General Lighting Glossary

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• Accent Lighting
  Directional lighting to emphasize a particular object or draw attention to a display item.
  
  
• Ambient Lighting
  The general lighting present in an area --excluding task lighting and accent lighting but including general lighting and daylight streaming in.
  
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• Base or 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 bipin bases are common for linear fluorescent lamps.
  
  
• 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. The beam angle sometimes called "beam spread" is often part of the ordering code for the reflectorized lamps.
  
  
• Beam Lumens
  The total lumens present within the portion of the beam contained in the beam angle.
  
  
• Beam Spread (Approximate)
  The total angle of the directed beam (in degrees horizontal or vertical) to where the intensity of the beam falls to 50% or 10% of the maximum candlepower value as indicated.
  
  
• Bi-Pin
  Any base with two metal pins for electrical contact. 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.
  
  
• Bollard
  A short, thick post with a light at its top, used for grounds and outdoor walkway lighting.
  
  
• Bulb
  A loose way of referring to a lamp. "Bulb" refers to the outer glass bulb containing the light source.
  
  
• Brightness
  Brightness can refer to any of several technical terms used in lighting and is, therefore, ambiguous.
  
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• 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.
  
  
• Candlepower (Mean Spherical)
  Initial mean spherical candlepower at the design voltage. Mean spherical candlepower is the generally accepted method of rating the total light output of miniature lamps. To convert this rating to lumens, multiply it by 12.57 (4 pi).
  
  
• Candlepower Distribution Curve
  A graphical presentation of the distribution of light intensity of a light source, usually a reflector lamp or luminaire.
  
  
• Chromaticity
  Measure to identify the color of a light source, typically expressed as (x,y) coordinates on a chromaticity chart (See COLOR TEMPERATURE).
  
  
• Chromaticity Coordinates
  A system for measuring the color of the light emitted from a light source--either a primary source like a lamp or a secondary source like an illuminated object. Usually two numbers, x and y coordinates ranging from 0 to 1 specify the chromaticity.
  
  
• 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 (See CHROMATICITY).
  
  
• Cost of Light
  Usually refers to the cost of operating and maintaining a lighting system on an ongoing basis. The 88-8-4 rule states that (typically) 88% is the cost of electricity, 8% is labor and only 4% is the cost of lamps. (ACCORDING TO GE)
  
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• Dimmable
  Whether or not the lamp lumens can be varied while maintaining reliability.
  
  
• Dimmer, Dimming Control
  A device used to lower the light output of a source, usually by reducing the wattage it is being operated at. Dimming controls are increasing in popularity as energy conserving devices.
  
  
• Department of Transportation (DOT)
  The US Department of Transportation. www.usdot.gov
  
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• Efficacy
  A measurement of how effective the light source is in converting electrical energy to LUMENS of visible light. Expressed in LUMENS-PER-WATT (LPW) this measure gives more weight to the yellow region of the spectrum and less weight to the blue and red region where the eye is not as sensitive.
  
  
• Efficiency
  The efficiency of a light source is simply the fraction of electrical energy converted to light, i.e. watts of visible light produced for each watt of electrical power with no concern about the wavelength where the energy is being radiated. For example, a 100 watt incandescent lamp converts 7% of the electrical energy into light; discharge lamps convert 25% to 40% into light. The efficiency of a luminaire or fixture is the percentage of the lamp lumens that actually comes out of the fixture (See LUMINOUS EFFICACY).
  
  
• Electromagnetic Inference (EMI)
  High frequency electronic ballasts and other electronic devices can produce a small amount of radio waves which can interfere with radio and TV. Federal mandated requirements must be met for EMI levels before an electronic device is considered FCC compliant. (FCC is the Federal Communications Commission.)
  
  
• 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 (See ELECTROMAGNETIC BALLAST).
  
  
• 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 Policy Act (EPACT) Indicator
  Means this lamp is Federally regulated for Energy Efficiency (See ENERGY POLICY ACT).
  
  
• Eye Sensitivity
  A curve depicting the sensitivity of the human eye as a function of wavelength (or color). The peak of human eye sensitivity is in the yellow-green region of the spectrum. The normal curve refers to photopic vision or the response of the cones.
  
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• 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).
  
  
• Flicker
  The periodic variation in light level caused by AC operation that can lead to strobe effects.
  
  
• Flood
  Used to refer to the beam pattern of a reflector lamp, which disperses the light over a wide beam angle, typically 20 degrees or more. ("Flood" as opposed to "spot")
  
  
• Floodlight
  A luminaire used to light a scene or object to a level much brighter than its surroundings. Usually floodlights can be aimed at the object or area of interest.
  
  
• Fluorescence
  A physical phenomenon whereby an atom of a material absorbs a photon of light an immediately emits a photon of longer wavelength. If there is a significant delay the phenomenon is called phosphorescence rather than fluorescence. It is interesting that "phosphors" used in lamps exhibit "fluorescence," not "phosphorescence." (See PHOSPHOR)
  
  
• 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.
  
  
• Frequency (Nominal Operations)
  The stated operating frequency in Hz of a discharge lamp.
  
  
• 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. Most rescently used to describe LED lighting that incorporates Red, Green and Blue LEDs to create polychromatic light.
  
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• General Lighting
  (See AMBIENT LIGHTING)
  
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• 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.
  
  
• High-Bay Lighting
  Lighting designed for (typically) industrial locations with a ceiling height of 25 feet and above.
  
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• Ignitor
  An electronic device providing a high voltage pulse to initiate an electrical discharge. Typically, the ignitor is paired with or is a part of the ballast (See STARTER).
  
  
• 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. Illuminance Meter A device that measures the illuminance at a location calibrated either in footcandles or in 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 Lighting
  The method of lighting a space by directing the light from luminaires upwards towards the ceiling. The light scattered off the ceiling produces a soft, diffuse illumination for the entire area.
  
  
• 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.
  
  
• Inverse Square Law
  Formula stating that if you double the distance from the light source, the light level goes down by a factor of 4, if you triple the distance, it goes down by a factor of 9, and so on.
  
  
• Isocandela Plot
  A plot with lines connecting points of equal luminous intensity around a source.
  
  
• Isolux Plot (or Isofootcandle Plot)
  A line plotted to show points of equal illuminance (lux or footcandles) on a surface illuminated by a source or sources.
  
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• Kelvin
  A unit of temperature starting from absolute zero, parallel to the Celsius (or Centigrade) scale. 0C is 273K.
  
  
• 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)
  
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• 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
  
  
• Lens
  A transparent or semi-transparent element which controls the distribution of light by redirecting individual rays. Luminaires often have lenses in addition to reflectors.
  
  
• 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 Emitting Diode (LED)
  A solid that directly converts electrical impulses into light. Some LED's today incorporate fluorescent materials to change the color characteristics of the emitted light.
  
  
• Lighting Industry Federation (LIF)
  Code For Stage & Studio lamps, these are assigned by the Lighting Federation of London U.K. They ensure electrical and mechanical interchangeability of similarly coded lamps. LIF codes are divided into groups according to the primary application of the lamps.
  
  
• Light Loss Factor
  The product of all factors that contribute to lowering the illumination level including reflector degradation, dirt, lamp depreciation over time, voltage fluctuations, etc.
  
  
• Light Meter
  (See ILLUMINANCE METER)
  
  
• Light Pollution
  Light that is directed to areas where it is not needed, and thereby interferes with some visual act. Light pollution directed or reflected into the sky creates a "dome" of wasted light and makes it difficult to see stars above cities.
  
  
• Light Trespass (Spill Light)
  Light that is not aimed properly or shielded effectively can spill out at into areas that don't want it: it can be directed towards drivers, pedestrians or neighbors. It is distracting and annoying and can sometimes be disabling.
  
  
• Lumens
  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.
  
  
• Luminaire Efficiency
  The ratio of total lumens emitted by a luminaire to those emitted by the lamp or lamps used in that luminaire.
  
  
• Luminous Efficacy
  (See EFFICACY)
  
  
• 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.
  
  
• Luminance
  A measure of "surface brightness" when an observer is looking in the direction of the surface. It is measured in candelas per square meter (or per square foot) and was formerly referred to as "photometric brightness."
  
  
• 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. (See FOOTCANDLE)
  
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• 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).
  
  
• Medium Base
  Usually refers to the screw base typically used in household incandescent lamps. There is also the medium bipin base commonly used in T12 and T8 fluorescent lamps.
  
  
• Mogul Base
  A screw base used on larger lamps, e.g. many HID lamps.
  
  
• Monochromatic Light
  Light with only one wavelength (i.e. color) present.
  
  
• MR-16 and MR-11
  A line of low voltage compact reflector lamps used for accent and spot lighting. The 16 and 11 refer to 16 eighths of an inch diameter and 11 eighths.
  
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• Nanometer
  A unit of wavelength equal to one billionth of a meter.
  
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• Operating Voltage
  The required voltage or voltage supply to opperate a lamp.
  
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• PAR Lamp
  PAR is an acronym for parabolic aluminized reflector. A PAR lamp, which may utilize either an incandescent filament, a halogen filament tube, a HID arc tube or an LED Light Engine, 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 (See FLOURESCENCE).
  
  
• Photometry
  The measurement of light and related quantities.
  
  
• 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.
  
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• Radiation
  A general term for the release of energy in a "wave" or "ray" form. All light is radiant energy or radiation, as is heat, UV, microwaves, radio waves, etc.
  
  
• 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 (See LIFE).
  
  
• Reflectance
  The ratio of light reflected from a surface to that incident upon it. 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.
  
  
• Room Cavity Ratio (RCR)
  A shape factor (for a room, etc.) used in lighting calculations. RCR = 5H (L+W) / L x W, or, alternately, RCR = (2.5) Total Wall Area / Floor Area. Where H = height, L = length and W = width of the room. A cubical room will have an RCR of 10; the flatter the room the lower the RCR.
  
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• 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.
  
  
• Spectrum
  The distribution of a characteristic of a physical system or phenomenon, especially: The distribution of energy emitted by a radiant source, as by an incandescent body, arranged in order of wavelengths. The distribution of atomic or subatomic particles in a system, as in a magnetically resolved molecular beam, arranged in order of masses. See also SPECTRAL POWER DISTRIBUTION (SPD).
  
  
• Specular Reflection
  Reflection from a smooth, shiny surface, as opposed to diffuse reflection.
  
  
• Spot
  A colloquial term referring to a reflector lamp with a tight beam of light, typically around 10 degrees or less. It comes from the fact that such a lamp produces a narrow spot of light as opposed to a wide flood of light.
  
  
• System
  A term referring to the lamp/light engine and ballast/transformer combination, and sometimes to the entire lighting delivery system including the fixture, the optics, the particular layout and the lighting controls.
  
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• Task Lighting
  Supplemental lighting provided to assist in performing a localized task, e.g. a table lamp for reading or inspection.
  
  
• Total Harmonic Distortion (THD)
  A measure of the distortion caused by ballasts and other inductive loads 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.
  
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• 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.
  
  
• 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).
  
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• Valance Lighting
  Lighting from light sources on a wall typically above eye level, shielded by horizontal panels. The light may be upward or downward directed.
  
  
• Veiling Reflection
  Effective reduction in contrast between task and its background caused by the reflection of light rays; sometimes called "reflected glare." You might have dealt with veiling reflections when you have to tilt a shiny magazine to avoid glare so as to read it, or struggled with reading a computer monitor because of the reflection of a window or a light fixture (See GLARE).
  
  
• Visual Comfort Probability (VCP)
  For a given lighting scheme, VCP is a ratio expressed as a percent of people who, when viewing from a specific location and in a specified direction, find the system acceptable in terms of glare (See GLARE).
  
  
• Visual Task
  The task associated with seeing; objects and details that must be seen to perform an activity.
  
  
• Volt
  A measure of "electrical pressure" between two points. The higher the voltage, the more current will be pushed through a resistor connected across the points. The volt specification of an incandescent lamp is the electrical "pressure" required to drive it at its designed point. The "voltage" of a ballast (e.g. 277 V) refers to the line voltage it must be connected to.
  
  
• 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.
  
  
• Voltage (Design)
  For Automotive lamps, voltage at which the lamp is designed to provide the amperes, candlepower, and laboratory life characteristics. For Projection lamps, the voltage shown is the design voltage of the lamp, on which the life and wattage ratings are based. Lamps for which 115-120 is shown in the Volts column are designed at 118 volts. Lamps are available only in the design voltage(s) shown. When ordering lamps listed for more than one voltage, be sure to specify the voltage required. (Supply voltage variation can significantly affect lamp life.)
  
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• Warm White
  Refers to a color temperature around 3000K, providing a yellowish-white light.
  
  
• Watt
  A unit of electrical power. Lamps are rated in watts to indicate the rate at which they consume energy (See KILOWATT HOUR).
  
  
• Wavelength
  The distance between two neighboring crests of a traveling wave. The wavelength of light is between 400 and 700 nanometers.
  
  
• Work Plane
  Plane at which work is done and at which illumination is specified and measured; unless otherwise indicated, it is assumed to be a horizontal plane 30 inches above the floor (table-top height) having the same area as the floor.
  
  
• Working Distance (Typical)
  Working Distance shown is the distance from the front surface of the reflector rim to the work plane, in the optical system for which the lamp was first designed. In most cases, it provides a uniform plane of light for the intended aperture.
  
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Most deffinitions are taken from GE Lighting bulletins and handouts and/or dictionary.com