In a typical office building, lighting accounts for approximately 29% of the energy consumed. Efficient and appropriate lighting is a major factor in all successful and cost-effective facilities. Upgraded, energy efficient lighting systems can reduce excess heat and energy use and can improve lighting quality, thereby increasing occupant comfort and productivity.
But with all the types of lighting and lighting technologies out there, how do facility professionals choose the correct fixtures, bulbs, and arrangements? One approach requires a thorough and accurate assessment of building occupant needs as they fit into the confines of the facility’s budget.
In addition, the proper selection of lighting entails knowledge of any local, state, and federal energy regulations and codes. These can include minimum CRI (color rendering index) and lumens-per-watt ratings. (The more lumens per watt produced by a light source, the more efficient that light source.)
Lighting System Characteristics
An effective lighting system has the following characteristics:
- It provides the correct light levels for each task while minimizing glare.
- It does not interfere with visual perception or cause visual discomfort.
- It creates an aesthetically attractive work environment.
- It is designed with attention to life cycle costs, including purchase, installation, maintenance, and energy costs.
A properly designed lighting system increases worker productivity by reducing visual fatigue. It also heightens safety and security by eliminating shadows in work spaces and in unguarded areas.
Lighting systems are classified according to fixture arrangement and type. Creating an efficient lighting system requires an understanding of these characteristics so facility managers (fms) can make informed and well thought out decisions.
These systems can be arranged in one of two ways: uniform or non-uniform.
Uniform lighting illuminates an entire area at about the same level, using any type of lighting focus. Fixtures are normally placed at a maximum height and spaced evenly without regard for the location of desks or equipment within a space.
Uniform lighting systems are designed to accommodate spaces in which workstations and tasks are frequently relocated. This arrangement is regarded as the best approach for illuminating densely occupied areas of up to 100 square feet per worker. However, uniform lighting has one serious drawback: it often provides more light than is necessary, contributing to significant energy waste.
To make a uniform lighting arrangement as efficient as possible, lighting controls (such as occupancy sensors and dimmers) are a good option. These controls allow the output of a given fixture or a small group of fixtures to be adjusted according to need.
In a non-uniform light fixture arrangement, the placement of fixtures is determined by the location of workstations and machinery along with the nature of the tasks that will be performed in a given space. While most spaces have uniform lighting arrangements, under certain conditions, adequate illumination can be provided by non-uniform lighting, saving up to half the operating cost of a uniform lighting system. For example, if workstations are not close together (generally more than 12′ apart) and if workstations are rarely relocated, non-uniform lighting should be considered.
There are five primary lighting system types:
- Overhead Lighting;
- Task Lighting;
- Accent Lighting;
- Daylighting; and
- Outdoor Lighting.
Overhead (or ceiling) lighting systems can be installed in a uniform or non-uniform pattern. In a uniform lighting plan, fixtures are laid out in a sequential grid regardless of task location. On the other hand, a non-uniform overhead lighting plan bases fixture placement on workstation location. Each arrangement has its advantages and disadvantages in these scenarios.
Task lighting, also called localized lighting, is a low cost type of non-uniform lighting. This type of system can be anything from a desk lamp to a fixture located some distance away from a task.
While task lighting promotes worker productivity because the lighting can be tailored to the needs of each workstation, it is more difficult to control from a central location. In addition, task lighting produces more heat than other lighting sources, thus placing a higher demand on air handling systems.
Accent lighting, also called effect lighting and highlighting, can be used to add focal points and/or create a balanced level of light in a non-uniform lighting system. Selective illumination of walls can be used to create a dramatic effect or to increase the ambient lighting in a space.
Daylighting is the intentional use of light from windows or skylights. This type of lighting can increase occupant satisfaction and conserve energy if its glare and heat can be controlled. Although daylighting does not eliminate the need for fixtures, the natural light improves the quality of light in a space.
Many new buildings have incorporated the use of daylighting into their overall energy management systems through the use of louvers or screens, good E-rated (energy efficient) glass, and automated building control systems able to adjust automatically for the amount of daylight entering a space. To achieve this level of efficiency through daylighting, the orientation of the building, placement of walls, and other structural characteristics must be taken into account during the design phase of building construction.
In addition, the heat transmission of each window or skylight must be compared with its light contribution. Large glass areas intended to provide illumination can actually be energy inefficient. These areas increase building heat loss in cold months and increase heat gain in warm weather. Both of these conditions increase demands on the air handling system. Therefore, daylighting is most effective in mild climates where heat loss is not a major issue.
Thoughtfully designing an outdoor lighting system is an effective and relatively inexpensive way to enhance a building’s safety and security. An approach of this kind can save tremendous amounts of money by making costly liability claims against the property owner less likely.
Choosing The Right Lamp
There are several kinds of lamps, each with its own characteristics and uses. The three primary types are incandescent, fluorescent, and HID (high intensity discharge).
Incandescent lighting is the least efficient source of white light in common use, producing only 15 to 35 lumens per watt. (Regular incandescent bulbs produce 15 to 24 lumens per watt.) Only 10% of the energy consumed by incandescent lamps produces light; the other 90% produces heat.
This lighting is about 25% as efficient as fluorescent lighting and cannot economically provide the levels of light typically required in general office areas. Despite these drawbacks, this type of lamp is popular because of its low initial cost and good color rendering properties. Incandescent lighting may also be used to provide color effects or accents.
Tungsten halogen lamps are a kind of incandescent lamp, but they operate differently. The combination of a tungsten filament and halogen gas produces a clean, white light with very few lost lumens during the life of the lamp. These lamps operate at higher temperatures than standard lamps, so quartz rather than glass is used for the bulb. They have an efficiency of 19 to 35 lumens per watt.
Fluorescent lighting provides more than two-thirds of all the electric illumination (and most of the general office lighting) in the U.S. Its popularity is due to the lamp’s low brightness, high efficiency, long life, and low overall cost. The efficiency range for fluorescent lamps is from 50 to 100 lumens per watt.
Compact fluorescent lamps initially cost more than incandescent lamps, but the energy and maintenance cost savings over time make fluorescent lamps a better investment.
In addition to long life and efficiency, fluorescent lamps come in a wide variety of configurations and shapes. Fluorescent tubes commonly vary in length from 6″ to 8′. They are available in linear, circular, U-shaped, compact, and twin- or quad-tube forms.
One of the most widely used fluorescent lamps is the 40W T-12. (The T refers to the tubular shape; the numerical designation indicates the diameter in eighths of an inch. For example, a T-12 bulb has a diameter of 1.5″)
However several 4″ lamps have been developed to replace this standard. These retrofit possibilities include:
- Energy saving 34W T-12 lamps;
- Energy saving 32W T-12 lamps;
- 40W T-10 lamps; and
- 32W T-12 lamps.
Each of these retrofit lamps has specific requirements to assure compatibility; therefore fms must read the manufacturer’s instructions thoroughly before attempting an exchange.
Fluorescent lamps do have some disadvantages. They have a high initial cost because of the required auxiliary equipment, such as a ballast starter.
They are also affected by ambient temperature. For example, low temperatures lengthen starting time and reduce light output considerably. Some of this loss can be overcome by using low temperature ballasts and tubes, but this solution costs more. Consequently, using fluorescent lighting in cold, outdoor environments, such as parking areas, is not practical.
HID lamps used for general lighting include mercury vapor, metal halide, high pressure sodium (HPS), and low pressure sodium (LPS). While these lamps vary widely in efficiency, their rated lives are comparable to fluorescent lamps.
Mercury vapor lamps are the earliest form of HID lamps and can be used either indoors or outdoors. Although they are not very efficient, lamp life is generally good; they produce 30 to 60 lumens per watt and last between 16,000 and 24,000 hours. Lamps that are burned continuously last longer.
Mercury vapor lamps come in several colors each with different color rendering properties. However, the light output of this type of lamp decreases substantially near the end of its life.
Metal halide lamps are similar to mercury vapor lamps and can also be used for both indoor and outdoor applications. Although metal halide lamps are more efficient—producing 80 to 125 lumens per watt—and have better color rendering than mercury vapor lamps, their rated life is only 6,000 to 20,000 hours. Furthermore, the operating position (vertical or horizontal) of some metal halide lamps is limited and should be checked before installation.
HPS lamps are the most efficient white light source, producing a warm, golden color. They are used extensively in many outdoor applications and for industrial lighting indoors. These lamps are also used in commercial interiors, although their color is generally not as acceptable as that of fluorescent lamps.
HPS lamps produce 40 to 140 lumens per watt, and this efficiency rating can be increased by using higher wattage lamps. Their rated life—16,000 to 24,000 hours—is longer than that of metal halide lamps. Although a lamp with improved color is available, its light output is lower and its rated life is shorter than that of standard high pressure sodium lamps.
LPS lamps have very poor color rendering properties because they produce a bright yellow light—all colors appear as black, white, or shades of gray. Therefore, they should only be used where the appearance of people and color is not important (in parking areas, for example). Despite this, the efficiency is high—120 to 180 lumens per watt—with an acceptable rated life of 12,000 to 18,000 hours.
Armed with this information, fms should be in a better position to assess their current lighting system and the lamps being used. If minor changes are in order, this outline can assist in the creation of a preliminary plan for modifying existing lighting system components. For new projects (or more extensive overhauls), the assessment can be used as a part of a new lighting plan.
Regardless of the scope of the project, fms must remember to take into account not only the costs and efficiencies of each lighting component, but also the needs of the building’s current and future occupants. When properly managed in balance, these factors can fundamentally contribute to the success of the facility.
Mairs is a former project editor for the BOMI Institute, based in Arnold, MD. Questions regarding this article can be sent to firstname.lastname@example.org.