Although daylighting is the most energy-efficient and preferred method of illuminating a building, it is not always adequate or available. See the Daylighting section for more information on using natural light. Electric lighting should be designed to supplement daylight and provide appropriate light levels for particular spaces. Residential, commercial, industrial, and retail facilities each use several different electric light sources. The purpose of this section is to provide a brief overview of some basic lighting fundamentals related to design, technology, and terminology, with special emphasis given to energy-efficient systems and technologies.

Also see the Green Building Factsheets for introductions to this and other green building topics.

When designing electric lighting for a particular space, both quantity and quality of light need to be considered. Both if these issues will be determined by considering many factors, including room/building layout, hours of occupancy, type of activity in the space, and age of occupants.

Quantity

Avoid overlighting a space. In the past, there was a misconception that the more light in a space, the higher the quality. Not only does overlighting waste energy, but it can also reduce lighting quality. Begin by using The Illuminating Engineering Society of North America procedure for determining the appropriate average light levels for a particular space. Then, select the appropriate type and quantity of lamps and light fixtures based on the following criteria:

• fixture efficiency
• lamp lumen output
• reflectance of surrounding surfaces
• light losses from lamp lumen depreciation and dirt accumulation
• room size and shape
• availability of natural light.

Quality

With regard to quality of illumination, there are three issues that should be considered: glare, uniformity of illumination, and color rendition. Glare has become a much larger concern than in the past due to the increased use of computer display terminals in the workplace. Glare is a visual discomfort caused by an excessive bright light source. A bright object in front of a dark background usually will cause glare. Too much contrast causes glare and makes visual tasks more difficult.

The uniformity of illuminance addresses how evenly light is spread over a task area. Two factors may compromise uniformity: improper fixture placement, and fixtures that are retrofitted with reflectors that narrow the light distribution.

Light sources vary dramatically in their ability to accurately reflect the true colors of people and objects. A measure of this ability is the color-rendering index (CRI). The color-rendering index is a scale from 1-100, where higher CRI represents better color rendering. CRIs in the range of 75 to 100 are considered excellent, 65-75 good, 55-65 fair, and 0-55 poor. Both daylight and incandescent light is considered ideal, with a CRI of 100.

Light source selection

Selection of the appropriate electric light source depends on installation requirements, life-cycle cost, color qualities, dimming capability, and the effect desired. Three types of lamps commonly used are incandescent, fluorescent, and high intensity discharge consisting of mercury vapor, metal halide, high-pressure sodium, and low-pressure sodium. Each light source has its own unique characteristics of efficiency, color temperature, and color rendering index, making some lamps more appropriate for certain applications than others. This is shown in Table 1.

Some lamp types are more efficient in converting energy into visible light than others. The efficacy of a lamp, measured in lumens per watt, refers to the number of lumens leaving the lamp compared to the number of watts required by the lamp and ballast. Sources with higher efficacy require less electrical energy to light a space. Color temperature (CT) is more of an architectural choice and is a measurement of the "warmth" or "coolness" produced by the lamp. Lower CT light sources give a yellowish, "warm" light, while high CT sources produce a blueish, "cool" light. Lower color temperatures (warmer sources) are usually preferred in lower illuminance environments such as dining areas and living rooms and higher color temperatures (cooler sources) are usually preferred in higher illuminance environments such as grocery stores and drug stores. Triphosphor lamps with 3500K-color temperature are considered neutral and are usually preferred in office and retail use.

All light sources gradually dim to some degree as they are used. Lumen maintenance refers to a lamp's ability to produce light well into its operating life. A lamp that produces nearly the same amount of lumens at the beginning and end of its life is said to have a high lumen maintenance.

All fluorescent and HID lamps require ballasts as an integral component of the lighting system. Fluorescent ballasts can either be magnetic or electronic. The old standard core-coil magnetic ballast is no longer available in the US. It has been replaced with the high-efficiency core-coil and the cathode cutout or hybrid. The high-efficiency ballast replaces the aluminum wiring and lower grade steel of the old standard ballast with copper wiring and enhanced ferromagnetic materials. The result of these material upgrades is a 10 percent system efficiency improvement.

Cathode cutout or hybrid ballasts are energy-efficient core-coil ballasts that incorporate electronic components. These components cut off power to the cathodes after the lamps are lit, resulting in an additional 2-watt savings per standard lamp. Full-output T8 hybrid ballasts are nearly as efficient as rapid-start two-lamp T8 electronic ballasts.

Electronic ballasts improve fluorescent system efficiency by converting the standard 60 Hertz input frequency to a higher frequency, usually 25,000 to 40,000 Hz. Lamps operating at these higher frequencies produce about the same amount of light, while consuming 12 to 25 percent less power. Other advantages of electronic ballasts include less audible noise, less weight, virtually no lamp flicker, and dimming capabilities (with specific ballast models).

Most magnetic ballasts have a ballast factor between 0.93 - 0.95. The ballast factor is the percentage of the lamps" total rated lumens produced by the specified lamp-ballast combination. Thus, a ballast with a ballast factor of 0.90 will drive the lamps with enough electric current to produce 90 percent of the light they are capable of producing. Electronic ballasts are available in a wide range of ballast factors. You can purchase them with a high ballast factor (1.00 - 1.30), which overdrives the lamps to boost light output, or you could specify a low ballast factor (0.47 - 0.80) to reduce light output and energy consumption. Full output electronic ballasts have ballast factors that exceed a minimum of 0.85.

Table 1: Comparison of Common Light Sources

Incandescents

Incandescent lamps are one of the oldest and least energy-efficient electric lighting technologies available. Lamp efficacies range from 6 to 24 lumens per watt. Lamp life is also quite short relative to other electric light sources, as seen in Table 2. The common household incandescent lamp, also referred to as an "A-lamp" in the lighting industry, has a rated life of only 750 hours. Improvements in manufacturing technology have led to reduced wattage lamps, which are offered by several manufacturers, using approximately 15 percent less power.

Incandescent lamps with reflectors have improved light output. Ellipsoidal reflector (ER) lamps outperform reflector (R) lamps because of the way the light is reflected out of the fixture. Parabolic aluminized reflector (PAR) lamps are available with improved performance from reflector designs. PAR lamps are suitable for exterior applications.

The tungsten-halogen lamp is the most efficient type of incandescent. The presence of halogen gas within the bulb produces more light, with less energy use, as well as increasing the rated life of the lamp (1000-5000 hrs). A tungsten-halogen consumes about 30 percent less power than a standard A-lamp. Compact halogen lamps are popular for display and accent lighting. Increased efficiency tungsten-halogen lamps are now available which use an infrared coating on the quartz bulb or an advanced reflector design to redirect the infrared light back to the filament. The filament then glows hotter and the efficiency of the source increases. Halogen lamps are available with wide and narrow beam spread.

Diodes and thermisters are electronic components that can be added to incandescent lamps to improve their efficiency. Diodes are wave rectifiers that cut 60-hertz AC cycles in half. The results are similar to using a dimmer. Although power consumption is reduced by 42 percent, light output is reduced by 70 percent. Lamp life is typically extended but color rendition is poor and the economics are generally unfavorable. Thermisters limit the inrush current and reduce the voltage. Power consumption is reduced by 2-4 percent and light output is reduced by 7-16 percent.

Whenever feasible, you should seek alternatives to incandescent lamps. With recent advances in compact fluorescents and halogen lamps, the use of standard incandescent lamps is difficult to justify.

Fluorescent Lamps

Fluorescent lamps are the most commonly used commercial light source in North America. Their popularity can be attributed to their relatively high efficacy, diffuse light distribution, and long operating life. Improvements in the phosphor coating of fluorescent lamps have improved color rendering and made fluorescent lamps acceptable in many applications previously dominated by incandescent lamps.

Fluorescent lamps are available in several shapes, including straight, U-shaped, and circular configurations. One of the most common lamps is the four-foot (F40), 1.5" diameter (T12). More energy-efficient, 1" diameter (T8) lamps are now the industry standard. Because the T8 lamps operate at reduced current (256mA), they require a compatible ballast. T8 lamps with electronic ballasts produce from 90 to 100 lumens per watt. The triphosphor coatings used in T8 lamps significantly improve color rendition. Lamp flicker, commonly associated with fluorescent lamps, is eliminated with the use of T8 lamps and electronic ballsts. Fluorescent lamps are now available with reduced mercury content. T5 lamps, 5/8" diameter, are the newest technology but not yet considered an industry standard.

Compact Fluorescent Lamps

Compact fluorescent lamps (CFLs) are energy-efficient, long lasting substitutes for incandescent lamps. They are no longer considered a new technology. They are available in many configurations and wattages, and can be purchased with lamp and ballast as an all-in-one piece or two separate components. The advantage of separate lamps and ballasts results from the difference in life expectancy of the two components. CFL lamp life is usually rated around 10,000 hours and ballast life is typically 20,000 hours. Thus, when the lamp burns out it can be replaced without having to replace the ballast as well. Several retrofit adapters are available for convenient retrofit in existing incandescent sockets. CFLs are available in many choices of luminaires including downlights, surface lights, pendant luminaires, task lights, compact troffers, sconces, exit lights, step lights, and floodlights. Dimming CFLs have also appeared on the market in the last few years, increasing opportunities for incandescent replacements.

High Intensity Discharge (HID) Lamps

HID lamps are similar to fluorescents in that an arc is generated between two electrodes. Originally developed for outdoor applications, HID lamps are also used in office, retail, and other indoor applications. HID lamps require time to warm up, usually from 2 to 6 minutes depending on the lamp. HID lamps also have a fairly long restrike time, from 5 to 15 minutes, depending on which source is being used. Therefore, good applications are areas where lamps are not switched on and off intermittently.

Mercury vapor lamps have the lowest efficacy of the HID family, rapid lumen depreciation, and a low CRI, as can be seen in Table 2. Because of these characteristics, mercury vapor lamps would not be a green choice.

Metal halide lamps are similar to mercury vapor but use metal halide additives inside the arc tube along with mercury and argon. The efficacy of metal halide lamps ranges from 50 to 115 lumens per watt. Wattages range from 32 to 2,000, offering a wide range of indoor and outdoor applications. Because of their good color rendition and high lumen output, these lamps are well suited for sports arenas and stadiums. Indoor uses include large auditoriums and convention halls.

High-pressure sodium (HPS) lamps differ from mercury and metal halide lamps in that they do not contain starting electrodes; the ballast circuit includes a high voltage electronic starter. They are filled with xenon to help start the arc, as well as a sodium-mercury gas mixture. HPS lamps are widely used for outdoor and industrial applications. The efficacy of the lamp is very high - as much as 140 lumens per watt. Although HPS lamps are not generally recommended where color rendering is critical, HPS color rendering properties are being improved. Some HPS lamps are available in "deluxe" and "white" colors that provide higher color temperature and improved color rendition. The efficacy of low-wattage "white" HPS lamps is lower than that of metal halide.

Low-pressure sodium (LPS) lamps are included in the HID family even though they are similar to fluorescent systems because of their low pressure. LPS lamps are the most efficacious light sources, but they produce the poorest quality light of all the lamp types. Since they are a monochromatic light source, all colors appear black, white, or shades of gray under an LPS source. LPS lamp use is generally limited to outdoor applications such as security or street lighting and low-wattage indoor applications such as stairwells. Lower mounting heights will provide better results with LPS lamps since they are less effective in directing and controlling a light beam, compared with "point sources" like HPS and metal halide.

Lighting Controls

Reducing operating hours through automatic lighting controls is a simple strategy to maximize energy savings.

Occupancy sensors save energy by automatically turning lights off in spaces that are unoccupied. Most occupancy sensors have adjustable settings for both sensitivity and time delay. Some occupancy sensors provide daylight switching with their occupancy sensing control. Occupancy sensors use two motion-sensing technologies: passive infrared and ultrasonic. Many manufacturers combine these two technologies into one product - a dual technology sensor.

Besides occupancy sensors, scheduling controls can help eliminate unnecessary use of lighting. Timed switching controls can be installed to ensure that lighting systems are turned off or dimmed according to an established schedule. These devices range from simple timers to sophisticated programmable systems. Photocells may also be used to automatically turn off lighting systems when sufficient daylight is available. All outdoor lighting should be controlled using a daylight switching system. For applications where outdoor lighting is not needed for dusk-to-dawn illumination, a timed-switching system can be wired in series with a photosensor.

Dimming controls can be used to vary the intensity of lighting system output based on ambient light levels, manual adjustments, and occupancy. Daylight dimming systems consist of photosensors that are wired directly to dimmable electronic ballasts. See the Daylighting section for more information on daylight dimming systems.

Panel-level dimming is a strategy that involves installing a control system at the electric panel to uniformly control all light luminaires on the designated circuits. Panel-level dimming is appropriate for dimming HID systems as well as both electronically and magnetically ballasted fluorescent systems. Continuous dimming is accomplished using a variable voltage transformer that reduces the voltage to the HID or fluorescent circuit. Another method of dimming HID fixtures is with the use of occupancy sensors in conjunction with HID bi-level luminaires. Common applications include parking lots, athletic facilities, and warehouse aisles.

Another "control" for lighting is the prevention of "light trespass" from exterior lighting. Light trespass is the situation where light falls in unintended areas, such as neighboring properties or up into the night sky. Several methods of shielding, hooding, and directing light are available, and should be considered when planning outdoor lighting. Not only is light trespass a waste of energy, but also undirected outdoor lighting can interfere with bird migration and kill birds. It can also interfere with insect pollination for crops, as well as affect human health.

Table 2: Performance of Common Light Sources

See "Lighting Consultants" in Yellow Pages

Clanton & Associates, Inc.
4699 Nautilus Ct. Ste. 102
Boulder, CO 80301
(303) 530-7229
www.clantonassociates.com

Powell Engineering LLC
Douglas Powell, P.E.
1700 Patterson Road
Austin, Texas 78733
(512) 263-5455

Environmental Depot
Jon and Alyssa Alvord, Owners
9914 Highway 290 West
Austin, TX 78736
(512) 288-6161 Toll free: (877) 258-6161
info@ed-austin.com
www.environmentaldepot.com

Good Common Sense.net
Christopher Searles, Owner
chris@goodcommonsense.net
www.goodcommonsense.net
(347) 623-8131

Caltex Efficient Energy
Douglas E. Duschatko
413A W. Johanna Street
Austin, TX 78704
(512) 535-1253
dougd@caltexefficientenergy.com
www.caltexefficientenergy.com

Elflist.com
www.elflist.com
Seattle City Light website guide to efficient lighting fixtures

Illuminating Engineering Society of North America
120 Wall St., 17th Floor
New York, NY 10005
(212) 248-5000
www.iesna.org

Lighting Research Center
Rennselaer Polytechnic Institute
21 Union St.
Troy, NY 12180
(518) 687-7100
www.lrc.rpi.edu

Litetronics International, Inc.
www.litetronics.com
Local Distributor: Brian Lewis
M&A Railroad
6704 East Park Dr.
Fort Worth, TX 76132
(817) 361-7923
eastwind@charter.net
Manufacturer of "Micro-Brite" dimmable compact fluorescent lamps

Lighting Simulation Software:

ADELINE
Lawrence Berkeley National Laboratory
Building Technologies Program
Mail Stop 90-3111
1 Cyclotron Rd.
Berkeley, CA 94720
(510) 486-7916
www.radsite.lbl.gov/adeline
Daylighting, electric lighting and whole building analysis, provides 3-D CAD modeling of a space, automatically generates SuperLite and Radiance input files, calculates interior luminance levels.

Lightscape
Discreet
10 Duke St.
Montreal, Quebec, H3C 2L7 Canada
(800) 964-6432
www.lightscape.com
Lighting design tool with high quality visual simulation.
Local sales:
Austin Business Computers, Inc.
3660 Stoneridge Rd., Bldg.F, Ste. 101
Austin, TX 78746
(512) 328-4747
www.ausbcomp.com

Lumen Micro 7.5
Lighting Technologies, Inc.
1630 Welton St., Ste. 400
Denver, CO 80202
(720) 891-0030
www.lighting-technologies.com
Graphics oriented indoor lighting design that analyzes complex interior lighting systems, including sidelighting, direct/indirect lighting, mixed, and even aimed luminaires. User-friendly input

RADIANCE
Lawrence Berkeley National Laboratory
Building Technologies Program
http://radsite.lbl.gov/radiance/
A suite of programs designed at Lawrence Berkeley National Labs for the analysis and visualization of lighting in design. Input files specify the scene geometry, materials, luminaires, time, date and sky conditions (for daylight calculations). Calculated values include spectral radiance (i.e. luminance + color), irradiance (illuminance + color) and glare indices. Simulation results may be displayed as color images,numerical values and contour plots. Radiance has no limitations on the geometry or the materials that may be simulated. Radiance predicts illumination, visual quality and appearance of innovative design spaces, and can evaluate new lighting and daylighting technologies.