Lighting systems are a major component in building energy use. In non-industrial facilities, lighting energy use averages nearly 35 percent of all building electrical energy use. And this does not factor in the additional energy that must be used to remove the heat generated by the lighting system. With such a large component of energy use concentrated in one system, it is not surprising that hundreds of millions of dollars have been spent upgrading building lighting systems to improve operating efficiency

While nearly all lighting system upgrades produce large savings when they are new, some facility executives have found that the savings don’t last. In these facilities, lighting energy use slowly increases over time. And although it may remain well below its original level, it is still significantly higher than when the system was new. The result is that the investment in the upgrade is not delivering on its promise of savings.

When facility executives investigate why the savings have decreased, they find a number of things have happened. Building occupants may have felt that the level of lighting provided by the new system was inadequate, so they have installed additional lighting fixtures. The level of control over the operation of the lights may also have been inadequate, resulting in large areas being illuminated for only a small number of occupants. Or perhaps the type of controls installed were not well-suited for the operations taking place in the facility, so they were modified or bypassed by the building occupants. In still other cases, building occupants or maintenance personnel believed that the use of the lighting controls would shorten the life of the lamps and increase maintenance costs, so the controls were bypassed.

Avoiding these and other problems is essential to maintaining the operating efficiency of the lighting system over its life. Avoiding problems that reduce the long-term operating efficiency of the lighting system requires involvement by the facility executive both before the system is designed and after it is installed. It is this involvement that will help ensure efficiency gains from lighting system replacement programs last the life of the system.

The long-term energy savings of a lighting system replacement project are directly related to the level of effort that goes into planning the system replacement program. Selecting a particular solution without fUlly understanding the lighting needs and options available will limit both the performance of the new system and the long-term savings the system can produce. Similarly, simply replacing existing fixtures with new, energy-efficient fixtures without considering its effect on the quantity and quality of light required in the space will perpetuate or amplify existing lighting problems.

Successful lighting projects start with an understanding of the lighting requirements of the building occupants based on the activities being performed. Lighting requirements are more than foot-candles. They include not only how much light but also the quality of the light needed, where it is required and when it is required.

An effective lighting planning tool is the lighting system inventory. The lighting system inventory is a detailed survey of the facility that is used to determine the lighting requirements of all spaces. It identifies what is installed where, how it is controlled, and when lighting is required. It then identifies areas where the existing lighting system fails to meet the needs of the occupants or requires excessive energy to operate.

One of the most important factors in maintaining the long-term efficiency gains achieved by a lighting retrofit project is flexibility. Facilities are in a constant state of change. People move. Functions change. Lighting needs change. If the facility’s lighting system is to continue to meet the needs of the occupants, it too must have the ability to change.

A lighting system that cannot be readily modified with changes in use of the facility will result in areas that are over- or under-illuminated, or lack the proper controls to meet the lighting requirements of the occupants. The net result of this mismatch will be the addition of new lighting fixtures and the bypassing of lighting controls, both of which decrease the operating efficiency of the system. Building in flexibility during the planning stage will allow fixtures to be moved, added or deleted as required when changes take place.

Long-term Gains
The planning stage is also the time to consider how the new lighting system will be maintained — one of the most important factors in determining the long-term efficiency of the system. Good maintenance practices will limit light losses due to depreciation of the lamps and fixtures, and accumulation of dirt on fixture surfaces. But good maintenance practices require that the fixtures be readily accessible for maintenance and easily maintained. It is an iron law of maintenance that if something cannot be readily maintained, maintenance will be deferred.

For lighting systems, deferred maintenance can mean lower lighting levels, the need to add additional fixtures and a loss of long-term efficiency. Maintenance must be planned. All lighting fixtures must be accessible and easy to clean. Lamps must be easily reached and easy to change. Limit the number of lamp types used so that it is easy to maintain a stock of replacement lamps.

It is also important to plan for lighting controls. Too often, attention in new lighting system designs is focused on the efficiency of the lamp and control of the lamp is overlooked. Installing good lighting controls is at least as important as installing the highest efficiency suitable light source. Without proper controls planned into the system, lights will operate when they are not required, decreasing the efficiency of the lighting system.

Finally, the planning stage for a new lighting system should provide a realistic estimate of savings. Too often, unrealistic figures are cited for potential energy savings. These unrealistic figures often result from the false assumptions and misunderstandings about how the system will be used by the occupants. By first developing an understanding of the building occupants’ lighting needs, a more realistic estimate of the potential savings the system can provide will be made.

Operational and Maintenance Practices
Effective planning is a necessary step in maintaining lighting efficiency gains, but it is not the only step. Lighting systems, like other building systems, require ongoing attention. If the lighting system is to maintain efficiency gains over its expected life, facility executives must implement a number of operational and maintenance practices.

The first step that should be taken once the system is installed is to meet with building occupants to discuss the new system and its operation. Often, people fail to fUlly understand the purpose and the impact of components of the lighting system. For example, when occupancy sensors are installed, there is a widespread belief that the more frequent starting of the lamps will reduce lamp life, increasing overall operating costs. As a result, many of the controls are bypassed.

In reality, though some lamp life may be sacrificed for energy savings, energy savings typically exceed the cost of the lost lamp life by a factor of 10 or more. If the efficiency gains from limiting the operating time of the lamps are to be realized, it is important that both the building occupants and maintenance personnel understand the benefits of using the occupancy sensors or other lighting controls.

One of the most important activities that can be performed on a lighting system is programmed maintenance. From the moment that a lighting system is installed, its performance declines. The light output from the lamps decreases as the lamps age. The lenses discolor, decreasing light output. Dirt accumulates on lamp and fixture surfaces, further decreasing light output. The net result is a decrease in light output with no decline in energy use.

Without programmed maintenance, this light output will continue to decline and will result in areas being under lit. Building occupants, in response to these under lit conditions, may decide to bring in their own task lighting, which may well have a lower operating efficiency than the primary lighting system. As a result, overall lighting system efficiency decreases while energy use rises.

There are two primary elements in programmed lighting maintenance that can be used to help maintain system operating efficiency over time: group relamping and group cleaning.

Group Relamping
Most facilities still replace lamps on a spot basis as they burn out. Managers of these facilities reason that they are reducing lamp costs by waiting until the lamps fail before they are replaced. What they don’t realize is that by replacing lamps on a spat basis, they are increasing the overall cost of their lighting maintenance and decreasing the performance and efficiency of their lighting system.

For example, switching from a program of spot replacement for burned out lamps to one where all of the lamps in a given area are replaced at the same time reduces labor costs, on average, by a factor of five. The cost of the lost lamp life is very small in comparison to the labor savings.

For the long-term efficiency of the lighting system, implementing a group relamping program is critical. As lamps age, their light output decreases as a result of deterioration of the phosphors within the lamp. While the rate of deterioration is slow, it is significant. For example, by the time a typical fluorescent lamp reaches its expected life, its light output has been decreased by 20 to 30 percent, with no reduction in energy use.

If lamps are replaced on a spot basis, then overall lighting levels in the room will be reduced, sometimes by as much as 20 percent, because of the various ages of the lamps installed.

One of the goals of a group relamping program is to replace the lamps before their light output has fallen significantly. The recommended replacement interval is 70 percent of rated life. At that point, lamp failures are still relatively low and the light output of the lamps is nearly 90 percent of what it was when the lamps were new. The result is higher lighting levels with no increase in energy use, lower maintenance costs and long lamp life.

Cleaning lamps, fixtures and fixture diffusers is an important element in maintaining the long-term efficiency of any lighting system. All lighting fixtures accumulate dirt over time. The rate at which they accumulate dirt depends on the type of fixture and the environment in which it is installed. Dirt, by blocking the transmission of light from a fixture, decreases the light output of a system, reducing its efficiency. Unfortunately, like group relamping, few facilities have implemented a scheduled fixture cleaning program. It is not uncommon to find that 20 percent of the light produced by a fixture is lost to dirt in a typical office environment that does not have a scheduled fixture cleaning program.

Implementing a scheduled cleaning program is the only way to avoid the efficiency losses resulting from the accumulation of dirt. Like group relamping, cleaning is most effectively and efficiently performed when all fixtures in a particular area are cleaned at the same time. Many facilities find that it is most convenient to schedule fixture cleaning at the same time that the fixtures are group relamped. Depending on how rapidly the fixtures accumulate dirt, it may be necessary to schedule an additional cleaning at the midpoint between scheduled relampings.

The final element in maintaining lighting system efficiency gains is the periodic walk-through inspection of all areas in the facility. In addition to identifying maintenance problems that are occurring with lighting equipment, the walk-through will identify areas where changes in building occupant activities require changes be made to the lighting system.

Facilities are in a state of constant flux. If the lighting system is to retain its efficiency, it must be modified to match the needs of those changes.


First published February 2000