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Group relamping, rated life, and economic life of lighting systems
Robert Bresnahan., Larson Electronics

A significant portion of the costs associated with industrial and commercial lighting systems comes from the need for regular maintenance of these systems. Effective lighting must do more than simply illuminate the targeted area, they also play a direct role in efficiency, task performance, safety, and more. When first installed a lighting system will perform to best of its potential, but this performance can drop off significantly over time, which in turn can have a detrimental effect on business performance that can be difficult to notice and gauge because of how this drop occurs incrementally. For most of us, a lamp fails when the bulb burns out, but for industry lamp life is not determined simply by lamp failure, but by the lamps “economic life”. Determining a lamps economic life and scheduling maintenance around it ensures consistent peak lighting system performance and thus helps reduce losses and operating costs over the long term.

Rated life and economic life are two different things and are not interchangeable. Rate lamp life generally refers to the average amount of time before a lamp is expected to stop operating. Economic life on the other hand takes into account factors such as lumen output, color quality, and operating efficiency. Economic life is determined by the point at which a light begins to exhibit significant reductions in these performance parameters and is generally accepted to be an average of 60% of the rated life of a lamp.

Unlike home and residential lighting where it is most economical to perform spot replacements as lamps fail, industrial and commercial sectors benefit most from group relamping. Large facilities relying on metal halide lighting perform best when lighting systems are at their peak performance. By the end of these lamps rated life however, output drops significantly, as much as 40%. Additionally, as metal halide lamps age they exhibit significant color shifting, that is, the color temperature of the light changes as well. This is why it is not uncommon to see stadiums or warehouses for example with several lamps appearing to glow a pink or reddish color while others are producing bright white output. Those colored lamps have reached then of their useful life and thus are due for replacement. When many lamps begin to display dimmed output and color shifting, they reduce overall illumination as well as degrade overall light quality. This can have an adverse effect on worker performance, workplace safety, and customer perceptions of the location.

Group relamping should be performed according to lamp economic life and essentially refers to the process of performing maintenance on a comprehensive level, replacing as many lamps as needed if not all in order to maintain overall output and light quality at peak levels while addressing the rest of the lighting system as well. Although lamps may still be operational, and even appear to be operating correctly, replacing lamps according to economic life and rated life is more cost efficient. The reasons for this are many, and primarily consist of savings found through less frequent maintenance intervals and maintained peak performance.

In most cases, particularly with large scale applications, the most effective maintenance solution involves contracting maintenance to outside professionals. Since on site workers may not be qualified to service high power lighting systems, and time spent away from their normal tasks spent servicing lighting represents lost productivity, outside contractors make the most practical sense. For those who perform their own servicing in house however, group relamping still remains the most cost effective option as the benefits found with a lighting system operating at peak performance still remain.

First and foremost, group relamping keeps the system working at peak output. Newly installed systems obviously operate at peak performance. Performance drops as the lights age however, and by the time they near the end of their rated life, most standard metal halide lights will have lost 40 to 50% of their original light output. The mount of degradation that takes place is dependant on many factors, and drop off can be lower or higher, but when we perform servicing before the lamps reach the end of their rated life and instead focus on servicing according to economic life, we avoid reaching this state of
output decline. Additionally, group relamping allows us to address the system as a whole on a consistent basis, performing fixture cleaning, repairs to damaged fixtures, and perform system inspection on a comprehensive basis. As a result, potential future problems are found and avoided and the cleaner fixtures run cooler which helps to improve lamp longevity, thus reducing costs. It is also important to note that by maintaining the system at optimum levels we also maintain the aesthetic appearance of the area as well as the security and safety that a well lit work space helps to foster.

Consistent color temperature is another important factor group relamping addresses. As mentioned earlier, most metal halide and fluorescent light systems experience color shifting over the life of the lamp. When we spot replace lamps, the result is a mixture of lamps operating at the correct color temperature while others display reduced light quality. This creates an environment where light quality and performance varies from one part of a facility to the next. When a program of group relamping is followed however, all of the fixtures in a location tend to experience color shifting at a more uniform rate, and when we perform service according to economic life rather than rated life, color shifting is reduced to minimal occurrences and uniform performance maintained.

As light output from metal halide and other HID light sources declines, efficiency is adversely affected. A lamp will consume the same amount of electricity, but since lumen output and color quality has degraded, the light is no longer maintaining an efficient lumen to watt ratio. Additionally, many HID light systems such as metal halide can actually consume more electricity as lumen output goes down, further reducing efficiency and increasing costs associated with energy consumption. Group relamping prevents
this efficiency drop, thus maintaining the energy efficiency of the lighting system as a whole and keeping costs consistent and low.

Although group relamping might initially seem more costly initially, the savings are realized over the course of annual operation. A servicing plan built around the economic life of the fixtures reduces costs incurred from downtime and the labor needed to make repairs, and prevents the need to frequently
take employees away from their normal duties in order to perform servicing when lamps burn out. The benefits of group relamping include consistent optimal light output and quality, consistent worker productivity and safety, and higher efficiency leading to lower energy costs.

Article provided by Robert Bresnahan of Larson Electronics.