Lusio 101 Glossary
Use this glossary as a quick reference on the many terms associated with high bay lighting, low bay lighting, LEDs, and lighting applications in general. Click through the alphabetical entries (A-Z) by clicking on a starting letter:
Click a letter to start
AC (Alternating Current)
Current which flows in one direction and then the other, alternately.
Directional lighting to emphasize a particular object or draw attention to a display item.
The process by which the human eye adjusts to a change in light level.
The general lighting present in an area -- excluding task lighting and accent lighting but including general lighting and daylight streaming in.
The standard unit of measurement for electric current that is equal to one coulomb per second. It defines the quantity of electrons moving past a given point in a circuit during a specific period. “Amp” is an abbreviation. Watts (power) = Volts x Amps (current).
ANSI (American National Standards Institute)
A consensus-based organization which coordinates voluntary standards for the physical, electrical and performance characteristics of lamps, ballasts, luminaires and other lighting and electrical equipment.
ANSI Ballast Type
Ballast type used to operate lamp in accordance with ASNI standard.
Three 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.
Also called "lighting application," it refers to the particular use the lamp is being put to as in high bay industrial applications or retail lighting applications. The term can also refer in a general way to "application engineering" which deals with specific parameters and usage of light sources.
Intense luminous discharge formed by the passage of electric current in a gaseous medium across a space between electrodes.
A light source containing an arc. Also called a discharge lamp, or an arc discharge lamp.
In High Intensity Discharge lamps this is the distance between the electrode tips, which represents the physical length of the electrical discharge.
American Society of Heating, Refrigerating and Air-Conditioning Engineers
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.
A single opaque or translucent element used to control light distribution at certain angles.
A device used to operate fluorescent and HID lamps. The ballast provides the necessary starting voltage, while limiting and regulating the lamp current during operation.
Intermittent operation due to high temperature condition of the ballast or ambient temperature, which causes the thermal protector to open and turn off the ballast. After cooling down, the thermal protector closes, turning on the ballast and starts the heating cycle over again.
Ballast Efficacy Factor (BEF)
Defined as ballast factor divided by input watts. The value is used to evaluate various lighting systems based on light output and power input. The BEF can only be used to compare systems operating the same type and quantity of lamps.
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. Note that the "rated output" is sometimes measured on a reference ballast unlike ones that actually operate the lamp in the field. A ballast with a ballast factor of 0.94 will result in the lamp's emitting 94% of its rated lumen output. A ballast with a lower BF results in less light output and also generally consumes less power.
Sound generated by the vibration of laminations in the iron core of the transformer or inductor present in the ballast.
Power or energy dissipated in the ballast as heat and not converted to lamp energy.
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.
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.
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 is sometimes called beam spread.
The total lumens present within the portion of the beam contained in the beam angle.
Beam Spread (Approximate)
For reflector type lamps. 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.
Control of light source intensity at two discrete levels in addition to off.
Bottom Exit (BE)
(LFL plug-in ballasts) 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 onto a junction box plate.
A loose way of referring to a lamp. "Bulb" refers to the outer glass bulb containing the light source.
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.
Brightness can refer to any of several technical terms used in lighting and is, therefore, ambiguous.
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 (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.
Device in ballast that stores electrical energy. Often used for power factor correction and lamp regulation.
Metal filaments that emit electrons in a fluorescent lamp. Negatively charged free electrons emitted by the cathode are attracted to the positive electrode (anode), creating an electric current between the electrodes.
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).
Center Beam Candlepower (CBCP)
Refers to the luminous intensity at the center of the beam of a blown or pressed reflector lamp. Measured in candelas.
Measure to identify the color of a light source, typically expressed as (x,y) coordinates on a chromaticity chart.
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.
Designates a ballast meets or exceeds the requirements of Public Law 100-357 establishing standards of efficiency.
Class P Thermal Protector
A switching device sensitive to current and heat that automatically disconnects ballast if the temperature exceeds UL temperature limitations.
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.
Windings of copper or aluminum wire surrounding the steel core in ballast. Also refers to the entire assembly comprising the inductor or transformer.
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.
Color Rendering Indicator
Draws attention to the fact that this is a lamp with high color rendering, which helps objects and persons illuminated to appear more true to life.
Color Temperature (Correlated Color Temperature-CCT)
The color temperature is a specification of the color appearance of a light source, relating the color to a reference source heated to a particular temperature, measured by the thermal unit Kelvin. The measurement can also be described as the "warmth" or "coolness" of a light source. Generally, sources below 3200K are considered "warm;" while those above 4000K are considered "cool" sources.
Compact Fluorescent 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 candelabra screw bases for easy replacement of incandescent lamps.
A term loosely used to denote a color temperature of around 4100 K.
Component of electromagnetic ballast that is surrounded by the coil. Core is comprised of steel laminations or solid ferrite material.
An illuminance meter that measures the light level correctly irrespective of the angle the light is coming from.
Cost of Light
Usually refers to the cost of operating and maintaining a lighting system on an ongoing basis.
Crest Factor (Lamp Current Crest Factor)
Ratio of peak to RMS for any AC waveform. Crest factor can refer to voltage crest factor or current crest factor.
Current Type (AC/DC)
Whether the operational voltage is based on Alternating Current or Direct Current.
Lighting design for building interiors that makes of daylight as a way of reducing energy consumption.
An electrical current flowing in one direction only.
Dichroic Reflector (or Filter)
A reflector (or filter) that reflects one region of the spectrum while allowing the other region(s) to pass through. A reflector lamp with a dichroic reflector will have a "cool beam" i.e. most of the heat has been removed from the beam by allowing it to pass through the reflector while the light has been reflected.
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.
A device that produces light by using an electric arc, rather than a filament, to create illumination.
Glare producing discomfort. It does not necessarily interfere with visual performance or visibility.
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.
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.
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.
Electrical Testing Laboratory (ETL)
Independent testing laboratory that performs ballast tests and certifies accuracy of performance data.
Any metal terminal emitting or collecting charged particles, typically inside the chamber of a gas discharge lamp. In a fluorescent lamp, the electrodes are typically metal filaments coated with special powders called emission mix. Negatively charged free electrons emitted by one electrode are attracted to the positive electrode (anode), creating an electric current and arc between electrodes.
Electromagnetic Ballast (Magnetic Ballast)
A ballast used with discharge lamps that consists primarily of transformer-like copper windings on a steel or iron core.
EMI (Electromagnetic Inference)
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 (Federal Communications Commission) compliant.
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.
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.
The electrode in a transistor where electrons originate.
A measure of work done by an electrical system over a given period of time. Expressed as Kilowatt-hours (kWh).
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
An Energy Service Company (ESCO) is a commercial business providing a broad range of comprehensive energy solutions including designs and implementation of energy savings projects, energy conservation, energy infrastructure outsourcing, power generation and energy supply, and risk management.
Essentials Bay Series Fixtures
Lusio Essentials Bay Series fixtures High lumen output commercial and industrial LED fixtures economically designed housings for cost-conscious applications. Fixtures deliver high efficacies (lumens per watt), wide distributions and excellent fixture-to-fixture spacing and crossover.
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.
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.
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.
Metal tungsten wire heated by the passage of electrical current, used to emit light in incandescent lamps. In fluorescent lamps the filament is coated with emission mix and emits electrons when heated.
The periodic variation in light level caused by AC operation that can lead to strobe effects.
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")
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.
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."
A high efficiency lamp utilizing an electric discharge through inert gas and 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.
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.
Four-Pin Compact Fluorescent Lamps
A "plug-in" compact fluorescent lamp with 4 pins in the base to make electrical contact with the ballast.
Rate of alternation in an AC current. Expressed in cycles per second or Hertz (Hz).
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.
Designed to provide a substantially uniform illuminance throughout an area, exclusive of any provision for special local requirements.
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.
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.
An integral multiple of the fundamental frequency (60 Hz) that becomes a component of the current.
Unit used to measure frequency of alteration of current or voltage.
Lighting designed for commercial and industrial locations.
High Efficiency (Energy Saving) Electromagnetic Ballast
Ballast with core & coils, designed to minimize ballast losses compared to the "standard" ballast.
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 mercury and various gases with other chemicals and operate at relatively high pressures and temperatures.
High Power Factor
A ballast whose power factor is corrected to 90% or greater by the use of a capacitor.
High-Pressure Sodium (HPS) Lamp
HPS lamps are high intensity discharge light sources that product light by an electrical discharge though sodium vapor operating at relatively high pressures and temperatures.
Hot Restart Time
Time it takes for a High Intensity Discharge lamp to reach 90% of light output after going from on to off to on.
IES stands for Illuminating Engineering Society. IES standard file format was created for the electronic transfer of photometric data over the web. It has been widely used by many lighting manufacturers and is one of the industry standards in photometric data distribution. An IES file is basically the measurement of distribution of light (intensity) stored in ASCII format.
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.
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.
A device that measures the illuminance at a location calibrated either in footcandles or in lux.
Emission of visible light by a heated material.
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.
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.
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.
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.
The measure of the amount of light a lamp produces after it has been operating 100 hours.
Power supply voltage required for proper operation of fluorescent or HID ballast.
The total power input to the ballast which includes lamp watts and ballast losses. The total power input to the fixture is the input watts to the ballast or ballasts and is the value to be used when calculating cost of energy and air conditioning loads.
Lamp starting method in which lamps are started by high voltage input with no preheating of lamp filaments. Some rapid start lamps are designed so that they may be instant started.
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.
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.
There currently are no entries in our glossary for words that begin with J.
A unit of temperature starting from absolute zero, parallel to the Celsius (or Centigrade) scale. 0C is 273K.
1,000 Hertz (cycles per second).
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.
Layers of steel, making up the "core" that is surrounded by the coils in a core & coil ballast.
The term used to refer to the complete light source package, including the inner parts as well a the outer bulb or tube.
Lamp Current Crest Factor
Ratio of peak lamp current to RMS or average lamp operating current.
Lamp Rated Life
The number of operating hours at which half of a large group of product samples are expected to fail. The rated life is a median value of life expectancy; individual lamp life may vary considerably from the published rated life and operating conditions (e.g., temperature, hours per start) may affect actual life because rated life is based on standard test conditions. In addition, the way a product fails can vary by technology. For example, incandescent lamps abruptly stop producing any light while LEDs are considered to have failed when their light output drops below a certain fraction of the initial level.
Input power used to operate lamps.
A transparent or semi-transparent element which controls the distribution of light by redirecting individual rays. Luminaires often have lenses in addition to reflectors.
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.
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 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.
A measure of the luminous flux or quantity of light emitted by a source.
A ratio expressing the luminous efficacy of a light source.
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. Also called Lumen Depreciation.
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.
The ratio of total lumens emitted by a luminaire to those emitted by the lamp or lamps used in that luminaire.
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).
The time rate of flow of light.
Innovative LED fixtures for use in warehouse, laboratories, cold storage facilities, high ceiling office spaces, manufacturing facilities, retail and showroom areas, convention centers, and many other commercial and industrial applications. Instead of mimicking previous fluorescent and HID forms, Lusio® fixtures are completely original and unique designs that maximize the optics, heat management, and lifetimes of rigorously tested LEDs. As a result, Lusio® specific offerings for high bay lighting, low bay lighting, and aisle lighting applications deliver low glare, highly energy efficient lighting with lumens that meet or exceed traditional legacy fluorescent and metal halide lighting sources.
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.
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.
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
Metal Halide Lamp
A high-intensity discharge (HID) lamp that uses mercury and several halide additives as light-producing elements.
A screw base used on larger lamps, e.g. many HID lamps.
Light with only one wavelength (color) present.
Distance from the bottom of the fixture to either the floor or work plane, depending on usage.
A unit of wavelength equal to one billionth of a meter.
Abbreviation for National Electrical Manufacturers Association.
Capacitor used in ballasts to help provide power factor correction. Contains no polychlorinated biphenyls and meets EPA requirements.
Control device that turns lights off after the space becomes unoccupied. May be ultrasonic, infrared or other type.
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.
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).
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.
A term referring to the components of a light fixture (such as reflectors, refractors, lenses, louvers) or to the light emitting or light-controlling performance of a fixture.
Parallel Lamp Operation
Refers to ballasts that employ multiple output current paths from a single ballast to allow lamps to operate independent of one another, allowing other lamps operated by the ballast to remain lit should companion lamp(s) fail.
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.
PCB (Polychlorinated Biphenyls)
Chemical pollutant formerly used in ballast capacitors that were part of ballasts. It is now illegal to use PCB's and most such ballasts have been replaced over time.
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.
The measurement of light and related quantities.
A photometric report is a set of printed data describing the light distribution, efficiency, and zonal lumen output of a luminaire. This report is generated from laboratory testing.
Material used to completely surround and cover components of some magnetic and electronic ballasts. Potting compound fulfills functions of protecting components, dampening sound, and dissipating heat.
The rate at which energy is taken from an electrical system or dissipated by a load, expressed in watts (W); power that is generated by a utility is typically expressed in volt-amperes (V-A).
Measurement of the relationship between the AC source voltage and current. Power Factor equals Input Watts divided by the product of Line Volts times Line Amps (Volt Amps or VA).
Power Factor Corrected
Ballasts that incorporate a means of Power Factor Correction but whose power factor is 90% or greater.
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.
A fluorescent lamp in which the filament must be heated by use of a starter before the arc is created. These lamps are typically operated with electromagnetic ballasts.
Pro-Optics Series Fixtures
The Lusio Pro-Optics Series of full-featured commercial and industrial LED fixtures featuring five different light distributions designed to meet applications where glare control and vertical footcandles are important.
An HID ballast with a high voltage ignitor to start the lamp.
Quality of Lighting
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.
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.
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.
Lamp starting method in which lamp filaments are heated while open circuit voltage (OCV) is applied to facilitate lamp ignition.
Rapid Start Lamp
A fluorescent lamp with two pins at each end connected to the filament. The filaments are heated by the ballast to aid in starting.
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.
The time required for a lamp to restrike, or start, and to return to 90% of its initial light output after the lamp is extinguished. Normally, HID lamps need to cool before they can be restarted.
Refers to upgrading a fixture, room, or building by installing new parts or equipment.
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.
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.
Seal Temperature (Maximum)
The maximum operating temperature of the seal of the lamp in Celsius.
A material whose electrical conductivity is between that of a conductor and an insulator; the conductivity of most semiconductors is temperature dependent.
Series Lamp Operation
Refers to ballasts that employ a single current path passing through all lamps operated by the ballast. If one lamp should fail, companion lamps operated by the same ballasts will also extinguish or dim.
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.
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.
Reflection from a smooth, shiny surface, as opposed to diffuse reflection.
Standard Alternating Current Frequency in the United States
60 Hertz (Hz) or 60 cycles per second.
An electronic module or device used to assist in starting a discharge lamp, typically by providing a high-voltage surge.
Starting Temperature (Minimum)
The minimum ambient temperature at which the lamp will start reliably.
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.
Also referred to as relative system efficacy, system efficacy is a measurement of a system's ability to convert electricity into light. Measured in lumens per watt (LPW), system efficacy is the ratio of the light output (in lumens) to the active power (in watts).
T-12, T-8, T-5
A designation for the diameter of a tubular bulb in eighths of an inch; T-12 is 12 eighths of an inch, or 11/2 inches; T-8 is 1 inch, and so on.
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.
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.
High voltage surges through an electrical system caused by lightning strikes to nearby transformers, overhead lines or the ground. May also be caused by switching of motors or compressors, as well as by short circuits or utility system switching. Can lead to premature ballast failure.
Control of light source intensity at three discrete levels in addition to off.
A long, recessed lighting unit, usually installed in an opening in the ceiling.
Two-Pin Compact Fluorescent Lamps
Type of lamps that have the glow bottle starter built into the base of the lamp. Traditionally 2-pin lamps are designed to work with electromagnetic ballasts.
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).
Lighting from light sources on a wall typically above eye level, shielded by horizontal panels. The light may be upward or downward directed.
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.
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 "voltage" of a ballast (e.g. 277 V) refers to the line voltage it must be connected to.
A measurement of the electromotive force in an electrical circuit or device expressed in volts.
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.
Refers to a color temperature around 3000K,providing a yellowish-white light.
A unit of electrical power. Lamps are rated in watts to indicate the rate at which they consume energy.
The distance between two neighboring crests of a traveling wave. The wavelength of light is between 400 and 700 nanometers.
There currently are no entries in our glossary for words that begin with X.
There currently are no entries in our glossary for words that begin with Y.
The direction directly above the luminaire (180 angle).