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Energy Efficient Lighting
    Lighting Glossary

# | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z
 #  
l6Ga Galvanized Steel
A steel commonly used in internal or unseen functional parts of a fixture. This metal is used because it doesn’t require finishing or painting. Steel is galvanized by applying a layer of zinc to the raw metal sheets. This process helps preserve the material and prevent it from rusting. About 0.060 in. thickness.
2OGa CRS 20-Gauge Cold Rolled Steel
The most common type of steel used in the lighting industry. Cold rolling indicates that the steel is not heat-treated or hardened, which allows easy forming and piercing in the making of a lighting fixture. About 0.036 in. in thickness.
120V 60Hz AC
120-Volt Alternating Current is the standard voltage used in many of the residential and light commercial buildings in the United States. Most lighting fixtures and ballasts are designed to run on at this voltage level. Hertz (Hz), or cycles per second, is a unit of frequency of electric current. 60 Hertz is the common U.S. rating.
277V 60Hz AC
277-Volt Alternating Current is a common voltage standard used in many commercial fixture applications in the United States. The higher voltage makes it easier to wire many fixtures together on fewer circuits, making installations easier and simpler. Specially designed ballasts are required for operation at this voltag
   A
A-Lamps
(General Service Bulbs) The standard incandescent bulb for most common uses.
Alzak Reflector
A Clear Specular Reflector is a proprietary anodizing process that allows maximum light reflection from the reflective surface with low brightness and glare. Alzak is a registered trademark, originally of Alcoa.
Amperes
(Amps) A measure of electrical current. In incandescent lamps, the current is related to voltage and power as follows: Current (Amps) = Power (Watts) / Voltage (Volts).
ANSI
American National Standards Institute. A consensus-based organization which coordinates voluntary standards for the physical, electrical and performance characteristics of lamps, ballasts, luminaires and other lighting and electrical equipment.
Anodized Aluminum
Anodizing is one of the most common finishing processes done to aluminum in the lighting industry. Anodizing is a controlled oxidation produced by exposing aluminum to an electrically charged chemical bath. The end result is a hardened surface that resists abrasion and corrosion with an added protective transparent layer to preserve the natural aluminum finish. Anodizing can also produce colored or dyed finishes that are locked into the aluminum surface. Pre-anodizing is usually performed on the raw coil of aluminum before it is fabricated into a louver or reflector.
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
Average rated life
The time expressed in hours that half of a given number of test lamps burnt out in. The life span of individual bulbs purchased will almost always be slightly above or below this time.
AWG
American Wire Gauge used to designate electrical wire size and insulation. Eg., AWG#12 90C is a No. 12 size conductor equal to 0.095 in. diameter with an insulation that can withstand up to a 90°C (194°F) temperature.
AWM/THHN
Appliance Wiring Material (AWM) is common internal fixture wiring. THHN wire is rated at 90°C and can carry up to 600 volts. It is a heavier nylon jacketed wire for use in dry locations and can be used in building wiring connections.
   B
Baffle
A single opaque or translucent element used to control light distribution at certain angles.
Baked White Enamel
A common paint finish that is applied in a "wet" form and applied with a gun or automated sprayer. The paint is usually attracted to the metal part electro-statically to prevent excessive paint over-spray. The paint is finally baked on for maximum adhesion. The final paint thickness is usually 0.7 to 1.1 mm when dry.
Ballast
An auxiliary piece of equipment required to start and to properly control the flow of current to gas discharge light sources such as fluorescent and high intensity discharge (HID) lamps.
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 (BEF)
The ballast efficiency factor 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 (BF)
This is the percentage of a lamp's rated lumen output that can be expected when operated on a specific, commercially available ballast. For example, a ballast with a ballast factor of 0.93 will result in the lamp's emitting 93% of its rated lumen output. A ballast with a lower BF results in less light output and also generally consumes less power.
Bayonet Base
A style of bulb base which uses keyways instead of threads to connect the bulb to the fixture base. The bulb is locked in place by pushing it down and turning it clockwise.
Base of socket
The socket is the receptacle connected to the electrical supply; the base is the end of the lamp that fits into the socket. There are many types of bases used in lamps, screw bases being the most common for incandescent and HID lamps, while bi-pin bases are common for linear fluorescent lamps. The lamp base mechanically holds the lamp in place in the application. The lamp base directly or indirectly (via a cable or lead-in wires) conducts electricity from the circuit to the lamp and can be designed to dissipate heat. Lamp bases should be operated within specified temperature range.
Beam Angle
The angular dimension of the cone of light from reflectorized lamps (such as R and PAR types) encompassing the central part of the beam out to the angle where the intensity is 50% of maximum. The beam angle sometimes called "beam spread" is often part of the ordering code for the reflectorized lamps. Example: The 50PAR30/HIR/NFL25 is a 50 watt PAR30 narrow flood lamp with a beam angle of 25 degrees. See also Field Angle.
Bi-Pin
This is the typical base for a fluorescent tube of 1 to 4 feet in length. It consists of 2 prong contacts which connect into the fixture. Medium bi-pins are used with type T-8 and T-12 tubular fluorescent lamps, and miniature bi-pins are used for tubular T-5 fluorescent lamps.
Bulb
The everyday term for an incandescent lamp. Bulb refers to the outer glass bulb containing the light source. The lighting industry technical term is lamp.
Bulb Size and Shape
Bulbs or lamps are marked with the shape followed by the size. The maximum diameter of the bulb is noted in eighths of an inch. Compact Fluorescent bulbs are "S", "D", "T", or "Q" shapes (denoting single, double, triple and quad sizes.) The code also includes a reference such as T4 to represent the size of the tube.
   C
CBM Certified
Certified Ballast Manufacturers Association certification identifies ballasts that are produced to conform to American National Standard Institute (ANSI) standards.
CSA
Canadian Standards Association. An organization that writes standards and tests lighting equipment for performance as well as electrical and fire safety. Canadian provincial laws generally require that all products sold for consumer use in Canada must have CSA or equivalent approval.
Candela (cd)
The measure of luminous intensity of a source in a given direction. The term has been retained from the early days of lighting when a standard candle of a fixed size and composition was defined as producing one candela in every direction. A plot of intensity versus direction is called a candela distribution curve and is often provided for reflectorized lamps and for luminaires with a lamp operating in them.
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
An obsolete term for luminous intensity; current practice is to refer to this simply as candelas.
CEC
California Energy Commission
Center Beam Candlepower (CBCP)
Refers to the luminous intensity at the center of the beam of a blown or pressed reflector lamp (such as a PAR lamp). Measured in candelas.
Ceramic Metal Halide
A type of metal halide lamp that uses a ceramic material for the arc tube instead of glass quartz, resulting in better color rendering (>80 CRI) and improved lumen maintenance.
Class P-Rated
A standard created by UL indicating an internal thermal protection device that protects against overheating, excessive voltage supply, internal ballast short circuiting, inadequate lamp maintenance and improper fixture application.
Code Gauge
This is a catch-all term used by many people to refer to the gauge of metal used in a fixture -- acceptable to the certain prevailing national electrical or local code requirements for fixture construction.
Coefficient of Utilization (CU)
In general lighting calculations, the fraction of initial lamp lumens that reach the work plane. CU is a function of luminaire efficiency, room surface reflectances and room shape.
Color Rendering Index (CRI)
An international system used to rate a lamp's ability to render object colors. The higher the CRI (based upon a 0-100 scale) the richer colors generally appear. CRI ratings of various lamps may be compared, but a numerical comparison is only valid if the lamps are close in color temperature. CRI differences among lamps are not usually significant (visible to the eye) unless the difference is more than 3-5 points.
Color Temperature (Correlated Color Temperature - CCT)
A number indicating the degree of "yellowness" or "blueness" of a white light source. Measured in kelvins, CCT represents the temperature an incandescent object (like a filament) must reach to mimic the color of the lamp. Yellowish-white ("warm") sources, like incandescent lamps, have lower color temperatures in the 2700K-3000K range; white and bluish-white ("cool") sources, such as cool white (4100K) and natural daylight (6000K), have higher color temperatures. The higher the color temperature the whiter, or bluer, the light will be.
Compact Fluorescent Lamp (CFL)
The general term applied to fluorescent lamps that are single-ended and that have smaller diameter tubes that are bent to form a compact shape. Some CFLs have integral ballasts and medium or candalabra screw bases for easy replacement of incandescent lamps.
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.
Cool White
A general term used to denote a color temperature of around 4100 K. The Cool White (CW) designation is used fluorescent bulbs, LED Lamps, and Induction Lamps.
Correlated Color temperature
(CCT) This specifies the color that a given bulb appears when it is in use. (Whether it looks ‘hot’ ‘warm’ or ‘cold’). It is compared in degrees Kelvin (K), to a source of reference at a given temperature.
CUL
UL certification of testing to Canadian UL standards.
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.
   D
Damp Location/Wet Location
Damp location fixtures can be used in areas where a certain level of humidity is present but the fixture itself does not come into contact with water, such as an exterior building soffit. Wet location fixtures allow some contact of water with the exterior of the fixture. Vaportight fixtures allow the fixtures to operate in a very high humidity application like a shower stall.
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.
Decorative Bulbs
Light bulbs that come in many assorted and unusual shapes; and are different in appearance from the standard A-lamps. Most decorative bulbs have a screww-in base.
Die-Cast
A process that usually involves the high-pressure injection of zinc or aluminum into a hardened mold to produce a highly accurate part with high strength and detail.
Die-Formed
Die-forming to ensure highly accurate mass-produced parts at low cost. Die-forming uses large, high-tonnage presses with precision-formed and hard-stamping dies to pierce and bend the metal material. These large automated presses rapidly and economically produce complicated sheet metal parts with a high quality of fit.
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.
   E
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. See Luminous Efficacy
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).
Electromagnetic Spectrum
A continuum of electric and magnetic radiation that can be characterized by wavelength or frequency. Visible light encompasses a small part of the electromagnetic spectrum in the region from about 380 nanometers (violet) to 770 nanometers (red) by wavelength.
Electronic Ballast
A short name for a fluorescent high frequency electronic ballast. Electronic ballasts use solid state electronic components and typically operate fluorescent lamps at frequencies in the range of 25-35 kHz. The benefits are: increased lamp efficacy, reduced ballast losses and lighter, smaller ballasts compared to electromagnetic ballasts. Electronic ballasts may also be used with HID (high intensity discharge) lamps.
Electronic Dimming Ballast
A variable output electronic fluorescent ballast.
Elliptical Reflector (ER) Lamp
An incandescent lamp with a built-in elliptically-shaped reflecting surface. This shape produces a focal point directly in front of the lamp which reduces the light absorption in some types of luminaires. It is particularly effective at increasing the efficacy of baffled downlights.
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 Policy Act (EPACT)
Comprehensive energy legislation passed by the U. S. Congress in 1992. The lighting portion includes lamp labeling and minimum energy efficacy (lumens/watt) requirements for many commonly used incandescent and fluorescent lamp types. Federal Canadian legislation sets similar minimum energy efficacy requirements for incandescent reflector lamps and common linear fluorescent lamps.
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.
   F
F C
See Footcandle
Federal Ballast Energy Law
The Federal Ballast Energy Law (Public Law 100-357) was enacted in 1988 as part of the National Appliance Energy Conservation Amendments (NAECA '88). The law set minimum ballast efficacy standards for four major fluorescent lamp types. As of 1991, ballasts submitted for testing by the U.S. Department of Energy and complying with NAECA '88 provisions carry an E symbol on their labels. Ballasts exempt from NAECA included dimming ballasts and ballasts used in areas where ambient temperatures reached 0F or lower.
Federal Communications Commission (FCC)
The U. S. Federal agency that regulates emissions in the radio frequency portion of the electromagnetic spectrum. Part 18 of the FCC rules specifies electromagnetic interference (EMI) from lighting devices operating at frequencies greater than 9 kilohertz (kHz). Typical electronically-ballasted compact fluorescent lamps operate in the 24 - 100 kHz frequency range.
Field Angle
The angular dimension of the cone of light from reflectorized lamps (such as R and PAR types) encompassing the central part of the beam out to the angle where the intensity is 10% of maximum. See Beam Angle.
Filament
A wire coil made of tungsten that produces light when heated by an electric current. Lamp filaments are offered in a variety of designs optimized for specific applications.
Five-Stage Iron Phosphate Pretreatment
The standard process to best prepare sheet steel for painting. The steel is washed and rinsed with chemicals that clean and etch the metal and then force all moisture from the service to prevent it from combining with and threatening the integrity of the final paint service.
Flicker
Variation in light intensity due to 60 Hz operation. Can cause eye strain and fatigue due to stroboscopic effects.
Fluorescent Lamp
A high efficiency lamp utilizing an electric discharge through low pressure mercury vapor to produce ultra-violet (UV) energy. The UV excites phosphor materials applied as a thin layer on the inside of a glass tube which makes up the structure of the lamp. The phosphors transform the UV to visible light.
Footcandle (FC)
A unit of illuminance or light falling onto a surface. It stands for the light level on a surface one foot from a standard candle. One footcandle is equal to one lumen per square foot. See also Lux.
Footlambert
English unit of luminance. One footlambert is equal to 1/p candelas per square foot.
Full Spectrum Lighting
A marketing term, typically associated with light sources that are similar to some forms of natural daylight (5000K and above, 90+ CRI), but sometimes more broadly used for lamps that have a smooth and continuous color spectrum.
   G
G24q2
The designation for a socket base for a compact fluorescent lamp and LED or Induction Replacement Lamps. Since there are very many compact fluorescent lamp types and an equal number of socket types, a numbering system was developed to identify the different variations. "G" is for sockets that accept two or more lamp pins. "24" is the spacing in millimeters between the lamp pins in the base of the lamp. The "q" indicates that this socket accepts 4 (or quad) pins and the "2" indicates that this variation on this socket only accepts an 18W lamp to prevent users from mis-lamping the socket used in the fixture.
G-Lamp
Globular shaped light bulbs.
Glare
The effect of brightness or differences in brightness within the visual field sufficiently high to cause annoyance, discomfort or loss of visual performance.
GU-24 Bulbs/Sockets
The GU-24 socket and base system is designed to replace the Edison socket and base in energy efficient lighting fixtures. The GU-24 Light Bulb does not have the usual screw base, but instead has two bayonets protruding from the base (bi-pins). These insert into matching holes in the fixture's socket, and twist to lock into place. Twist and pull and the bulb come right out of the socket.
   H
Halogen Lamp
A halogen lamp is an incandescent lamp with a filament that is surrounded by halogen gases, such as iodine or bromine. Halogen gases allow the filaments to be operated at higher temperatures and higher efficacies. The halogen participates in a tungsten transport cycle, returning tungsten to the filament and prolonging lamp life.
Halogen-IR (HIR) Lamp
GE designation for high-efficiency tungsten halogen lamps. HIR lamps utilize shaped filament tubes coated with numerous layers of materials that transmit light but reflect the heat (infrared) back into the filament. This reduces the power needed to keep the filament hot.
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.
Hi-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-Intensity Discharge (HID) Lamp
A general term for mercury, metal halide and high-pressure sodium lamps. HID lamps contain compact arc tubes which enclose various gases and metal salts operating at relatively high pressures and temperatures.
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 (HPS) Lamp
HPS lamps are high intensity discharge light sources that product light by an electrical discharge though sodium vapor operating at relatively high pressures and temperatures.
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.
Hydro-Formed
This forming process allows the precision production of non-round asymmetric difficult-to-form reflector shapes. It allows designers to optimize reflector performance for non-centered lamps or fixtures that produce specific directional photometric properties.
   I
IBEW
Union Made International Brotherhood of Electrical Workers. This label represents that the fixture it is attached to is union-made. It is useful on larger construction jobs where the use of union-made products is encouraged. Job sites in certain larger cities strongly encourage the use of fixtures made by specific local unions.
IC Fixture
Insulated Ceiling Fixtures are allowed to be placed against and surrounded by building insulating material commonly found in areas such as residential attics.
IESNA
Abbreviation for Illuminating Engineering Society of North America.
Illuminance
The "density" of light (lumens/area) incident on a surface; i.e. the light level on a surface. Illuminance is measured in footcandles or lux.
Incandescent Lamp
A light source that generates light utilizing a thin filament wire (usually of tungsten) heated to white heat by an electric current passing through it.
Indirect Glare
Glare produced from a reflective surface.
Induction Lighting
Gases can be excited directly by radio-frequency or microwaves from a coil that creates induced electromagnetic fields. This is called induction lighting and it differs from a conventional discharge, which uses electrodes to carry current into the arc. Induction lamps have no electrodes inside the chamber and generally, therefore, have longer life than standard lamps.
Infrared Radiation
Electromagnetic energy radiated in the wavelength range of about 770 to 1,000,000 nanometers. Energy in this range cannot be seen by the human eye, but can be sensed as heat by the skin.
Instant Start
A type of ballast designed to start fluorescent lamps as soon as the power is applied. Most T8 fluorescent lamps are being operated on electronic instant-start ballasts. Slimline fluorescent lamps operate only on instant start circuits.
   K
Kelvin (K)
The Kelvin is a unit increment of temperature. The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero (0 K). The Kelvin scale and the kelvin are named after the Northern Irish physicist and engineer William Thomson, 1st Baron Kelvin (1824-1907), who wrote of the need for an “absolute thermometric scale”.
     The kelvin is often used in the measure of the color temperature of light sources. Color temperature is based upon the principle that a black body radiator emits light whose color depends on the temperature of the radiator. Black bodies with temperatures below about 4000 K appear reddish whereas those above about 7500 K appear bluish. Color temperature is important in the fields of image projection and photography where a color temperature of approximately 5500 K is required to match “daylight” film emulsions.
Kilowatt (kW)
The measure of electrical power equal to 1000 watts.
Kilowatt Hour (kWh)
The standard measure of electrical energy and the typical billing unit used by electrical utilities for electricity use. A 100-watt lamp operated for 10 hours consumes 1000 watt-hours (100 x 10) or one kilowatt-hour. If the utility charges $.10/kWh, then the electricity cost for the 10 hours of operation would be 10 cents (1 x $.10)
   L
Lamp
The term used to refer to the complete light source package, including the base, the inner parts, as well a the outer bulb or tube. "Lamp", of course, is also commonly used to refer to a type of small light fixture such as a table lamp.
Lamping
A technical term referring to the designer or manufacturer recommended wattage and lamp bulb type for a specific lamp or fixture or lighting application.
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 Depriciation 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.
LCL
(Light Center Length) The length, usually in inches, from a given point on the base of a lamp to its light center.
LED
Abbreviation for light emitting diode. An growing illumination technology originally used for miniature status lights and exit signs. Current technology is making LED light the new light source in commercial and residential applications for the 21st Century. Consumes low wattage and can have a rated life of greater than 80 years. Produces little heat, no UV rays, or noxious gasses.
Lens
Transparent or translucent medium that alters the directional characteristics of light passing through it. Usually made of glass or acrylic.
Life-Cycle Cost
The total costs associated with purchasing, operating, and maintaining a system over the life of that system.
Light
Radiant energy that can be sensed or seen by the human eye. Visible light is measured in lumens.
Light Center Length (L.C.L.)
The distance between the center of the filament, or arc tube, and a reference plane — usually the bottom of the lamp base.
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.
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 could operate at 12V and require 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 measure of the luminous flux or quantity of light emitted by a source. For example, a dinner candle provides about 12 lumens. A 60-watt Soft White incandescent lamp provides about 840 lumens.
Lumen Maintenance
A measure of how well a lamp maintains its light output over time. It may be expressed numerically or as a graph of light output vs. time.
Lumens Per Watt (lpW)
A ratio expressing the luminous efficacy of a light source.
Typical lamp efficacies:
• Incandescent lamps — 10-40
• Halogen incandescent lamps — 20-45
• Fluorescent lamps — 35-105
• Mercury lamps — 50-60
• Metal halide lamps — 60-120
• High-pressure sodium lamps — 60-140
Note: The values above for discharge lamps do not include the effect of the ballasts, which must be used with those lamps. Taking ballast losses into account reduces "system" or lamp-ballast efficacies typically by 10-20% depending upon the type of ballast used.
Luminaire
A complete lighting unit consisting of a lamp (or lamps), ballast (or ballasts) as required together with the parts designed to distribute the light, position and protect the lamps and connect them to the power supply. A luminaire is often referred to as a fixture.
Luminaire Efficiency
The ratio of total lumens emitted by a luminaire to those emitted by the lamp or lamps used in that luminaire.
Luminance
A photometric measure of "brightness" of a surface as seen by the observer, measured in candelas per square meter.
Luminous Efficacy
The light output (lumens) of a light source divided by the total power input (watts) to that source. It is expressed in lumens per watt.
Luminous Flux
The amount of light flowing over a given area in a period of time.
Lux (lx)
A unit of illuminance or light falling onto a surface. One lux is equal to one lumen per square meter. Ten lux approximately equals one footcandle.
   M
Magnetic Ballast
(Electromagnetic ballast) The most basic and oldest type of fluorescent ballasts. Consisting of a core of stacked steel plates wrapped with a coil of copper or aluminum wire (a basic electro-magnet), potted in an insulating material such as asphalt to conduct the heat of the ballast outward. The entire assembly is then put into a metal housing to prevent breakdown and shock hazard. Usually a separate starter is incorporated into this housing to provide the additional voltage needed when initially starting a fluorescent lamp. Some HID ballasts require an external ignitor.
Maintained Illuminance
Refers to light levels of a space at other than initial or rated conditions. This term considers light loss factors such as lamp lumen depreciation, luminaire dirt depreciation, and room surface dirt depreciation.
Maximum Overall Length (M.O.L.)
The end-to-end measurement of a lamp, expressed in inches or millimeters.
Mean Lumens
The average light output of a lamp over its rated life. Based on the shape of the lumen depreciation curve, for fluorescent and metal halide lamps, mean lumens are measured at 40% of rated lamp life. For mercury, high-pressure sodium and incandescent lamps, mean lumen ratings refer to lumens at 50% of rated lamp life. See Lumen Maintenance.
Mercury Lamp
A high-intensity discharge light source operating at a relatively high pressure (about 1 atmosphere) and temperature in which most of the light is produced by radiation from excited mercury vapor. Phosphor coatings on some lamp types add additional light and improve color rendering.
Metal Halide Lamp
A high-intensity discharge light source in which the light is produced by the radiation from mercury, plus halides of metals such as sodium, scandium, indium and dysprosium. Some lamp types may also utilize phosphor coatings.
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.
   N
Nadir
A reference direction directly below a luminaire, or “straight down” (0 degree angle).
Nanometer
A unit of wavelength equal to one billionth of a meter.
NEMA
Abbreviation for National Electrical Manufacturers Association.
NIST
Abbreviation for National Institute of Standards and Technology.
NOM
The Mexican standards testing agency.
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%).
   O
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.
   P
PAR Lamp
PAR is an acronym for parabolic aluminized reflector. A PAR lamp, which may utilize either an incandescent filament, a halogen filament tube or a HID arc tube, is a precision pressed-glass reflector lamp. PAR lamps rely on both the internal reflector and prisms in the lens for control of the light beam.
PAR 36
A PAR lamp that is 36 one-eighths of an inch in diameter, (4.5 inches), 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.
Phosphor
An inorganic chemical compound processed into a powder and deposited on the inner glass surface of fluorescent tubes and some mercury and metal-halide lamp bulbs. Phosphors are designed to absorb short wavelength ultraviolet radiation and to transform and emit it as visible light.
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.
Powder-Coated Finish
Used when a tougher, more durable paint coating is required with a final paint thickness up to 2.25 to 2.5 mm when dry. A special spray applicator applies an electro-statically charged dry resin powder that bonds to the charged metal surface being painted. Similar to baked enamel finished, it is used on parts that see more wear and tear or need better weather resistance.
Power Factor (PF)
A measure of the phase difference between voltage and current drawn by an electrical device, such as a ballast or motor. Power factors can range from 0 to 1.0, with 1.0 being ideal. Power factor is sometimes expressed as a percent. Incandescent lamps have power factors close to 1.0 because they are simple "resistive" loads. The power factor of a fluorescent and HID lamp system is determined by the ballast used. "High" power factor usually means a rating of 0.9 or greater. Power companies may penalize users for using low power factor devices.
Power Whips
Modular wiring whips are factory installed cabling systems that allows electricians to easily connect an entire series of lighting fixtures using a modular connector plug.
Preheat Circuit
A type of fluorescent lamp-ballast circuit used with the first commercial fluorescent lamp products. A push button or automatic switch is used to preheat the lamp cathodes to a glow state. Starting the lamp can then be accomplished using simple "choke" or reactor ballasts.
Protective Dust Guard
A plastic film placed on the decorative faces of reflectors and louvers (unfortunately, many end-users forget to take it off upon installation, impairing reflector performance).
   Q
Quad-Tube Lamp
A compact fluorescent lamp with a double twin tube configuration.
   R
R-Lamp
Reflector lamps are made of "soft" glass as oppose to the "hard" glass of a PAR lamp. This distinction concerns the glass structure and ability to deal with higher temperatures. They also differ in usually having their reflector source as an aluminum or silvery coating on the bulb itself.
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 Circuit
A fluorescent lamp-ballast circuit that utilizes continuous cathode heating, while the system is energized, to start and maintain lamp light output at efficient levels. Rapid start ballasts may be either electromagnetic, electronic or of hybrid designs. Full-range fluorescent lamp dimming is only possible with rapid start systems.
Rated Lamp Life
For most lamp types, rated lamp life is the length of time of a statistically large sample between first use and the point when 50% of the lamps have died. It is possible to define "useful life" of a lamp based on practical considerations involving lumen depreciation and color shift.
Reflectence
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.
Reflector Lamp (R)
A light source with a built-in reflecting surface. Sometimes, the term is used to refer specifically to blown bulbs like the R and ER lamps; at other times, it includes all reflectorized lamps like PAR and MR.
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 frame 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.
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.
   S
Scotopic/Photopic (S/P) Ratio
This measurement accounts for the fact that of the two light sensors in the retina, rods are more sensitive to blue light (pcotopic vision) and cones to yellow light (photopic vision). The pcotopic/photopic (S/P) ratio is an attempt to capture the relative strengths of these two responses. S/P is calculated as the ration of scotopic lumens to photopic lumens for the light source on an ANSI reference ballast. Cooler sources (higher color temperatures lamps) tend to have higher values of the S/P ratio compared to warm sources.
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.
Snap-Back
The potential or real situation where an energy-efficiency upgrade could be replaced with the original type of equipment. Installations that are subject to snap-back are not permanent.
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.
Specification Series (SP) Colors
Energy-efficient, all-purpose, tri-phosphor fluorescent lamp colors that provide good color rendering. The CRI for SP colors is 70 or above and varies by specific lamp type.
Specification Series Deluxe (SPX) Colors
Energy-efficient, all-purpose, tri-phosphor fluorescent lamp colors that provide better color rendering than Specification Series (SP) colors. The CRI for SPX colors is 80 or above and varies by specific lamp type. All GE CFL products use SPX phosphors.
Spectral Power Distribution (SPD)
A graph of the radiant power emitted by a light source as a function of wavelength. SPDs provide a visual profile or "finger print" of the color characteristics of the source throughout the visible part of the spectrum.
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.”
   T
T-Lamp
A lamp that is tubular in shape.
T8 Lamp
Industry standard for a fluorescent lamp that is 8 one-eighths (1 inch) in diameter.
T10 Lamp
Industry standard for a fluorescent lamp that is 10 one-eighths (1¼ inches) in diameter.
T12 Lamp
Industry standard for a fluorescent lamp that is 12 one-eighths (1½ inches) in diameter.
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.
Task Lighting
The lighting, or amount of light, used for a given task. Task lighting is localized to the visual task.
TCLP Test
The Toxicity Characteristic Leaching Procedure (TCLP) test, specified in the Resource Conservation and Recovery Act (RCRA) of 1990, is used to characterize fluorescent lamp waste as hazardous or nonhazardous waste. The TCLP test measures the ability of the mercury and/or lead in a lamp to leach from a landfill into groudwater.
THD Rating
Referring to Total Harmonic Distortion which is the distortion that sometimes occurs when the need for current is not in equilibrium with the supply of this current, for example, when turning on a ballast. THD can present a significant problem and if not pre-calculated and controlled can possibly overload the normal flow of current in the system. Low THD ballasts can be compared to surge protectors because they act to protect themselves and other electronic components by preventing power surges. The lower the THD rating of the ballast, therefore, the better (below 20 percent is preferred).
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.
Total Harmonic Distortion (THD)
A measure of the distortion of the input current on alternating current (AC) power systems caused by higher order harmonics of the fundamental frequency (60Hz in North America). THD is expressed in percent and may refer to individual electrical loads (such as ballast) or a total electrical circuit or system in a building. ANSI C82.77 recommends THD not exceed 32% for individual commercial electronic ballasts, although some electrical utilities may require lower THDs on some systems. Excessive THDs on electrical systems can cause efficiency losses as well as overheating and deterioration of system componenets.
Transformer
A device used in low voltage lamps to condition input voltage.
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)
Types of Bulbs
A letter or letters are used to designate the shape of bulbs. A number is used to indicate the bulb size. In the United States, light bulbs are measured in eighths of an inch around their maximum diameter.
   U
U-Lamp
A fluorescent lamp with two ends that is shaped like the letter "u".
Ultraviolet (UV) Radiation
Radiant energy in the range of about 100-380 nanometers (nm). For practical applications, the UV band is broken down further as follows:
• Ozone-producing — 180-220 nm
• Bactericidal (germicidal) — 220-300
• Erythemal (skin reddening) — 280-320
• "Black" light — 320-400
The International Commission on Illumination (CIE) defines the UV band as UV-A (315-400 nm); UV-B (280-315 nm) and UV-C (100-280 mm).
Underwriters Laboratories (UL)
A private organization which tests and lists electrical (and other) equipment for electrical and fire safety according to recognized UL and other standards. A UL listing is not an indication of overall performance. Lamps are not UL listed except for compact fluorescent lamp assemblies - those with screw bases and built-in ballasts.
UL 1570
Underwriters Laboratories Inc. requirements for fluorescent fixtures.
UL 935
Underwriters Laboratories Inc. requirements for fluorescent ballasts.
   V
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 (typically 800 mA) or standard output lamp (typically 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. A measurement of the electromotive force in an electrical circuit or device expressed in volts. Voltage can be thought of as being analogous to the pressure in a waterline.
   W
Wallwasher
Describes luminaires that illuminate vertical surfaces.
Watt
A unit of electrical power. Lamps are rated in watts to indicate the rate at which they consume energy. See Kilowatt Hour.
Wireway Cover
A cover of a fluorescent fixture that encloses access to the splice compartment and the ballast location.
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).
   Z
Zenith
The direction directly above the luminaire (180° angle).

 

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