How is the lumen depreciation of LED streetlights measured?

Measuring the lumen depreciation of LED streetlights is a key method for assessing their operational status and determining whether they need to be replaced. Such measurements can be conducted either in the field or in a laboratory setting.

Field Measurement:

1) Select representative road sections and establish fixed measurement points (typically arranged in a grid pattern with a spacing of 5–10 meters).

2) Using a Class 1 illuminance meter (with an accuracy of ±2%), measure the illuminance at each point during the night—ensuring conditions are dry, with no rain or fog—and calculate the average illuminance.

3) Compare the results against the initial design values ​​or data from previous measurements. Lumen depreciation = (Initial Illuminance - Current Illuminance) / Initial Illuminance × 100%.

4) It is recommended to conduct measurements at the same time of year and at the same time of day to minimize the influence of environmental variables.

Laboratory Measurement: This involves removing the streetlights and transporting them to a laboratory, where an integrating sphere or a goniophotometer is used to measure the absolute luminous flux, which is then compared against the manufacturer’s original specifications. While this method offers higher precision, it also entails higher costs.

Smart Monitoring: Some LED streetlights are equipped with built-in power monitoring and timing functions; by applying a lumen depreciation model, the remaining service life can be estimated. When lumen depreciation reaches 30% (the "L70" threshold), replacement of the luminaire should be considered. For major arterial roads, if the average illuminance falls below the minimum design standard, the luminaires should be replaced—even if the lumen depreciation has not yet reached 30%. All measurement records should be archived to serve as a basis for future maintenance decisions.