[9.4.9] (Formerly called maintenance factor, MF.) The ratio of illuminance (or exitance or luminance) for a given area to the value that would occur if lamps operated at their (initial) rated lumens and if no system variation or depreciation had occurred. Components of this factor may be either initial or maintained.

Note: The light loss factor is used in lighting calculations as an allowance for lamp(s) or luminaire(s) operating at other than rated conditions (initial) and for the depreciation of lamps, light control elements, and room surfaces to values below the initial or design conditions, so that a minimum desired level of illuminance may be maintained in service. Light loss factors address losses that result in direct changes to lamp lumens, emitted luminaire lumens, or the interreflected light delivered to the space.

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