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Lighting Maintenance Factor


Degradation of the Illumination System

Illumination Systems are designed to fulfill the required lighting level at the end of an operation term and not at day one of the new installation.  
The luminous flux of the system is going down over lifetime. This is a normal process, no product is lasting forever but the required illuminance levels should not be depreciated at any time. Standards like the CIE 97:2005, help to choose the right maintenance factor in different areas. If a lighting system is setup, the maintenance plan has to be fixed too. So the facility managers know how often to clean the room, the luminaires and how frequently to change lamps. A reasonable time needs to be found between maintenance and operating hours, as maintenance cycles are connected to costs. The longer the operation time without maintenance, the more luminaires need to be installed to guarantee the required illumination level at the end of the term. The more frequent the maintenance cycles, the higher the maintenance factor, but also the related costs for the facility service.

Which points are influencing the Maintenance Factor?

The installations illumination level is going down over time. Different factors influence the decrease in lighting level like the soiling of the room surfaces, the soiling of the luminaires, depreciation of luminous flux by the light sources or lamps failure.
 
 

 
 
  Room Surface Maintenance Factor
The room surface maintenance factor is the ratio of the room surfaces reflectance before and after cleaning. It is the reduction of the lighting level according to soiling of the room. It depends highly on the conditions in a room, if the room is very clean, clean, dirty or very dirty. The more dirty the room, the lower the maintenance factor.
 
 
  Luminaire Maintenance Factor
The luminaire maintenance factor is the ration of the luminaires luminous flux before and after cleaning. It depends on the luminaire construction and design (open housing or closed one) as well as on environmental conditions (dirty or clean). The higher the luminaires protection degree from dust, and the cleaner the room, the higher the maintenance factor.
Consider the accessibility of the luminaires when setting up the maintenance plan. The more difficult to reach, the more the maintenance costs will be.
 
 
  Lamp Maintenance Factors
 
 
a) Lamp Lumen Maintenance Factor
The lamp lumen maintenance factor is the ration of luminous flux at a specific time compared to a new lamp. It is describing the aging of the lamp or the reduction of light intensity over time. Manufacturers offer comprehensive tables about their lamps luminous flux behavior.
 
b) Lamp Survival Factor
The lamp survival factor depends on the service lifetime of a lamp. Some lamp lifetimes are reduced by frequent switching. The lamp manufacturers provide tables indicating the lamp survival factor. If a lamp is not working any more, the decision for immediate replacement or group replacement needs to be taken. If the lamp is replaced immediately (mostly in areas where the luminaire is easily reachable) the LSF can be set 1. LSF 1 is saying that there will be no loss of light because of lamp failure. On the other hand, the decision could be to replace lamps in special terms or group-wise. This could be the case in huge halls, where machines need to be stopped to reach the luminaires. The stopping of the machines is connected to less production rates of the factory, so they won’t change each single lamp.
 

Calculation examples
 
Open-Plan Office (50 employees)
  • Working hours: 5 days a week, 16h each day, 50 working weeks a year (4000h/a)
  • Office renewed after 10 years (40,000h total)
  • Rooms are very clean
  • The room and its surfaces are cleaned regularly
  • Lighting System: pendant closed luminaires (IP40)
  • LED light sources

 

Maintenance Factor MF:

MF = RMF x LMF x LSF x LLMF
  very clean room closed luminaire LED is not failing LED luminous flux degradation over 40,000h
MF = 0.97 0.92 1 0.9
MF =
0.8      
 

A maintenance factor of 0.8 shows, that the new lighting system needs to be overdriven by 25% not to undercut the minimum required illumination level after 10 years.


 

Factory Hall (150m²)
  • Working hours: 7 days a week, 18h each day, 54 working weeks a year (6,800h/a)
  • Hall is going to be renewed after 15 years (102,000h total)
  • Rooms are dirty
  • The room and its surfaces are cleaned every 5 years
  • Lighting System: pendant closed luminaires (IP64)
  • LED light sources


MF = RMF x LMF x LSFx LLMF
  dirty room closed luminaire (IP65) LED is not failing LED luminous flux degradation over 100,000h
MF = 0.9 0.94 1 0.7
MF = 
0.6      


A maintenance factor of 0.6 means, the new lighting system is over-driven by 67% not to undercut the minimum required illumination level. LED lighting systems are flexible and easy to connect to control systems. The installed load will provide efficient luminous flux at the end of the operation time but the energy that is “over” in the beginning can be saved. The new installation would illuminate an area with required 300lx by about 450lx. The energy can be saved by lighting management systems that are regulating the power concerning the luminous flux depreciation.

 
Same features as above - HID light source
  • HID light sources
  • Replacement every 2 years (13,600h)

 

MF = RMF x LMF x LSF x LLMF
  dirty room closed luminaire (IP65) HID service lifetime HID luminous flux depreciation over 13,600h
MF = 0.9 0.94 0.84 0.65
MF =  0.46      


A maintenance factor of 0.46 means, the new lighting system is overdriven by over 100% not to undercut the minimum required illumination level. So the double installed power than on day one is necessary. HID lamps are not easy to control. The energy load that is “over” in the beginning is wasted. No change to save it.


 

Conclusion

Think carefully when setting up a lighting installations maintenance plan. This starts already with the choice for the light source. LED Modules are highly efficient, are likely not failing and offer long lifetimes between 50,000h and 100,000h. The control possibilities are comprehensive. The luminaires overload, that needs to be installed to guarantee the end of lifetime illuminance levels, can be saved by light management systems. Regarding all the mentioned points, LED is the competing light source. The features are dominant over traditional light sources. LEDs leave their green footprint in a lot of projects showing the lighting quality and savings in electricity bills.

Take the chance and install or renew the lighting system by using energy efficient LED light sources and luminaires. Your world will be a greener place in the future. If you have further questions please contact the lighting experts at
MyLEDLightingGuide.com and discuss products as well as solutions.
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