The most common measure of light output (or luminous flux) is the lumen. Light sources are labeled with an output rating in lumens. For example, a T12 40-watt fluorescent lamp may have a rating of 3050 lumens. Similarly, a light fixture's output can be expressed in lumens. As lamps and fixtures age and become dirty, their lumen output decreases (i.e., lumen depreciation occurs). Most lamp ratings are based on initial lumens (i.e., when the lamp is new).
Light intensity measured on a plane at a specific location is called illuminance. Illuminance is measured in footcandles, which are workplane lumens per square foot. You can measure illuminance using a light meter located on the work surface where tasks are performed. Using simple arithmetic and manufacturers' photometric data, you can predict illuminance for a defined space. (Lux is the metric unit for illuminance, measured in lumens per square meter. To convert footcandles to lux, multiply footcandles by 10.76.)
Another measurement of light is luminance, sometimes called brightness. This measures light "leaving" a surface in a particular direction, and considers the illuminance on the surface and the reflectance of the surface.
The human eye does not see illuminance; it sees luminance. Therefore, the amount of light delivered into the space and the reflectance of the surfaces in the space affects your ability to see.
Refer to the GLOSSARY at the end of this document for more detailed definitions.
For example, to light a space that uses computers, the overhead light fixtures should provide up to 30 fc of ambient lighting. The task lights should provide the additional footcandles needed to achieve a total illuminance of up to 50 fc for reading and writing. For illuminance recommendations for specific visual tasks, refer to the IES Lighting Handbook, 1993, or to the IES Recommended Practice No. 24 (for VDT lighting).
Three quality issues are addressed in this section.
A bright object alone does not necessarily cause glare, but a bright object in front of a dark background, however, usually will cause glare. Contrast is the relationship between the luminance of an object and its background. Although the visual task generally becomes easier with increased contrast, too much contrast causes glare and makes the visual task much more difficult.
You can reduce glare or luminance ratios by not exceeding suggested light levels and by using lighting equipment designed to reduce glare. A louver or lens is commonly used to block direct viewing of a light source. Indirect lighting, or uplighting, can create a low glare environment by uniformly lighting the ceiling. Also, proper fixture placement can reduce reflected glare on work surfaces or computer screens. Standard data now provided with luminaire specifications include tables of its visual comfort probability (VCP) ratings for various room geometries. The VCP index provides an indication of the percentage of people in a given space that would find the glare from a fixture to be acceptable. A minimum VCP of 70 is recommended for commercial interiors, while luminaires with VCPs exceeding 80 are recommended in computer areas.
A scale of 0 to 100 defines the CRI. A higher CRI means better color rendering, or less color shift. CRIs in the range of 75-100 are considered excellent, while 65-75 are good. The range of 55-65 is fair, and 0-55 is poor. Under higher CRI sources, surface colors appear brighter, improving the aesthetics of the space. Sometimes, higher CRI sources create the illusion of higher illuminance levels.
The CRI values for selected light sources are tabulated with other lamp data in Exhibit 3.
Back to the Table of Contents
Color temperature refers to the color of a blackbody radiator at a given absolute temperature, expressed in Kelvins. A blackbody radiator changes color as its temperature increases ( first to red, then to orange, yellow, and finally bluish white at the highest temperature. A "warm" color light source actually has a lower color temperature. For example, a cool-white fluorescent lamp appears bluish in color with a color temperature of around 4100 K. A warmer fluorescent lamp appears more yellowish with a color temperature around 3000 K. Refer to Exhibit 5 for color temperatures of various light sources.
The CRI number does not indicate which colors will shift or by how much; it is rather an indication of the average shift of eight standard colors. Two different light sources may have identical CRI values, but colors may appear quite different under these two sources.
Light is produced by passing a current through a tungsten filament, causing it to become hot and glow. With use, the tungsten slowly evaporates, eventually causing the filament to break.
These lamps are available in many shapes and finishes. The two most common types of shapes are the common "A-type" lamp and the reflector-shaped lamps.
Because the filament is relatively small, this source is often used where a highly focused beam is desired. Compact halogen lamps are popular in retail applications for display and accent lighting. In addition, tungsten-halogen lamps generally produce a whiter light than other incandescent lamps, are more efficient, last longer, and have improved lamp lumen depreciation.
Fluorescent lamps are available in color temperatures ranging from warm (2700(K) "incandescent-like" colors to very cool (6500(K) "daylight" colors. "Cool white" (4100(K) is the most common fluorescent lamp color. Neutral white (3500(K) is becoming popular for office and retail use.
Improvements in the phosphor coating of fluorescent lamps have improved color rendering and made some fluorescent lamps acceptable in many applications previously dominated by incandescent lamps.
As you can see, the optimum operating temperature for the F32T8 lamp-ballast system is higher than for the F40T12 system. Thus, when the ambient temperature is greater than 25C (77F), the performance of the F32T8 system may be higher than the performance under ANSI conditions. Lamps with smaller diameters (such as T-5 twin tube lamps) peak at even higher ambient temperatures.
Manufactured since the early 1980s, they are a long-lasting, energy-efficient substitute for the incandescent lamp.
Various wattages, color temperatures, and sizes are available. The wattages of the compact fluorescents range from 5 to 40 ( replacing incandescent lamps ranging from 25 to 150 watts ( and provide energy savings of 60 to 75 percent. While producing light similar in color to incandescent sources, the life expectancy of a compact fluorescent is about 10 times that of a standard incandescent lamp. Note, however, that the use of compact fluorescent lamps is very limited in dimming applications.
The compact fluorescent lamp with an Edison screw-base offers an easy means to upgrade an incandescent luminaire. Screw-in compact fluorescents are available in two types:
Originally developed for outdoor and industrial applications, HID lamps are also used in office, retail, and other indoor applications. Their color rendering characteristics have been improved and lower wattages have recently become available ( as low as 18 watts.
There are several advantages to HID sources:
The following HID sources are listed in increasing order of efficacy:
The arc is contained in an inner bulb called the arc tube. The arc tube is filled with high purity mercury and argon gas. The arc tube is enclosed within the outer bulb, which is filled with nitrogen.
Color-improved mercury lamps use a phosphor coating on the inner wall of the bulb to improve the color rendering index, resulting in slight reductions in efficiency.
Wattages range from 32 to 2,000, offering a wide range of indoor and outdoor applications. The efficacy of metal halide lamps ranges from 50 to 115 lumens per watt ( typically about double that of mercury vapor. In short, metal halide lamps have several advantages.
The efficacy of the lamp is very high ( as much as 140 lumens per watt. For example, a 400-watt high pressure sodium lamp produces 50,000 initial lumens. The same wattage metal halide lamp produces 40,000 initial lumens, and the 400-watt mercury vapor lamp produces only 21,000 initially.
Sodium, the major element used, produces the "golden" color that is characteristic of HPS lamps. Although HPS lamps are not generally recommended for applications where color rendering is critical, HPS color rendering properties are being improved. Some HPS lamps are now 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 lamps (lumens per watt of low-wattage metal halide is 75-85, while white HPS is 50-60 LPW).
LPS lamp use has been generally limited to outdoor applications such as security or street lighting and indoor, low-wattage applications where color quality is not important (e.g. stairwells). However, because the color rendition is so poor, many municipalities do not allow them for roadway lighting.
Because the LPS lamps are "extended" (like fluorescent), they are less effective in directing and controlling a light beam, compared with "point sources" like high-pressure sodium and metal halide. Therefore, lower mounting heights will provide better results with LPS lamps. To compare a LPS installation with other alternatives, calculate the installation efficacy as the average maintained footcandles divided by the input watts per square foot of illuminated area. The input wattage of an LPS system increases over time to maintain consistent light output over the lamp life.
The low-pressure sodium lamp can explode if the sodium comes in contact with water. Dispose of these lamps according to the manufacturer's instructions.
Back to the Table of Contents
"Cathode cut-out" (or "hybrid") ballasts are high-efficiency core-coil ballasts that incorporate electronic components that cut off power to the lamp cathodes (filaments) after the lamps are lit, resulting in an additional 2-watt savings per standard lamp. Also, many partial-output T12 hybrid ballasts provide up to 10% less light output while consuming up to 17% less energy than energy-efficient magnetic ballasts. Full-output T8 hybrid ballasts are nearly as efficient as rapid-start two-lamp T8 electronic ballasts.
There are three electronic ballast designs available:
Standard T12 electronic ballasts (430 mA)
These ballasts are designed for use with conventional (T12 or T10) fluorescent lighting systems. Some electronic ballasts that are designed for use with 4' lamps can operate up to four lamps at a time. Parallel wiring is another feature now available that allows all companion lamps in the ballast circuit to continue operating in the event of a lamp failure. Electronic ballasts are also available for 8' standard and high-output T12 lamps.
T8 Electronic ballasts (265 mA)
Specifically designed for use with T8 (1-inch diameter) lamps, the T8 electronic ballast provides the highest efficiency of any fluorescent lighting system. Some T8 electronic ballasts are designed to start the lamps in the conventional rapid start mode, while others are operated in the instant start mode. The use of instant start T8 electronic ballasts may result in up to 25 percent reduction in lamp life (at 3 hours per start) but produces slight increases in efficiency and light output. (Note: Lamp life ratings for instant start and rapid start are the same for 12 or more hours per start.)
Dimmable electronic ballasts
These ballasts permit the light output of the lamps to be dimmed based on input from manual dimmer controls or from devices that sense daylight or occupancy.
The rapid start circuit is the most used system today. Rapid start ballasts provide continuous lamp filament heating during lamp operation (except when used with a cathode cut-out ballast or lamp). Users notice a very short delay after "flipping the switch," before the lamp is started.
The instant start system ignites the arc within the lamp instantly. This ballast provides a higher starting voltage, which eliminates the need for a separate starting circuit. This higher starting voltage causes more wear on the filaments, resulting in reduced lamp life compared with rapid starting.
The preheat circuit was used when fluorescent lamps first became available. This technology is used very little today, except for low-wattage magnetic ballast applications such as compact fluorescents. A separate starting switch, called a starter, is used to aid in forming the arc. The filament needs some time to reach proper temperature, so the lamp does not strike for a few seconds.
With HID ballasts, a major performance consideration is lamp wattage regulation when the line voltage varies. With HPS lamps, the ballast must compensate for changes in the lamp voltage as well as for changes in the line voltages.
Installing the wrong HID ballast can cause a variety of problems:
Electronic ballasts for some types of HID lamps are starting to become commercially available. These ballasts offer the advantages of reduced size and weight, as well as better color control; however, electronic HID ballasts offer minimal efficiency gains over magnetic HID ballasts.
Back to the Table of Contents
The main function of the luminaire is to direct light using reflective and shielding materials. Many lighting upgrade projects consist of replacing one or more of these components to improve fixture efficiency. Alternatively, users may consider replacing the entire luminaire with one that I designed to efficiently provide the appropriate quantity and quality of illumination.
There are several different types of luminaires. The following is a listing of some of the common luminaire types:
Surface deterioration and accumulated dirt in older, poorly maintained fixtures can also cause reductions in luminaire efficiency. Refer to Lighting Maintenance for more information.
In most incandescent spot and flood lights, highly specular (mirror-like) reflectors are usually built into the lamps.
One energy-efficient upgrade option is to install a custom-designed reflector to enhance the light control and efficiency of the fixture, which may allow partial delamping. Retrofit reflectors are useful for upgrading the efficiency of older, deteriorated luminaire surfaces. A variety of reflector materials are available: highly reflective white paint, silver film laminate, and two grades of anodized aluminum sheet (standard or enhanced reflectivity). Silver film laminate is generally considered to have the highest reflectance, but is considered less durable.
Proper design and installation of reflectors can have more effect on performance than the reflector materials. In combination with delamping, however, the use of reflectors may result in reduced light output and may redistribute the light, which may or may not be acceptable for a specific space or application. To ensure acceptable performance from reflectors, arrange for a trial installation and measure "before" and "after" light levels using the procedures outlined in Lighting Evaluations. For specific name-brand performance data, refer to Specifier Reports, "Specular Reflectors," Volume 1, Issue 3, National Lighting Product Information Program.
Lenses. Lenses made from clear ultraviolet-stabilized acrylic plastic deliver the most light output and uniformity of all shielding media. However, they provide less glare control than louvered fixtures. Clear lens types include prismatic, batwing, linear batwing, and polarized lenses. Lenses are usually much less expensive than louvers. White translucent diffusers are much less efficient than clear lenses, and they result in relatively low visual comfort probability. New low-glare lens materials are available for retrofit and provide high visual comfort (VCP>80) and high efficiency.
Louvers. Louvers provide superior glare control and high visual comfort compared with lens-diffuser systems. The most common application of louvers is to eliminate the fixture glare reflected on computer screens. So-called "deep-cell" parabolic louvers ( with 5-7" cell apertures and depths of 2-4" ( provide a good balance between visual comfort and luminaire efficiency. Although small-cell parabolic louvers provide the highest level of visual comfort, they reduce luminaire efficiency to about 35-45 percent. For retrofit applications, both deep-cell and small-cell louvers are available for use with existing fixtures. Note that the deep-cell louver retrofit adds 2-4" to the overall depth of a troffer; verify that sufficient plenum depth is available before specifying the deep-cell retrofit.
The lighting upgrade products mentioned in this document are described in more detail in Lighting Upgrade Technologies.
Back to the Table of Contents
EPRI, the CEC, and the DOE have collaborated to produce the 1993 update of the Advanced Lighting Guidelines (originally published in 1990 by the CEC). The Guidelines include four new chapters that address lighting controls. This series of guidelines provides comprehensive and objective information about current lighting equipment and controls.
The Guidelines address the following areas:
To obtain a copy of the Advanced Lighting Guidelines (1993), contact your local utility (if your utility is a member of EPRI). Otherwise, call the CEC at (916) 654-5200.
The Association of Energy Engineers uses this text to prepare applicants to take the Certified Lighting Efficiency Professional (CLEP) examination. This 480-page book is particularly useful for learning about illuminance calculations, basic design considerations, and the operating characteristics of each light source family. It also provides application guidelines for industrial, office, retail, and outdoor lighting.
You can order this textbook from the Association of Energy Engineers by calling (404) 925-9558.
ASHRAE/IES Standard 90.1-1989, American Society of Heating Refrigerating and Air-Conditioning Engineers (ASHRAE) and Illuminating Engineering Society (IES), 1989.
Commonly known as "Standard 90.1," ASHRAE/IES 90.1-1989 is the efficiency standard that Green Lights participants agree to follow when designing new lighting systems. Standard 90.1 is currently a national, voluntary consensus standard. However, this standard is becoming law in many states. The Energy Policy Act of 1992 requires that all states certify by October 1994 that their commercial energy code provisions meet or exceed the requirements Standard 90.1.
Green Lights participants only need to meet the lighting system portion of the standard. Standard 90.1 sets maximum wattage densities (W/SF) for lighting systems based on the type of building or expected uses within each space. The lighting portion of Standard 90.1 does not apply to the following: outdoor manufacturing or processing facilities, theatrical lighting, specialty lighting, emergency lighting, signage, retail display windows, and dwelling unit lighting. Daylighting and lighting controls receive consideration and credits, and minimum efficiency standards are specified for fluorescent lamp ballasts based on the Federal Ballast Standards.
You can purchase Standard 90.1 by contacting ASHRAE at (404) 636-8400 or IES at (212) 248-5000.
Lighting Management Handbook, Craig DiLouie, 1993.
This 300-page non-technical reference provides a clear overview of lighting management principles. It places special emphasis on the importance of effective maintenance and the benefits of a well planned and executed lighting management program. The contents are organized as follows:
Illuminations: A Training Textbook for Senior Lighting Technicians, interNational Association of Lighting Management Companies (NALMCO), First Edition, 1993.
Illuminations is a 74-page course workbook for use by Apprentice Lighting Technicians (NALMCO designation) for upgrading their status to Senior Lighting Technician. The workbook consists of seven chapters, each with a quiz for self-testing. Answers are provided in the back of the book.
To order, call the NALMCO at (609) 799-5501.
The Commercial Lighting Efficiency Resource Book provides an overview of efficient commercial lighting technologies and programs available to the end-user. Besides providing an overview of lighting conservation opportunities, this 144-page document provides valuable information about lighting education and information in the following areas:
The following lighting publications are available from EPRI. Each publication contains a thorough description of the technologies, their advantages, their applications, and case studies.
To obtain a copy of EPRI Lighting Publications, contact your local utility (if your utility is a member of EPRI). Otherwise, contact the EPRI Publications Distribution Center at (510) 934-4212.
Lighting Fundamentals Handbook, Electric Power Research Institute, TR-101710, March 1993.
This handbook provides basic information on lighting principles, lighting equipment, and other considerations related to lighting design. It is not intended to be an up-to-date reference on current lighting products and equipment. The handbook has three major sections:
The Handbook is an essential reference for the practicing lighting engineer. You can purchase the manual from the publications office of IES at (212) 248-5000. IES members receive a price discount on the Handbook.
You can purchase the 168-page reference from the publications office of IES at (212) 248-5000. IES members receive the Ready Reference upon joining the society.
To purchase a copy of RP-24, contact the IES at (212) 248-5000.
The following publications are basic references that provide an overview of the subject and include lighting applications.
To order, call NLB at (202) 457-8437.
To purchase these publications, fax your request to the Lighting Research Center, Rensselaer Polytechnic Institute at (518) 276-2999 (fax).
This monthly publication addresses many aspects of the energy industry. Each edition contains a section devoted to lighting, usually featuring a case study and at least one article discussing a lighting product or issue. Some Energy User News issues feature product guides, which are technology-specific tables that list the participating manufacturers (with phone numbers) and the attributes of their products. The September 1993 edition featured lighting as the centerpiece, and contained the following information.
To order a subscription, call NALMCO at (609) 799-5501.
To receive a free subscription to the Update, contact Green Lights Customer Service at (202) 775-6650 or fax (202) 775-6680.
These documents are available through the Green Lights faxline. To request fax delivery, call the faxline at (202) 233-9659. Periodically contact the faxline to retrieve the latest information from Green Lights. If you do not have a fax machine, contact Green Lights Customer Service at (202) 775-6650.
For additional information, please contact Green Lights Customer Service at (202) 775-6650 or fax (202) 775-6680.
To order copies of the brochure, please contact Green Lights Customer Service at (202) 775-6650 or fax (202) 775-6680
Back to the Table of Contents
ANSI: Abbreviation for American National Standards Institute.
ARC TUBE: A tube enclosed by the outer glass envelope of a HID lamp and made of clear quartz or ceramic that contains the arc stream.
ASHRAE: American Society of Heating, Refrigerating and Air-Conditioning Engineers
BAFFLE: A single opaque or translucent element used to control light distribution at certain angles.
BALLAST: A device used to operate fluorescent and HID lamps. The ballast provides the necessary starting voltage, while limiting and regulating the lamp current during operation.
BALLAST CYCLING: Undesirable condition under which the ballast turns lamps on and off (cycles) due to the overheating of the thermal switch inside the ballast. This may be due to incorrect lamps, improper voltage being supplied, high ambient temperature around the fixture, or the early stage of ballast failure.
BALLAST EFFICIENCY FACTOR: The ballast efficiency factor (BEF) is the ballast factor (see below) divided by the input power of the ballast. The higher the BEF ( within the same lamp-ballast type ( the more efficient the ballast.
BALLAST FACTOR: The ballast factor (BF) for a specific lamp-ballast combination represents the percentage of the rated lamp lumens that will be produced by the combination.
CANDELA: Unit of luminous intensity, describing the intensity of a light source in a specific direction.
CANDELA DISTRIBUTION: A curve, often on polar coordinates, illustrating the variation of luminous intensity of a lamp or luminaire in a plane through the light center.
CANDLEPOWER: A measure of luminous intensity of a light source in a specific direction, measured in candelas (see above).
CBM: Abbreviation for Certified Ballast Manufacturers Association.
CEC: Abbreviation for California Energy Commission.
COEFFICIENT OF UTILIZATION: The ratio of lumens from a luminaire received on the work plane to the lumens produced by the lamps alone. (Also called "CU")
COLOR RENDERING INDEX (CRI): A scale of the effect of a light source on the color appearance of an object compared to its color appearance under a reference light source. Expressed on a scale of 1 to 100, where 100 indicates no color shift. A low CRI rating suggests that the colors of objects will appear unnatural under that particular light source.
COLOR TEMPERATURE: The color temperature is a specification of the color appearance of a light source, relating the color to a reference source heated to a particular temperature, measured by the thermal unit Kelvin. The measurement can also be described as the "warmth" or "coolness" of a light source. Generally, sources below 3200K are considered "warm;" while those above 4000K are considered "cool" sources.
COMPACT FLUORESCENT: A small fluorescent lamp that is often used as an alternative to incandescent lighting. The lamp life is about 10 times longer than incandescent lamps and is 3-4 times more efficacious. Also called PL, Twin-Tube, CFL, or BIAX lamps.
CONSTANT WATTAGE (CW) BALLAST: A premium type of HID ballast in which the primary and secondary coils are isolated. It is considered a high performance, high loss ballast featuring excellent output regulation.
CONSTANT WATTAGE AUTOTRANSFORMER (CWA) BALLAST: A popular type of HID ballast in which the primary and secondary coils are electrically connected. Considered an appropriate balance between cost and performance.
CONTRAST: The relationship between the luminance of an object and its background.
CRI: (SEE COLOR RENDERING INDEX)
CUT-OFF ANGLE: The angle from a fixture's vertical axis at which a reflector, louver, or other shielding device cuts off direct visibility of a lamp. It is the complementary angle of the shielding angle.
DAYLIGHT COMPENSATION: A dimming system controlled by a photocell that reduces the output of the lamps when daylight is present. As daylight levels increase, lamp intensity decreases. An energy-saving technique used in areas with significant daylight contribution.
DIFFUSE: Term describing dispersed light distribution. Refers to the scattering or softening of light.
DIFFUSER: A translucent piece of glass or plastic sheet that shields the light source in a fixture. The light transmitted throughout the diffuser will be redirected and scattered.
DIRECT GLARE: Glare produced by a direct view of light sources. Often the result of insufficiently shielded light sources. (See GLARE)
DOWNLIGHT: A type of ceiling luminaire, usually fully recessed, where most of the light is directed downward. May feature an open reflector and/or shielding device.
EFFICACY: A metric used to compare light output to energy consumption. Efficacy is measured in lumens per watt. Efficacy is similar to efficiency, but is expressed in dissimilar units. For example, if a 100-watt source produces 9000 lumens, then the efficacy is 90 lumens per watt.
ELECTROLUMINESCENT: A light source technology used in exit signs that provides uniform brightness, long lamp life (approximately eight years), while consuming very little energy (less than one watt per lamp).
ELECTRONIC BALLAST: A ballast that uses semi-conductor components to increase the frequency of fluorescent lamp operation ( typically in the 20-40 kHz range. Smaller inductive components provide the lamp current control. Fluorescent system efficiency is increased due to high frequency lamp operation.
ELECTRONIC DIMMING BALLAST: A variable output electronic fluorescent ballast.
EMI: Abbreviation for electromagnetic interference. High frequency interference (electrical noise) caused by electronic components or fluorescent lamps that interferes with the operation of electrical equipment. EMI is measured in micro-volts, and can be controlled by filters. Because EMI can interfere with communication devices, the Federal Communication Commission (FCC) has established limits for EMI.
ENERGY-SAVING BALLAST: A type of magnetic ballast designed so that the components operate more efficiently, cooler and longer than a "standard magnetic" ballast. By US law, standard magnetic ballasts can no longer be manufactured.
ENERGY-SAVING LAMP: A lower wattage lamp, generally producing fewer lumens.
FC: (SEE FOOTCANDLE)
FLUORESCENT LAMP: A light source consisting of a tube filled with argon, along with krypton or other inert gas. When electrical current is applied, the resulting arc emits ultraviolet radiation that excites the phosphors inside the lamp wall, causing them to radiate visible light.
FOOTCANDLE (FC): The English unit of measurement of the illuminance (or light level) on a surface. One footcandle is equal to one lumen per square foot.
FOOTLAMBERT: English unit of luminance. One footlambert is equal to 1/p candelas per square foot.
GLARE: The effect of brightness or differences in brightness within the visual field sufficiently high to cause annoyance, discomfort or loss of visual performance.
HALOGEN: (SEE TUNGSTEN HALOGEN LAMP)
HARMONIC DISTORTION: A harmonic is a sinusoidal component of a periodic wave having a frequency that is a multiple of the fundamental frequency. Harmonic distortion from lighting equipment can interfere with other appliances and the operation of electric power networks. The total harmonic distortion (THD) is usually expressed as a percentage of the fundamental line current. THD for 4-foot fluorescent ballasts usually range from 20% to 40%. For compact fluorescent ballasts, THD levels greater than 50% are not uncommon.
HID: Abbreviation for high intensity discharge. Generic term describing mercury vapor, metal halide, high pressure sodium, and (informally) low pressure sodium light sources and luminaires.
HIGH-BAY: Pertains to the type of lighting in an industrial application where the ceiling is 20 feet or higher. Also describes the application itself.
HIGH OUTPUT (HO): A lamp or ballast designed to operate at higher currents (800 mA) and produce more light.
HIGH POWER FACTOR: A ballast with a 0.9 or higher rated power factor, which is achieved by using a capacitor.
HIGH PRESSURE SODIUM LAMP: A high intensity discharge (HID) lamp whose light is produced by radiation from sodium vapor (and mercury).
HOT RESTART or HOT RESTRIKE: The phenomenon of re-striking the arc in an HID light source after a momentary power loss. Hot restart occurs when the arc tube has cooled a sufficient amount.
IESNA: Abbreviation for Illuminating Engineering Society of North America.
ILLUMINANCE: A photometric term that quantifies light incident on a surface or plane. Illuminance is commonly called light level. It is expressed as lumens per square foot (footcandles), or lumens per square meter (lux).
INDIRECT GLARE: Glare produced from a reflective surface.
INSTANT START: A fluorescent circuit that ignites the lamp instantly with a very high starting voltage from the ballast. Instant start lamps have single-pin bases.
LAMP CURRENT CREST FACTOR (LCCF): The peak lamp current divided by the RMS (average) lamp current. Lamp manufacturers require <1.7 for best lamp life. An LCCF of 1.414 is a perfect sine wave.
LAMP LUMEN DEPRECIATION FACTOR (LLD): A factor that represents the reduction of lumen output over time. The factor is commonly used as a multiplier to the initial lumen rating in illuminance calculations, which compensates for the lumen depreciation. The LLD factor is a dimensionless value between 0 and 1.
LAY-IN-TROFFER: A fluorescent fixture; usually a 2' x 4' fixture that sets or "lays" into a specific ceiling grid.
LED: Abbreviation for light emitting diode. An illumination technology used for exit signs. Consumes low wattage and has a rated life of greater than 80 years.
LENS: Transparent or translucent medium that alters the directional characteristics of light passing through it. Usually made of glass or acrylic.
LIGHT LOSS FACTOR (LLF): Factors that allow for a lighting system's operation at less than initial conditions. These factors are used to calculate maintained light levels. LLFs are divided into two categories, recoverable and non-recoverable. Examples are lamp lumen depreciation and luminaire surface depreciation.
LIFE-CYCLE COST: The total costs associated with purchasing, operating, and maintaining a system over the life of that system.
LOUVER: Grid type of optical assembly used to control light distribution from a fixture. Can range from small-cell plastic to the large-cell anodized aluminum louvers used in parabolic fluorescent fixtures.
LOW POWER FACTOR: Essentially, an uncorrected ballast power factor of less than 0.9 (SEE NPF)
LOW-PRESSURE SODIUM: A low-pressure discharge lamp in which light is produced by radiation from sodium vapor. Considered a monochromatic light source (most colors are rendered as gray).
LOW-VOLTAGE LAMP: A lamp ( typically compact halogen ( that provides both intensity and good color rendition. Lamp operates at 12V and requires the use of a transformer. Popular lamps are MR11, MR16, and PAR36.
LOW-VOLTAGE SWITCH: A relay (magnetically-operated switch) that allows local and remote control of lights, including centralized time clock or computer control.
LUMEN: A unit of light flow, or luminous flux. The lumen rating of a lamp is a measure of the total light output of the lamp.
LUMINAIRE: A complete lighting unit consisting of a lamp or lamps, along with the parts designed to distribute the light, hold the lamps, and connect the lamps to a power source. Also called a fixture.
LUMINAIRE EFFICIENCY: The ratio of total lumen output of a luminaire and the lumen output of the lamps, expressed as a percentage. For example, if two luminaires use the same lamps, more light will be emitted from the fixture with the higher efficiency.
LUMINANCE: A photometric term that quantifies brightness of a light source or of an illuminated surface that reflects light. It is expressed as footlamberts (English units) or candelas per square meter (Metric units).
LUX (LX): The metric unit of measure for illuminance of a surface. One lux is equal to one lumen per square meter. One lux equals 0.093 footcandles.
MAINTAINED ILLUMINANCE: Refers to light levels of a space at other than initial or rated conditions. This terms considers light loss factors such as lamp lumen depreciation, luminaire dirt depreciation, and room surface dirt depreciation.
MERCURY VAPOR LAMP: A type of high intensity discharge (HID) lamp in which most of the light is produced by radiation from mercury vapor. Emits a blue-green cast of light. Available in clear and phosphor-coated lamps.
METAL HALIDE: A type of high intensity discharge (HID) lamp in which most of the light is produced by radiation of metal halide and mercury vapors in the arc tube. Available in clear and phosphor-coated lamps.
MR-16: A low-voltage quartz reflector lamp, only 2" in diameter. Typically the lamp and reflector are one unit, which directs a sharp, precise beam of light.
NADIR: A reference direction directly below a luminaire, or "straight down" (0 degree angle).
NEMA: Abbreviation for National Electrical Manufacturers Association.
NIST: Abbreviation for National Institute of Standards and Technology.
NPF (NORMAL POWER FACTOR): A ballast/lamp combination in which no components (e.g., capacitors) have been added to correct the power factor, making it normal (essentially low, typically 0.5 or 50%).
OCCUPANCY SENSOR: Control device that turns lights off after the space becomes unoccupied. May be ultrasonic, infrared or other type.
OPTICS: A term referring to the components of a light fixture (such as reflectors, refractors, lenses, louvers) or to the light emitting or light-controlling performance of a fixture.
PAR LAMP: A parabolic aluminized reflector lamp. An incandescent, metal halide, or compact fluorescent lamp used to redirect light from the source using a parabolic reflector. Lamps are available with flood or spot distributions.
PAR 36: A PAR lamp that is 36 one-eighths of an inch in diameter with a parabolic shaped reflector (SEE PAR LAMP).
PARABOLIC LUMINAIRE: A popular type of fluorescent fixture that has a louver composed of aluminum baffles curved in a parabolic shape. The resultant light distribution produced by this shape provides reduced glare, better light control, and is considered to have greater aesthetic appeal.
PARACUBE: A metallic coated plastic louver made up of small squares. Often used to replace the lens in an installed troffer to enhance its appearance. The paracube is visually comfortable, but the luminaire efficiency is lowered. Also used in rooms with computer screens because of their glare-reducing qualities.
PHOTOCELL: A light sensing device used to control luminaires and dimmers in response to detected light levels.
PHOTOMETRIC REPORT: A photometric report is a set of printed data describing the light distribution, efficiency, and zonal lumen output of a luminaire. This report is generated from laboratory testing.
POWER FACTOR: The ratio of AC volts x amps through a device to AC wattage of the device. A device such as a ballast that measures 120 volts, 1 amp, and 60 watts has a power factor of 50% (volts x amps = 120 VA, therefore 60 watts/120 VA = 0.5). Some utilities charge customers for low power factor systems.
PREHEAT: A type of ballast/lamp circuit that uses a separate starter to heat up a fluorescent lamp before high voltage is applied to start the lamp.
QUAD-TUBE LAMP: A compact fluorescent lamp with a double twin tube configuration.
RADIO FREQUENCY INTERFERENCE (RFI): Interference to the radio frequency band caused by other high frequency equipment or devices in the immediate area. Fluorescent lighting systems generate RFI.
RAPID START (RS): The most popular fluorescent lamp/ballast combination used today. This ballast quickly and efficiently preheats lamp cathodes to start the lamp. Uses a "bi-pin" base.
ROOM CAVITY RATIO (RCR): A ratio of room dimensions used to quantify how light will interact with room surfaces. A factor used in illuminance calculations.
REFLECTANCE: The ratio of light reflected from a surface to the light incident on the surface. Reflectances are often used for lighting calculations. The reflectance of a dark carpet is around 20%, and a clean white wall is roughly 50% to 60%.
REFLECTOR: The part of a light fixture that shrouds the lamps and redirects some light emitted from the lamp.
REFRACTOR: A device used to redirect the light output from a source, primarily by bending the waves of light.
RECESSED: The term used to describe the doorframe of a troffer where the lens or louver lies above the surface of the ceiling.
REGULATION: The ability of a ballast to hold constant (or nearly constant) the output watts (light output) during fluctuations in the voltage feeding of the ballast. Normally specified as +/- percent change in output compared to +/- percent change in input.
RELAY: A device that switches an electrical load on or off based on small changes in current or voltage. Examples: low voltage relay and solid state relay.
RETROFIT: Refers to upgrading a fixture, room, or building by installing new parts or equipment.
SELF-LUMINOUS EXIT SIGN: An illumination technology using phosphor-coated glass tubes filled with radioactive tritium gas. The exit sign uses no electricity and thus does not need to be hardwired.
SEMI-SPECULAR: Term describing the light reflection characteristics of a material. Some light is reflected directionally, with some amount of scatter.
SHIELDING ANGLE: The angle measured from the ceiling plane to the line of sight where the bare lamp in a luminaire becomes visible. Higher shielding angles reduce direct glare. It is the complementary angle of the cutoff angle. (See CUTOFF ANGLE).
SPACING CRITERION: A maximum distance that interior fixtures may be spaced that ensures uniform illumination on the work plane. The luminaire height above the work plane multiplied by the spacing criterion equals the center-to-center luminaire spacing.
SPECULAR: Mirrored or polished surface. The angle of reflection is equal to the angle of incidence. This word describes the finish of the material used in some louvers and reflectors.
STARTER: A device used with a ballast to start preheat fluorescent lamps.
STROBOSCOPIC EFFECT: Condition where rotating machinery or other rapidly moving objects appear to be standing still due to the alternating current supplied to light sources. Sometimes called "strobe effect."
T12 LAMP: Industry standard for a fluorescent lamp that is 12 one-eighths (1 inches) in diameter. Other sizes are T10 (1 inches) and T8 (1 inch) lamps.
TANDEM WIRING: A wiring option in which a ballasts is shared by two or more luminaires. This reduces labor, materials, and energy costs. Also called "master-slave" wiring.
THERMAL FACTOR: A factor used in lighting calculations that compensates for the change in light output of a fluorescent lamp due to a change in bulb wall temperature. It is applied when the lamp-ballast combination under consideration is different from that used in the photometric tests.
TRIGGER START: Type of ballast commonly used with 15-watt and 20-watt straight fluorescent lamps.
TROFFER: The term used to refer to a recessed fluorescent light fixture (combination of trough and coffer).
TUNGSTEN HALOGEN LAMP: A gas-filled tungsten filament incandescent lamp with a lamp envelope made of quartz to withstand the high temperature. This lamp contains some halogens (namely iodine, chlorine, bromine, and fluorine), which slow the evaporation of the tungsten. Also, commonly called a quartz lamp.
TWIN-TUBE: (SEE COMPACT FLUORESCENT LAMP)
ULTRA VIOLET (UV): Invisible radiation that is shorter in wavelength and higher in frequency than visible violet light (literally beyond the violet light).
UNDERWRITERS' LABORATORIES (UL): An independent organization whose responsibilities include rigorous testing of electrical products. When products pass these tests, they can be labeled (and advertised) as "UL listed." UL tests for product safety only.
VANDAL-RESISTANT: Fixtures with rugged housings, break-resistant type shielding, and tamper-proof screws.
VCP: Abbreviation for visual comfort probability. A rating system for evaluating direct discomfort glare. This method is a subjective evaluation of visual comfort expressed as the percent of occupants of a space who will be bothered by direct glare. VCP allows for several factors: luminaire luminances at different angles of view, luminaire size, room size, luminaire mounting height, illuminance, and room surface reflectivity. VCP tables are often provided as part of photometric reports.
VERY HIGH OUTPUT (VHO): A fluorescent lamp that operates at a "very high" current (1500 mA), producing more light output than a "high output" lamp (800 mA) or standard output lamp (430 mA).
VOLT: The standard unit of measurement for electrical potential. It defines the "force" or "pressure" of electricity.
VOLTAGE: The difference in electrical potential between two points of an electrical circuit.
WALLWASHER: Describes luminaires that illuminate vertical surfaces.
WATT (W): The unit for measuring electrical power. It defines the rate of energy consumption by an electrical device when it is in operation. The energy cost of operating an electrical device is calculated as its wattage times the hours of use. In single phase circuits, it is related to volts and amps by the formula: Volts x Amps x PF = Watts. (Note: For AC circuits, PF must be included.)
WORK PLANE: The level at which work is done and at which illuminance is specified and measured. For office applications, this is typically a horizontal plane 30 inches above the floor (desk height).
ZENITH: The direction directly above the luminaire (180( angle).
Green Lights Program
401 M Street, SW (6202J)
Washington, DC 20460
or call the Green Lights Information Hotline at (202)
775-6650, Fax (202) 775-6680. Look in the monthly Green Lights &
Energy Star Update newsletter for announcements of new publications.