Light losses during the use of a lighting installation, caused by the decrease of the luminous flux of lamps, the dirt accumulation on and loss of reflectivity and or transparency of luminaires, and dirt accumulation on or discoloration of room surfaces (in interiors).
Lamp Lumen Depreciation
The light output of virtually all lamp types declines gradually during operation. The causes of light output depreciation are numerous. With incandescent lamps, it is especially the blackening of the bulb – caused by evaporation of the filament. Discharge lamps also suffer from blackening, in this case due to scattering of the electrode material, which settles on the wall of the discharge tube. With fluorescent lamps, high-pressure mercury lamps, and solid state, LED, and OLED light sources with a fluorescent coating, the major cause of light output depreciation is a gradual exhaustion of the fluorescent powder, which slowly loses its effectiveness.