The purpose of the maintenance factor is to take into account the light depreciation
According to the new standard, designers now have a greater planning responsibility for the installation. One aspect, the maintenance factor, has a direct effect on the installations energy consumption.
In order to enable the choice of a high maintenance factor, careful consideration must be exercised when choosing light sources, luminaires and overall lighting systems.
Regardless of the type of light source, the luminous flux will always decrease over time. The degradation of luminous flux is reported as an L-value for each type of LED luminaire. L90 at 50,000 h means that the luminaire generates 90% of its original output after 50,000 h. In a light calculation, the function of the maintenance factor is to make adjustments for the installation’s light depreciation over time. In other words, the maintenance factor ensures that the lighting system fulfils lighting requirements across its stated operational life, taking into account both light depreciation and contamination with dirt.
The maintenance factor forms the foundation for establishing the maintenance plan for the lighting system.
Table 1. Proportion of the maintenance factor formed by the light source's light depreciation
| Examples of light sources | Light depreciation factor |
|---|---|
| Straight fluorescent lamps with barrier layer for low light depreciation and high pressure sodium lamps | 0.90 |
| Other fluorescent lamps, compact fluorescent lamps and mercury lamps | 0.85 |
| Metal halide lamps | 0.75 |
| LEDs | Depending on the L-value |
Table 3. Proportion of the maintenance factor corresponding to the contamination of the luminaire, taking into account the luminaire type, surroundings and cleaning interval
| Number of years between group cleanings | 2.0 | 3.0 | 4.0 | 5.0 | ||||
|---|---|---|---|---|---|---|---|---|
| Luminaire type | Surroundings | Surroundings | Surroundings | Surroundings | ||||
| Clean | Dirty | Clean | Dirty | Clean | Dirty | Clean | Dirty | |
| Open luminaire | 0.96 | 0.85 | 0.94 | 0.77 | 0.92 | 0.72 | 0.9 | 0.66 |
| Closed luminaire | 0.98 | 0.87 | 0.96 | 0.84 | 0.94 | 0.78 | 0.92 | 0.71 |
| Indirect uplight luminaire | 0.91 | 0.68 | 0.84 | 0.54 | 0.77 | 0.40 | 0.71 | 0.29 |
| Table 3 is an adaptation of CIE 97:2005 2nd Edition. Open luminaire refers to both direct and direct/indirect distribution, while uplight luminaire is 100% indirect. |
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Table 4. Proportion of the maintenance factor corresponding to the contamination of the surfaces in the room, taking into account the luminaire type, surroundings and cleaning interval. A 3 year interval is recommended for comparison.
| Number of years between group cleanings | 2.0 | 3.0 | 4.0 | 5.0 | ||||
|---|---|---|---|---|---|---|---|---|
| Luminaire type | Surroundings | Surroundings | Surroundings | Surroundings | ||||
| Clean | Dirty | Clean | Dirty | Clean | Dirty | Clean | Dirty | |
| Direct | 0.97 | 0.95 | 0.97 | 0.95 | 0.97 | 0.95 | 0.97 | 0.95 |
| Direct/Indirect 50/50 | 0.95 | 0.90 | 0.95 | 0.90 | 0.95 | 0.90 | 0.95 | 0.90 |
| Indirect | 0.92 | 0.77 | 0.92 | 0.77 | 0.92 | 0.77 | 0.92 | 0.77 |
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Reflection factors 70/50/20 and 50/30/20 dirty. Tables 1, 3 and 4 must be used together to calculate a maintenance factor. |
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| Standard formula for maintenance factor = LLMF x LSF x LMF x RSMF (Lamp Lumen Maintenance Factor x Lamp Survival Factor x Luminaire Maintenance Factor x Room Surface Maintenance Factor = maintenance factor) (see explanation under Quantities, units and their significance). | ||||||||
For example:
LED luminaire with L90, open luminaire in clean surroundings, 3-year cleaning interval and direct-indirect luminaire, exchange immediately in the event of failure
0.9x1x0.94x0.95 = 0.8
Selecting a luminaire with L90 is an advantage.- The L-value after a specified number of burning hours affects the maintenance factor.
- A higher L-value gives a higher maintenance factor.
- Luminaires with higher maintenance factor meet the operating values with fewer luminaires, which can positively impact on energy consumption.
For example:
Classroom with L80 or L90 luminaires.
Calculation of maintenance factor with pendant luminaires in a clean environment with 3-year cleaning interval.
Values for lamp survival factor, luminaire contamination and room contamination are reported in the Lighting template.
The difference in a light calculation:
An operating value of 445 lux is obtained for an installation with L80 luminaires, which is not sufficient to meet the standard requirement of 500 lux. For the system to comply with the requirement, 12 luminaires would have to be installed. L90 luminaires, that have a higher maintenance factor, meet the standard requirement of 500 lux with only nine luminaires. Threfore using the L90 luminaire the requirement is met with fewer luminaires.
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| Classrooms with pendant L80 luminaires |
Classrooms with pendant L90 luminaires |
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| Requirement according to EN 12464-1 | 500 lux | 500 lux |
| Maintenance factor | 0.71 | 0.8 |
| Value when new | 625 lux | 625 lux |
| Operating value Em | 445 lux (does not meet requirement) | 501 lux |