Terminology

American National Standards Institute (ANSI)

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.

Amperes ("Amps")

("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)

Group that generates product performance standards for many U.S. industries.

ANSI Watts

Measurement of electrical power used by the ballast and lamps when tested per ANSI standards.

Anti-Arc Circuit

Circuitry used to restart the lamps without resetting the power to the ballast.

Anti-Striation Circuit

Circuitry used to prevent striations or spiraling in energy saving lamps due to low temperature or low current operation.

Arc (Lamp)

Intense luminous discharge formed by the passage of electric current across a space between electrodes.

Arcing of output leads

Generation of an electrical arc between output leads of a ballast or output leads to ground.

Auto-Restrike

Circuitry used to restart the lamps without resetting the power to the ballast.

Autotransformer

A tapped winding transformer that changes the voltage available locally to the voltage required by a particular load.

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 Efficacy Factor (BEF)

Measure used to compare various lighting systems based upon light output and power input. Higher BEF is favorable. BEF = Ballast Factor x 100 / Input Watts

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.

Ballast Losses

Power that is supplied to the ballast but is not converted into light energy.

Ballast Noise "Hum"

Sound made by operating Core & Coil assemblies in both electromagnetic and electronic ballasts, generated by the vibration of laminations in the electromagnetic field that transforms the voltage and current used by discharge lamps. The sound made by high frequency electronic ballasts is lower and any noise made by models with electronic power factor correction circuits is inaudible.

Ballast Regulation

The ability of a ballast to control lamp wattage (and therefore light output) when subject to changes in line voltage.

Bayonet

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.

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. See also Field Angle.

Beam Spread

(in any plane) the angle between the two directions in the plane in which the candlepower is equal to a stated percent (usually ten percent) of the maximum candlepower in the beam.

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.

Bin

In LED's, the systematic dividing of distribution of performance parameters (Flux, Color or CCT, and Vf) in to smaller groups that meet aesthetic requirements of the assembly.

Binning

In LED's, the subdivision of the manufactured "distribution" into bins common operating parts (color, flux, forward voltage).

Bottom Exit

A configuration with leads or a wire-trap on the bottom or base of the ballast. This type of Configuration is usually used when the ballast is mounted on to a junction box plate.

Brightness

See Luminance

Burn-in test

Test performed on electronic product that simulates conditions encountered in actual operation to weed out initial failures.

Canadian Standards Association (CSA)

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.

Candlepower

An obsolete term for luminous intensity; current practice is to refer to this simply as candelas.

Capacitor

Device in ballast that stores electrical energy.

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.

Centigrade (C)

Celsius temperature scale where 0°C = 32°F and 100°C = 212°F.

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.

Chromaticity

the aspect of color that includes consideration of its dominant wavelength and purity.

Coefficient of Utilization (CU)

In general lighting calculations, the ratio of the luminous flux (lumens) from a luminaire received on the work-plane to the lumens emitted by the luminaire's lamps alone.

Coil

Windings of copper or aluminum wire around the core in electromagnetic ballast that transforms the voltage from input to output.

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 Kelvin (K), 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.

Core

Component of electromagnetic ballast that is surrounded by the coil and comprised of steel laminations or solid ferrite material.

Core & Coil Ballast

Another term for electromagnetic ballast.

Crest factor

Ratio of peak lamp current to RMS (average) lamp current.

CSA-E

Marking on ballast that shows compliance with Canadian Ballast Energy Law.

Current

A measure of the flow of electricity, measured in amperes (A)

Cut-off Angle

(of a luminaire) the angle from the vertical at which a reflector, louver or other shielding device cuts off direct visibility of a light source. It is the complementary angle of the shielding angle.

Cycling

See 'Ballast Cycling'.

DALI (Digitally Addressable Lighting Interface)

An industry standard system protocol that allows components from different manufacturers (ballasts, controls systems, sensors, controllers, switches, etc) to be mixed together seamlessly into complete systems.

DC forward current

Continuous direct current applied which is constant over time.

Design Lumens

The amount of light that the lamp produces after it has operated for approximately 40 percent of its rated life.

Die

Chip: heart of the LED.

Diffuser

A device to redirect of scatter the light from a source by the process of diffuse transmission.

Diode

A two-electrode device with an anode and a cathode that passes current in only one direction. It may be designed as an electron tube or as a semiconductor device.

Direct Current (DC)

An electrical current flowing steadily in one direction only.

Direct Glare

Glare resulting from high luminance or insufficiently shielded light sources in the field of view, or from reflecting areas of high luminance. It is usually associated with bright areas such as luminaires, ceilings and windows that are outside the visual task or region being viewed.

Direct Lighting

Lighting by luminaires distributing 90 to 100 percent of the emitted light in the general direction of the surface to be illuminated. The term usually refers to light emitted in a downward direction. (See accent lighting.)

Directional Lighting

Illumination on the work-plane or on an object predominantly from a single direction.

Discharge Lamp

A light producing device that depends on an electric arc, rather than a filament, to create illumination.

Driver

Electronics used to power illumination sources. Ballast.

Efficacy

efficiency of a light source expressed in lumens per watt (LPW or lm/W). Also see Luminous Efficacy

Electrical Testing Laboratory (ETL)

Independent electrical testing laboratory, which performs ballast testing.

Electromagnetic Ballast

A ballast that, with the aid of electronic components converts 60 Hz. input voltage and current to high frequency (20 kHz to 60 kHz.) to operate fluorescent and high intensity discharge (HID) lamps.

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.

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.

Emitter

The electrode in a transistor where electrons originate

Energy

A measure of work done by an electrical system over a given period of time, often expressed in kilowatt-hours (kWh).

Energy Policy Act (EPAct)

Comprehensive energy legislation passed by the U. S. Congress in 1992 and significantly overhauled in 2005. Covers energy generation, transmission, distribution and energy efficiency. Three major systems include: Interior Lighting, HVAC/Hot Water and Building Envelope. Rewards improvements over ASHRAE 90.1-2001 standard by offering one-time tax deductions on capital investment for energy efficient systems put in service January 1, 2006 - December 31, 2007.

ESCO

Energy Saving Service Company

Feedback Signal

A feedback signal, or control signal, regulates power through the LED driver to produce various effects in LEDs.

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

Coated coil of special wire that emits electrons or light when heated.

Filament Voltage

Voltage applied to heat the lamp filament coil. Also called electrode or filament heating.

Filter

Functional grouping that limits interference feedback into the power source and protests internal ballast components.

Fluorescence

Emission of visible light by the absorption of energy from another source.

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.

Footcandles (fc)

Measure of light level on a surface that is being illuminated. One footcandle is equal to one lumen per square foot. See also Lux.

Frequency

Rate of alteration in an AC current. Expressed in cycles per second or Hertz (Hz).

General Lighting

Lighting designed to provide a substantially uniform illuminance throughout an area, exclusive of any provision for special local requirements.

Glare

Excessive brightness that may be caused by either direct or indirect viewing of a light source; any brightness or brightness relationship that annoys, distracts or reduces visibility.

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.

Harmonic Distortion

A measurement of the magnitude of voltage and current harmonics as compared with the amplitude of the fundamental frequency. Harmonic distortion can be generated by a load and fed back into the AC mains, causing distortion of the sinusoidal waveform.

Harmonics

 Refers to components of the overall frequency, an integral multiple of the fundamental sinewave frequency.

Hertz (Hz)

 Unit used to measure frequency (cycles per second) of alternating current or voltage.

High Flux

 LEDs that are approximately 1.0 watts or more and provide a significantly high light intensity. Operate at 350mA.

High Frequency Electronic Ballast

In this book, refers to the operation of electronic ballasts as frequencies > 20,000 Hertz (20 kHz). 

High Light Output

 Ballast with a nominal ballast factor of 1.18.

High Power Factor Ballast (HPF)

 A ballast in which the power factor is greater than 0.9 (90%). These ballasts require less line current than normal power factor ballast.

High Reactance AutoTransformer Ballast (HX)

 HID ballast used when the input voltage does not meet the starting voltage requirement for a lamp. The ballast will transform the input voltage to the required level.

High-Intensity Discharge (HID) Lamp

 A general term for mercury, metal halide and high-pressure sodium. HID lamps contain compact arc tubes which enclose various gases and metal salts operating at relatively high pressures and temperatures to produce light.

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 Time

The time it takes a HID lamp to restart and reach 90% of its light output after going from on to off to on. Typical restart times are 1 to 2 minutes for HPS and 5 to 20 minutes for Metal Halide. 

IES (Illuminating Engineering Society)

 Recognized technical authority on the advancement of the art and science of illumination and its dissemination.

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.

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.

Initial Lumens

 The measure of the amount of light a lamp produces after it has been operating 100 hours.

Input Voltage

 Voltage, provided by a power line or power supply, to the ballast or driver.

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.

Kilohertz (KHz)

 One thousand Hertz (cycles per second).

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)

Lamp

 The term used to refer to the complete light source package, including 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.

Life

 See Rated Lamp Life.

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. Refer to the following chart for reference plane locations.

Light Emitting Diodes (LED)

 A solid-state semiconductor device that converts electrical energy directly into light. On its most basic level, the semiconductor is comprised of two regions. The p-region contains positive electrical charges while the n-region contains negative electrical charges. When voltage is applied and current begins to flow, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths.

Louver

 A series of baffles used to shield a source from view at certain angles or to absorb unwanted light. The baffles are usually arranged in a geometric pattern.

Low Flux

 LEDs that are typically .1 to .4 watts each, and are arranged in clusters or arrays to create a collective light source. These systems operate a 12vdc or 24 vdc.

Low Power Factor Ballast (LPF)

 Ballast with a power factor of 0.79 or less - also called normal power factor (NPF) ballast. LPF ballast requires about twice the line current of HPF ballast so fewer LPF ballasts can be installed on a circuit, which increases installation cost.

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 Depreciation

 The decrease in lumen output of a light source over time. Also see Lumen Maintenance.

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.

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.

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.

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.

Nanometer

 A unit of wavelength equal to one billionth of a meter.

National Electric Code (NEC)

 A nationally accepted electrical installation code developed by the National Fire Protection Association to reduce the risk of fire.

National Electrical Manufacturers Association (NEMA)

 U.S. based association that sets many common standards used in electrical products

National Energy Standards for Fluorescent Ballasts

 A federal law enacted in 1988 that sets energy standards for ballasts consistent throughout the United States.

Non-PCB Capacitor

 Capacitor used in ballasts to help provide power factor correction.

Normal Light Output

 Ballast with a nominal ballast factor of 0.88 for most T8 ballasts, and 1.00 for most T5 and dimming ballasts.

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.

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.

Powder coating

Powder coating is the process of coating a surface in which a powder material is applied using an electrostatic or compressed air method. The applied powder is then heated (cured) to its melting point, after which it flows to form a smooth film which dries to a firm, durable finish very resistent to scratches, cracking, peeling, UV rays and rust.

Power

 The amount of energy consumed or needed by a device (ballast, lamp, or ballast plus lamp) to perform its function. Power is measured in watts.

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.

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.

Probe Start

 Method of starting mercury vapor and specific metal halide lamps in which an additional electrode at one end of the arc tube assists in lamp starting.

Pulse Start

 Method of starting high pressure sodium and specific metal halide lamps in which a high voltage starting pulse starts the lamps.

Quality of Light

 Pertains to the distribution of luminance in a visual environment. The term is used in a positive sense and implies that all luminances contribute favorably to visual performance, visual comfort, ease of seeing, safety and esthetics for the specific visual tasks involved.

Quantity of Light

 The product of the luminous flux by the time it is maintained. It is the time integral of luminous flux.

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.

Rapid Start Lamp

 Fluorescent lamp that requires filament heating before igniting and producing light.

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.

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.

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.

Shielding

A general term to include all devices used to block, diffuse or redirect light rays, including baffles, louvers, shades, diffusers and lenses. 

Shielding Angle

 The complementary angle of the cut-off angle of a luminaire.

Slimline Lamp

 Fluorescent lamp, which has single pin contacts, that requires no filament heating to ignite.

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.

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.

Starting Temperature

 The minimum ambient temperature at which the lamp will start. Light output may be affected due to lamp characteristics.

System efficacy

 Overall efficiency of the lamp/ballast system. System efficacy = total lamp lumens / system wattage.

T12, T10, T8, T5

 Industry standard naming for a fluorescent lamp. (T= Tubular and the numbers that follow represent the diameter in 1/8 inch increments.)

TCLP Test

 Toxicity Characteristic Leaching Procedure - EPA test used to identify hazardous waste.

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 components.

Typical lamp efficacies:

• Thomas Edison's first lamp 1.4 lpW

• 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.

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. End use products such as lighting fixtures, fully encased ballasts, and home appliances are examples of UL Listed products and bear the UL logo. Components such as HID open core & coil ballasts, electrical insulating materials are UL Component Recognized products and bear the UL Component Recognition logo. Lamps are not UL listed except for compact fluorescent lamp assemblies - those with screw bases and built-in ballasts.

Voltage

 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.

Watt

 A unit of electrical power. Lamps are rated in watts to indicate the rate at which they consume energy. See Kilowatt Hour.

Work Plane

 The plane at which work usually is done, and on which the illuminance is specified and measured. Unless otherwise indicated, this is assumed to be a horizontal plane 0.76 meters (30 inches) above the floor