What is Luminaire Dirt Depreciation (LDD)
Luminaire Dirt Depreciation (LDD) describes the reduction in light output or performance of a luminaire caused by the accumulation of dirt, dust, or other contaminants on its surfaces. Over time, the buildup of dirt and debris on a luminaire can obstruct the light emitted, resulting in a decrease in the amount of light reaching the desired area.
The LDD factor is a measure of the extent to which a luminaire’s performance is affected by dirt accumulation. It is typically expressed as a percentage or a factor that represents the reduction in light output caused by dirt depreciation. The LDD factor is an important consideration in lighting design and maintenance as it helps estimate the reduction in light output over time and plan for appropriate cleaning and maintenance schedules.
To determine the LDD factor for indoor environments, a five-step procedure outlined in the IESNA/NALMCO RP-36-03, Recommended Practice for Planned Indoor Lighting Maintenance, is often followed. This procedure involves characterizing the operating environment, categorizing the luminaire, determining the CIE classification, assigning a letter based on the working environment and CIE classification, and selecting the appropriate LDD factor from a set of curves published in the document.