12464-1:2001 standard states that as far as the lighting equipment maintenance factor is concerned CIE 97:2005 (2nd edition) should be taken into consideration. It is calculated using the following formula:

MF=LLMFxLSFxLMFxRSMF

Where:

MF = maintenance factor.

LLMF = % of the physical luminous flux degradation of a lamp.

LSF = lamp survival factor expressed in %, i.e. the number of lamps still functioning after a certain period of time.

LMF = luminaire maintenance factor: % of luminous flux degradation of the luminaire over time.

RSMF = room surface maintenance factor is the % of degradation of light from reflective surfaces of a room over time.