AS NZS 1680.4:2017 Interior and workplace lighting
3.2 LAMP LUMEN MAINTENANCE FACTOR (LLMF)
The output of all lamps will progressively decrease with use. The exact rate, however, depends upon many factors, including lamp type, control gear, switching cycles, dimming, electrical supply and thermal conditions. Table B2 shows typical examples for general information. As lamps of different types and lamps of the same general type from various manufacturers may exhibit widely differing characteristics, it is very important to obtain up-to-date data from the lamp manufacturers for estimating the maintenance factor and the maintenance program, particularly when using a new type of lamp.
3.3 LAMP SURVIVAL FACTOR (LSF)
Lamp survival is the probability of lamps continuing to operate for a given time. The survival rate depends upon many factors, including lamp type, control gear, switching cycles, dimming, electrical supply, thermal conditions and vibration. Failed lamps cause reductions in the illuminance and uniformity, but the effect can be minimized by spot replacement of lamps. Table B2 shows typical values. For accurate data, the lamp manufacturer should always be consulted.
If the failure of one or more lamps compromises the maintenance illuminance required for the task(s), a maintenance plan should be in place that ensures the failed lamps are immediately replaced. Where such a spot lamp replacement program is adopted, a lamp survival factor of 1 may be assumed.
3.4 LUMINAIRE MAINTENANCE FACTOR (LMF)
Dirt on lamps and luminaires will generally cause the greatest light loss. In industrial lighting systems it is not uncommon to find 50% loss due to dirt build-up during long intervals between cleaning. The amount of light loss depends on the nature and density of airborne dirt, luminaire design, luminaire finish and lamp type. For example, areas vary as to the amount and type of dirt in the air; the amount of dirt in a foundry is greater than that found in an air conditioned office. But the amount and type of dirt in an office located near an industrial area is different from that in an office located in the country. The black dirt found in steelworks is most unlike the relatively light-coloured dust in bakeries. It is important to be able to recognize these variations when assessing light losses. Luminaire surfaces differ in their resistance to dirt accumulation and the nature of the dirt or dust involved will affect the level to which it adheres to the surface. Dust with high oil content will tend to adhere while dry dust can be blown off again. Some plastic materials and plastic paints can be statically charged and as a result actively attract dust.
The choice of luminaire type will depend on the nature of the dust involved.