Upgrading a building’s lighting system is one of the most cost-effective measures to improve energy efficiency. Reductions in energy use ranging between 25 and 35 percent are common; savings as high as 50 percent are possible. What’s more, a well-designed lighting upgrade can improve appearance, help to increase productivity and occupant comfort, enhance security and trim maintenance costs.
But not all lighting upgrades live up to their potential. Energy savings can be less than expected, or the new lighting may be too bright or too dark. What separates success from failure is often the level of understanding brought to an upgrade program. It’s important to be aware of common pitfalls that can reduce upgrade effectiveness.
Most commonly used when upgrading fluorescent lighting systems, one-for-one replacement upgrades reuse as much of the existing lighting system as possible. For example, lamps and magnetic ballasts are replaced with higher efficiency lamps and electronic ballasts. Existing fixtures and wiring are retained.
Reusing components does cut the cost of the upgrade. But this approach does not address such problems as lighting levels that are too high or too low or uneven distribution of light.
What’s more, reusing the existing fixtures can significantly reduce the overall efficiency of the upgraded system. As fixtures age, reflecting surfaces deteriorate, reducing the amount of light that reaches the occupied space. And one-for-one replacement doesn’t take advantage of new fixture designs that are more efficient and place more light where it is needed. That strategy also precludes installation of lighting controls. Nor can higher efficiency light sources be considered: As the efficiency of the light source increases, the number of fixtures required in a space drops, requiring that both fixtures and wiring be replaced.
A better approach is to start by evaluating the lighting needs in the space. Once those requirements are understood, the most appropriate type of lighting system can be selected.
One of the most common mistakes made when upgrading lighting systems is to assume that lighting levels must be reduced. The roots of this assumption can be traced back to the 1970s, when many facility executives removed lamps and fixtures to cut lighting energy requirements. That did reduce energy use, but it also created problems, including lighting levels that were too low for the tasks being performed and light distribution that was uneven.
The goal should be to provide the appropriate level of lighting in a given space during only those times when it is needed using as little energy possible. That means that the lighting upgrade must first address the issues of quantity and quality of light. Chances are some areas are overlit by the existing lighting system. Similarly, some areas will be underlit. If the new system is to be effective, it must provide the needed level of lighting in each area. Energy savings will be achieved by using the highest efficiency light source and control system, not by arbitrarily reducing lighting levels.
Another common mistake made when upgrading lighting systems is to overlook the value of effective lighting controls. Too often, high-efficiency light sources are connected to a manual switch. The result is that lights are often left on in unoccupied areas for hours at a time.
Effective control systems perform two tasks. First, they regulate light output to provide the level of illumination required to meet the needs of the activities performed in the space. Second, they limit the operation of the lighting system to times when light is needed. By performing these two tasks, lighting control systems can reduce total lighting energy use by 35 to 50 percent.
There are a range of lighting control options. Occupancy sensors can be installed in private offices, conference rooms and classrooms. Dimmable fluorescent ballasts can be used where lighting level requirements change with time.
Dimmable ballasts can also be used in daylit areas. In these applications, the system varies the amount of light produced by the fluorescent fixtures based on the amount of daylight available. Daylight dimming systems can reduce lighting energy requirements on average by 30 percent.
While it is important to consider lighting levels and energy efficiency, other issues also affect the quality of light, including glare, color rendering and apparent brightness.
Glare occurs when lighting fixtures fail to properly control downward light from a fixture. Good fixture designs reduce glare by balancing indirect lighting and downlighting.
Color rendering is a measure of how well a fluorescent lamp renders color in comparison to an incandescent lamp. The higher the color rendering index (CRI), the closer in color objects under the fluorescent lamps will appear to the same objects under incandescent lamps. Poor CRI values can interfere with tasks being performed, make it difficult to recognize faces and give spaces a poor appearance. High-quality fluorescent lamps will have a CRI of 70 or higher.
The smaller the light source, the greater its apparent brightness. Bulbs such as HID sources and T5 fluorescent lamps have a very high apparent brightness. The concern with high apparent brightness sources is glare. Fixtures that use bulbs of this type must be properly shielded.
Maintenance costs, such as relamping, replacing ballasts and cleaning fixtures, represent a significant portion of the total cost of system ownership. In general, costs will be reduced by upgrading to new light sources and fixtures but can be reduced even further by carefully selecting system components. Using programmed-start ballasts instead of instant-start ballasts will extend the life of frequently switched lamps. Minimizing the number of different lamp types and sizes will reduce inventory costs and allow lamps to be purchased in bulk.
Most programs will be justified on the basis of their cost savings. Because upgrade projects can be expensive and must compete for funding with other projects and programs, facility executives must provide estimates of expected savings. These estimates not only help secure funding but also aid in identifying the most cost-effective upgrade tasks and options.
To develop realistic estimates, facility executives must use the electricity rate structure that is in effect for the facility. The mistake many make is to use an average rate for electricity. That approach assumes either that electricity rates do not vary with the time of day or with the season, or that the number of hours that the lights are operated is equal in each rate’s time period.
The problem is that rate structures today are anything but constant. Compounding the problem is the fact that most building lighting systems are operated primarily when electricity rates are at their peak. Using an average rate for electricity under these conditions seriously underestimates potential cost savings.
To obtain the most accurate estimate of savings, facility executives must use the rate schedule in effect for the facility. Although this complicates savings calculations, it provides a better estimate of the cost impact of the upgraded lighting system.
Facility executives must understand that there is no universal best fit when considering lighting upgrades. Effective solutions in one building may not prove effective in another. The upgrade must be matched to the conditions of the facility and the needs of the building occupants. By carefully planning the upgrade program, facility executives can avoid lighting upgrade pitfalls.
Contributing editor James Piper, PE, Ph.D., is a consultant and writer with more than 25 years of experience in the facilities field.
