The least influence on the maintenance factor, by comparison, is exerted by the room maintenance factor which describes the reduction in reflectance values for ceiling, walls and floor and thus the reduction in utilance. Utilance is a factor for determining the utilization factor:
Room Maintenance Factor
with
UF = utilization factor
U = utilance
LOR = luminaire light output ratio.
After three years, the reduction in reflectance values slows down noticeably and the reflectance values of very clean and clean rooms increasingly turn into a constant value. For medium and highly soiled rooms, this generally does not apply. The room maintenance factor is dependent on the luminaire’s illuminance distribution (direct, direct-indirect or entirely indirect) and marginally also on room size. The following tables (a) to (i) contain the room maintenance factors according to CIE 97.2 amended by values for very clean rooms according to experience as well as measured values which are extrapolated for maintenance intervals of up to 6 years.
(a) Direct-distribution luminaires, small room, room index k ≤ 0,8
(b) Direct-indirect-distribution luminaires, small room, room index k ≤ 0,8
(c) Indirect-distribution luminaires, small room, room index k ≤ 0,8
(d) Direct-distribution luminaires, medium-sized room, room index k = 1,5
(e) Direct-indirect-distribution luminaires, medium-sized room, room index k = 1,5
(f) Indirect-distribution luminaires, medium-sized room, room index k = 1,5
(g) Direct-distribution luminaires, large room, room index k ≥ 2,5
(h) Direct-indirect-distribution luminaires, large room, room index k ≥ 2,5
(i) Indirect-distribution luminaires, large room, room index k ≥ 2,5
Table 3.29: Room maintenance factors according to CIE 97.2