Field Study of Luminaire Dirt Depreciation

A field study of luminaire dirt depreciation was conducted over a three year period and included over 200 sites in the U.S. Recessed 2 x 2 and 2 x 4 fluorescent luminaires, both louver and lens-panel types, were incorporated in the study. The sites included offices, schools and retail establishments. The IESNA recommended luminaire dirt depreciation factors now in use were formulated in the middle of the last century. Analysis of the results from this present study shows these existing recommendations significantly overestimate the light loss due to dirt deposited on luminaire surfaces. The improvement found in luminaire dirt depreciation factors is believed to be principally due to changes in the indoor environment since the 1950s when the original luminaire dirt studies were made. The significance of these results is that the increase in the initial design light level over the required maintained light level is less in those applications where the results of this study are applicable.