Degradation of Illumination Systems

Maintenance Factor

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. 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 luminaries 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 luminaries 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? Different factors influence the decrease in lighting level like the soiling of the room surfaces, the soiling of the luminaries, 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. Luminaire Maintenance Factor: The luminarie maintenance factor is the ration of the luminaries luminous flux before and after cleaning. It depends on the luminarie construction and design (open housing or closed one) as well as on environmental conditions (dirty or clean). 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. 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. 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. MF_ExampleOpenPlanOffice

A maintenance factor of 0.8 shows, that the new lighting system needs to be over driven by 25% not to undercut the minimum required illumination level after 10 years. 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. 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 efficient, likely not failing and offer long lifetimes between 50,000h and 100,000h. The control possibilities are comprehensive. The luminaries 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. Take the chance and install or renew your lighting system by  energy efficient LED light sources and luminaries. If you have further questions please contact the lighting experts at and discuss products as well as solutions.