Glossary of Lighting Terms

-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 -

-A-
Accent Lighting
 Directional lighting to emphasize a particular object or draw attention to an item.
back to top

Adaptation
 The process by which the retina of the eye becomes accustomed to more or less light than it was exposed to during an immediately preceding period. It results in a change in the sensitivity of the eye to light.
back to top

Ambient Lighting
The general lighting present in an area --excluding task lighting and accent lighting but including general lighting and daylight streaming in.
back to top

Amperes
("Amps.") A measure of electrical current. In incandescent lamps, the current is related to voltage and power as follows: Watts (power) = Volts x Amps (current).
back to top

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.
back to top

ANSI Ballast Type
Ballast type used to operate lamp in accordance with ASNI standard.
back to top

ANSI Codes
These are 3-letter codes assigned by the American National Standards Institute. They provide a system of assuring mechanical and electrical interchangeability among similarly coded lamps from various manufacturers.
back to top

Application
Also called "lighting application," it refers to the particular use the lamp is being put to. (e.g. high-bay industrial application or retail lighting application.) The term can also refer in a general way to "application engineering" which deals with specific paramters and usage of light sources. (e.g. how to do a lighting layout, where to place fixtures and so on.)
back to top

Arc
A general term for a high intensity electrical discharge occurring between two electrodes in a gaseous medium, usually accompanied by the generation of heat and the emission of light
back to top

Arc Lamp
A light source containing an arc (see above). Also called a discharge lamp, or an arc discharge lamp.
back to top

Arc Length
In High Intensity Discharge lamps this is the distance between the electrode tips, which represents the physical length of the electrical discharge.
back to top

Atmosphere
This field designates the type of gas or vacuum filling a volume or chamber of the lamp. This chamber might contain a filament or it might refer to the bulb which contains the arc tube.
back to top

-B-

 Ballast
 A device used with an electric-discharge lamp to obtain the necessary circuit conditions for starting and operating such lamps as fluorescent and high intensity discharge (HID).
back to top

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.
back to top

Base
The part of a light bulb that fits into the socket. Base type diagram.
back to top

Base Temperature (Maximum)
The maximum operating temperature permitted for the base in Celsius. Fixture manufacturers need to ensure that these conditions are satisfied in their fixture.
back to top

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.
back to top

Beam Angle
The angle between the two directions for which the intensity is 50% of the maximum intensity.
back to top

Beam Spread
The total angle of the directed beam to where the intensity of the beam falls to 50% or 10% of the maximum candlepower value as indicated.
back to top

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.
back to top

Blackbody
A hot body with an incandescent black surface at a certain temperature used as a standard for comparison. Note that a black surface is the best radiator possible. A tungsten filament will emit slightly less radiation than a blackbody at the same temperature.
back to top

Black Light
A popular term referring to a light source emitting mostly near UV (320 to 400 nm) and very little visible light.
back to top

Blacktop
Whether or not the top of the miniature lamp has a blacktop coating. The coating is used to control unwanted brightness or glare.

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.
back to top

Bulb Material or Coating
The type of glass (or quartz) used in the glass envelope surrounding the light source. The material can also have coatings applied to achieve particular performances.
back to top

Brightness
Brightness can refer to any of several technical terms used in lighting and is, therefore, ambiguous
back to top

-C-

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.
back to top

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.
back to top

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

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).
back to top

Candlepower Distribution Curve
A graphical presentation of the distribution of light intensity of a light source, usually a reflector lamp or luminaire.
back to top

Cathode Resistance
Resistance of the cathode in a Fluorescent lamp. It is measured "cold" before the lamp is turned on (Rc) or "hot" after the lamp is turned on (Rh). The ratio of the hot resistance to the cold resistance is also measured (Rh/Rc).
back to top

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.
back to top

Chromaticity
Measure to identify the color of a light source, typically expressed as (x,y) coordinates on a chromaticity chart.
back to top

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.
back to top

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.
back to top

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.
back to top

Color Temperature
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.
back to top

Compact Fluorescent Lamp
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.
back to top

Cool White
A term loosely used to denote a color temperature of around 4100 K. The Cool White (CW) designation is used specifically for T12 and other fluorescent lamps using halophosphors and having a CRI of 62.
back to top

Cosine-Corrected
An illuminance meter that measures the light level correctly irrespective of the angle the light is coming from.
back to top

Crest Factor (Max Current)
The ratio of the peak lamp current to average lamp operating current (RMS). The lower the current crest factor is, the gentler the ballast is on the lamp.
back to top

Current Type
Whether the operational voltage is based on Alternating Current (AC) or Direct Current (DC).
back to top

-D-

Daylight Harvesting
Lighting design for building interiors that makes of daylight as a way of reducing energy consumption.
back to top

Daylight Lamp
A lamp resembling the color of daylight, typically with a color temperature of 5500 K to 6500K
back to top

Dimmable
Whether or not the lamp lumens can be varied while maintaining reliability.
back to top

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.
back to top

Distance Between Legs
For U-shaped Fluorescent lamps, this measurement is the average distance between the inner walls of the legs.
back to top

Distance Between Leg Centers
For U-shaped Fluorescent lamps, this measurement is the average distance between the centers of each leg.
back to top

Distance Outside Legs
For U-shaped Fluorescent lamps, this measurement is the average distance to the outside of each leg.
back to top

Department of Transportation (DOT) Type
The US Department of Transportation lamp number stamped in the glass lens or on the base of headlamps.
back to top

-E-

Eccentricity (Maximum)
In High Intensity Discharge lamps the Bulb to Arc Angle is the angle off of center between electrodes and bulb. The Bulb to Base Angle is the angle off of center that the bulb is from the base.
back to top

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.
back to top

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.
back to top

Electrical Discharge
A condition under which a gas becomes electrically conducting and becomes capable of transmitting current, usually accompanied by the emission of visible and other radiation. An electric spark in air is an example of an electrical discharge, as is a welder's arc and a lightning bolt.
back to top

Electrodeless Lamps
Light sources where the discharge occurs in a chamber with no electrodes (no metal.) The energy for the discharge is supplied by radio frequency excitation, e.g. microwaves.
back to top

Electromagnetic Ballast
A ballast used with discharge lamps that consists primarily of transformer-like copper windings on a steel or iron core.
back to top

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.
back to top

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.
back to top

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 high intensity discharge (HID) lamps.
back to top

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.
back to top

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.
back to top

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.
back to top

-F-

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.
back to top

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.
back to top

Filament Design
Filaments are designated by a letter combination in which C is a coiled wire filament, CC is a coiled wire that is itself wound into a larger coil, and SR is a straight ribbon filament. Numbers represent the type of filament-support arrangement.
back to top

Flicker
The periodic variation in light level caused by AC operation that can lead to strobe effects.
back to top

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")
back to top

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.
back to top

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”.
back to top

Fluorescent Lamp
A high efficiency lamp utilizing an electric discharge through low pressure mercury vapor to produce ultraviolet (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.
back to top

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.
back to top

Footlambert
An obsolete term referring to a luminance of 1/? candelas per square foot.
back to top

Frequency (Nominal Operations)
The stated operating frequency in Hz of a discharge lamp.
back to top

Fovea, Foveal Vision
A small region of the retina corresponding to what an observer is looking straight at. This region is populated almost entirely with cones, while the peripheral region has increasing numbers of rods. Cones have a sensitivity peaking in the yellow and corresponding to the eye response curve.
back to top

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.
back to top

-G-

Glare
Visual discomfort caused by excessive brightness is called discomfort glare. If task performance is affected it is called disability glare. Glare can be direct glare or indirect (reflected) glare.
back to top

-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.
back to top

High-Bay Lighting
Lighting designed for (typically) industrial locations with a ceiling height of 25 feet and above.
back to top

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.
back to top

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.
back to top

Hot Restart Time
Time it takes for a High Intensity Discharge lamp to reach 90% of light output after going from on to off to on.
back to top

-I-

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.
back to top

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.
back to top

Illuminance Meter
A device that measures the illuminance at a location calibrated either in footcandles or in lux. Also know as a light meter.
back to top

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.
back to top

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.
back to top

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.
back to top

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.
back to top

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 ballast. Slimline fluorescent lamps operate only on instant start circuits.
back to top

Integral
A popular term for a compact fluorescent lamp which includes a built-in ballast.
back to top

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.
back to top

Isocandela Plot
A plot with lines connecting points of equal luminous intensity around a source.
back to top

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.
back to top

-J-

back to top

-K-

Kelvin
A unit of temperature starting from absolute zero, parallel to the Celsius (or Centigrade) scale. 0C is 273K.
back to top

Kilowatt (kW)
The measure of electrical power equal to 1000 watts.
back to top

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)
back to top

-L-

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.
back to top

Lamp Height
Referenced by IEC as Dimension C. Also referred to as "Base Face to Top of Lamp".
back to top

Lamp Types
Filament lamps: Incandescent and Halogen..
Discharge Lamps: Fluorescent, HID (High Intensity Discharge)
HID Lamps: Mercury, HPS (High Pressure Sodium), and MH (Metal Halide).
back to top

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.
back to top

Light
Radiant energy that can be sensed or seen by the human eye. Visible light is measured in lumens.
back to top

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.
back to top

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.
back to top

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.
back to top

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.
back to top

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.
back to top

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.
back to top

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.
back to top

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.
back to top

Luminaire Efficiency
The ratio of total lumens emitted by a luminaire to those emitted by the lamp or lamps used in that luminaire.
back to top

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.
back to top

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."
back to top

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.
back to top

-M-

Maximum Overall Length (M.O.L.)
The end-to-end measurement of a lamp, expressed in inches or millimeters.
back to top

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.
back to top

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.
back to top

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.
back to top

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.
back to top

Mesopic
Typically referring to nighttime outdoor lighting conditions, the region between photopic and scotopic vision.
back to top

Mogul Base
A screw base used on larger lamps that is bigger than a standard medium base.
back to top

Monochromatic Light
Light with only one wavelength (i.e. color) present.
back to top

Mounting Height
Distance from the bottom of the fixture to either the floor or work plane, depending on usage.
back to top

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.
back to top

-N-

National Stock Number
The standardized part number used by the US Government for procurement.
back to top

Nanometer
A unit of wavelength equal to one billionth of a meter.
back to top

-O-

Open Circuit Voltage (OCV)
Open Circuit Voltage measured across the socket the lamp screws into, with the ballast powered on. It is dangerous to stick a voltmeter into such a socket without precise knowledge of the ballast because exceedingly high voltages could be present.
back to top

Open Fixture Rated
Lamps that are approved for burning in open fixtures (as opposed to enclosed fixtures which have an acrylic lens or plate glass enclosure).
back to top

Operating Position or Burn Position
Mercury and High Pressure Sodium lamps may be operated in any burn position and will still maintain their rated performance specifications. Metal Halide and Low Pressure Sodium lamps, however, are optimized for performance in specific burn positions, or may be restricted to certain burn positions for safety reasons.
back to top

Operating Voltage
For electrical discharge lamps, this is the voltage measured across the discharge when the lamp is operating. It is governed by the contents of the chamber and is somewhat independent of the ballast and other external factors.
back to top

-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.
back to top

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.
back to top

Photometry
The measurement of light and related quantities.
back to top

Photopic
Vision for which the cones in the eye are responsible; typically at high brightness and in the foveal or central region.
back to top

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.
back to top

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.
back to top

Pulse Start
An HID ballast with a high voltage ignitor to start the lamp.
back to top

-Q-

Quartz
A name for fused silica or melted sand from which many high-temperature containers are fashioned in the lighting industry. Quartz looks like glass but can withstand the high temperatures needed to contain high intensity arc discharges.
back to top

-R-

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.
back to top

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.
back to top

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.
back to top

Reflectance
The ratio of light reflected from a surface to that incident upon it.
back to top

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.
back to top

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.
back to top

-S-

Scotopic
Vision where the rods of the retina are exclusively responsible for seeing, typically like the light levels in the countryside on a moonless, starlit night.
back to top

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 (scotopic vision) and cones to yellow light (photopic vision). The scotopic/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.
back to top

Seal Temperature (Maximum)
The maximum operating temperature of the seal of the lamp in Celsius.
back to top

Self-Ballasted Lamps
A discharge lamp with an integral ballasting device allowing the lamp to be directly connected to a socket providing line voltage.
back to top

Source Size
For Projection lamps, this is defined as the dimensions of the rectangular area, centered on the lamp axis, within which all luminous parts of the filament lie, when viewed perpendicular to the axis of the filament coil or to the plane of C-13 and C-13D filaments.
back to top

Spacing to Mounting Height Ratio
Ratio of fixture spacing (distance apart) to mounting height above the work plane; sometimes called spacing criterion. It is OK to have fixture spaced closer than the spacing criterion suggested by the manufacturer but not farther, or you will get dark spots in-between fixtures.
back to top

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.
back to top

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.
back to top

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.
back to top

Specular Reflection
Reflection from a smooth, shiny surface, as opposed to diffuse reflection.
back to top

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.
back to top

Starter
An electronic module or device used to assist in starting a discharge lamp, typically by providing a high-voltage surge.
back to top

Starting Temperature (Minimum)
The minimum ambient temperature at which the lamp will start reliably.
back to top

System
A term referring to the lamp and ballast combination, and sometimes to the entire lighting delivery system including the fixture, the optics, the particular layout and the lighting controls.
back to top

-T-

Task Lighting
Supplemental lighting provided to assist in performing a localized task, e.g. a table lamp for reading or an inspection lamp for fabric inspection.
back to top

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 groundwater.
back to top

Terminal to Terminal Starting Lamp Voltage (VRMS) (Minimum or Maximum)
The minimum or maximum allowed voltage allowed into lamp from ballast under varying conditions as specified.
back to top

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.
back to top

Troffer
A long, recessed lighting unit, usually installed in an opening in the ceiling.
back to top

-U-

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.
back to top

Uniform Product Code (UPC)
The 12 digit code on the saleable unit that is used for scanning at the register.
back to top

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).
back to top

-V-

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.
back to top

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.
back to top

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.
back to top

Visual Task
The task associated with seeing; objects and details that must be seen to perform an activity.
back to top

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.
back to top

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.
back to top

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.)
back to top

-W-

Wall Temperature (Maximum Bulb)
The maximum operating bulb wall temperature in Celsius.
back to top

Warm Up Time to 90%
The time it takes for a High Intensity Discharge lamp to reach 90% of light output after being turned on.
back to top

Warm White
Refers to a color temperature around 3000K, providing a yellowish-white light.
back to top

Watt
A unit of electrical power. Lamps are rated in watts to indicate the rate at which they consume energy.
back to top

Wattage Indicator Reduced
Indicates that this is a reduced wattage option for lamps normally used in this application. Be sure to check wattage, lumens and life to determine which lamp is best suited to your needs.
back to top

Wavelength
The distance between two neighboring crests of a traveling wave. The wavelength of light is between 400 and 700 nanometers.
back to top

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.
back to top

-X-
back to top

-Y-
back to top

-Z-
back to top