extremely dirty fixtures (such as in factories or tunnels without maintenance).
📌 The lower the LDD, the more light loss due to pollution.
2. Factors that influence LDD
| Factor | Influence on LDD |
|---|---|
| 🏭 Environmental factors | Dust, smoke and fumes in industrial spaces accelerate pollution. |
| 🚗 Outdoor locations | Rain, mud and insects can reduce light transmission. |
| 🏢 Indoor locations | Office buildings have less dust accumulation than factories or parking garages. |
| 🏗 Luminaire design | Closed luminaires (IP65+) stay clean longer than open luminaires. |
| 🔧 Maintenance frequency | Regular cleaning reduces LDD and improves efficiency. |
📌 LDD is highly dependent on location, fixture type, and level of maintenance.
3. How is LDD applied in lighting?
✅ In lighting calculations → Included in the Light Loss Factor (LLF) .
✅ For public and industrial lighting → To compensate for light loss due to pollution.
✅ In office and shop lighting → Prevents light levels from becoming too low over time.
✅ For street lighting and tunnels → Essential to maintain safety standards.
📌 Lighting designers and engineers take LDD into account when planning lighting systems, especially in polluted environments.
4. How can LDD be reduced?
🔹 Use closed or IP-certified luminaires → Prevents the accumulation of dust and dirt.
🔹 Schedule regular maintenance and cleaning → Reduces LDD and extends the life of fixtures.
🔹 Place luminaires in strategic locations → Minimize exposure to dust and contamination.
🔹 Use self-cleaning or sealed luminaires → For example, luminaires with smooth surfaces or cover glass.
🔹 Use energy-efficient LED lighting → LEDs emit less heat, which attracts less dust.
📌 Proper maintenance and the right choice of fixtures can drastically reduce the effect of LDD.
💡 In short:
Luminaire Dirt Depreciation (LDD) is a factor that reflects light loss due to soiling of fixtures . The more dust, dirt, and contamination , the lower the LDD value , resulting in less effective lighting . Regular maintenance and smart fixture selection can minimize this effect, allowing lighting to continue operating more efficiently.