What is lumen depreciation in LED streetlights?
Lumen depreciation in LED streetlights refers to the phenomenon where the luminous flux (brightness) of a luminaire gradually decreases over time during use. This is caused by factors such as defects in the LED chip material, aging of the phosphor, yellowing of the encapsulating silicone, and thermal stress. While lumen depreciation is inevitable, the rate at which it occurs can vary.
High-quality LED streetlights should exhibit less than 5% lumen depreciation over 3,000 hours of operation, and no more than 30% depreciation over 50,000 hours (a standard known as L70). In contrast, inferior products may lose more than 20% of their brightness within just 3,000 hours, leading to insufficient road illumination and creating potential safety hazards. The primary causes of lumen depreciation include:
1. Excessive junction temperature: Poor heat dissipation causes the temperature of the LED chip to rise, accelerating the aging process.
2. Excessive drive current: Operating the LED beyond its rated current accelerates chip degradation.
3. Issues with encapsulation materials: Low-quality phosphors or silicone are prone to aging and yellowing.
4. Environmental factors: Exposure to moisture or corrosive chemical gases. To mitigate lumen depreciation, it is essential to select luminaires with superior thermal management designs and ensure that the drive current remains within the specifications of the LED components. Road management authorities should conduct periodic (e.g., annual) measurements of road illuminance; if the average illuminance drops below 70% of the original design value, the replacement of the luminaires or a comprehensive system upgrade should be considered.
In procurement contracts, it is advisable to require manufacturers to provide a guarantee regarding lumen depreciation (for example, specifying that lumen depreciation shall not exceed 10% over a 5-year period).
