Current which flows in one direction and then the other, alternately.
Adaptation
The process by which the human eye adjusts to a change in light level.
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).
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.
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.)
Ballast An auxiliary piece of equipment required to start and to properly control the flow of current to gas discharge light sources such as fluorescent and high intensity discharge (HID) lamps. Typically, magnetic ballasts (also called electromagnetic ballasts) contain copper windings on an iron core while electronic ballasts are smaller and more efficient and contain electronic components.
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. Sample Base Types
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. BayonetA 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 encompassing the central part of the beam out to the angle where the intensity is 50% of maximum.
Beam Lumens 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.
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. Black Light A popular term referring to a light source emitting mostly near UV (320 to 400 nm) and very little visible light.
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.
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. BrightnessBrightness can refer to any of several technical terms used in lighting and is, therefore, ambiguous
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.
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.
Capacitor
Device in ballast that stores electrical energy. Often used for power factor correction and lamp regulation.
Ceramic Metal Halide (CMH®)
A type of metal halide lamp that uses a ceramic material for the arc tube instead of glass quartz, resulting in better color rendering (>80 CRI) and improved lumen maintenance.
Chromaticity
Measure to identify the color of a light source, typically expressed as (x,y) coordinates on a chromaticity chart.
Coil
Windings of copper or aluminum wire surrounding the steel core in ballast. Also refers to the entire assembly comprising the inductor or transformer.
Core
Component of electromagnetic ballast that is surrounded by the coil. Core is comprised of steel laminations or solid ferrite material.
covRguard®
A special plastic shielding on the outside of tubular fluorescent lamps that effectively contains shattered glass particles if the lamp is broken. Such protection is mandated in many industries and locations, e.g. food packaging.
Daylight Harvesting
Lighting design for building interiors that makes of daylight as a way of reducing energy consumption.
Daylight Lamp
A lamp resembling the color of daylight.
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.
Electrode
Any metal terminal emitting or collecting charged particles, typically inside the chamber of a gas discharge lamp.
Electrodeless Lamps
Light sources where the discharge occurs in a chamber with no electrodes.
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.
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.
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.
Fluorescent Lamp
A high efficiency lamp utilizing an electric discharge through inert gas and low pressure mercury vapor to produce ultraviolet (UV) energy.
Foot Candles
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.
Fovea, Foveal Vision
A small region of the retina corresponding to what an observer is looking straight at.
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.
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.
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.
Hertz (Hz)
Unit used to measure frequency of alteration of current or voltage.
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.
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.
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. Integral
A popular term for a compact fluorescent lamp which includes a built-in ballast (See CFL). 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 on a surface illuminated by a source or sources.
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.
Light
Radiant energy that can be sensed or seen by the human eye. Visible light is measured in lumens.
Current which flows in one direction and then the other, alternately.
Adaptation
The process by which the human eye adjusts to a change in light level.
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).
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.
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.)
Ballast
An auxiliary piece of equipment required to start and to properly control the flow of current to gas discharge light sources such as fluorescent and high intensity discharge (HID) lamps. Typically, magnetic ballasts (also called electromagnetic ballasts) contain copper windings on an iron core while electronic ballasts are smaller and more efficient and contain electronic components.
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. Sample Base Types
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.
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 encompassing the central part of the beam out to the angle where the intensity is 50% of maximum.
Beam Lumens
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.
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.
Black Light
A popular term referring to a light source emitting mostly near UV (320 to 400 nm) and very little visible light.
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.
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 Brightness can refer to any of several technical terms used in lighting and is, therefore, ambiguous
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.
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.
Capacitor
Device in ballast that stores electrical energy. Often used for power factor correction and lamp regulation.
Ceramic Metal Halide (CMH®)
A type of metal halide lamp that uses a ceramic material for the arc tube instead of glass quartz, resulting in better color rendering (>80 CRI) and improved lumen maintenance.
Chromaticity
Measure to identify the color of a light source, typically expressed as (x,y) coordinates on a chromaticity chart.
Coil
Windings of copper or aluminum wire surrounding the steel core in ballast. Also refers to the entire assembly comprising the inductor or transformer.
Core
Component of electromagnetic ballast that is surrounded by the coil. Core is comprised of steel laminations or solid ferrite material.
covRguard®
A special plastic shielding on the outside of tubular fluorescent lamps that effectively contains shattered glass particles if the lamp is broken. Such protection is mandated in many industries and locations, e.g. food packaging.
Daylight Harvesting
Lighting design for building interiors that makes of daylight as a way of reducing energy consumption.
Daylight Lamp
A lamp resembling the color of daylight.
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.
Electrode
Any metal terminal emitting or collecting charged particles, typically inside the chamber of a gas discharge lamp.
Electrodeless Lamps
Light sources where the discharge occurs in a chamber with no electrodes.
Elliptical Reflector (ER) Lamp
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.
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.
Fluorescent Lamp
A high efficiency lamp utilizing an electric discharge through inert gas and low pressure mercury vapor to produce ultraviolet (UV) energy.
Foot Candles
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.
Fovea, Foveal Vision
A small region of the retina corresponding to what an observer is looking straight at.
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.
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.
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.
Hertz (Hz)
Unit used to measure frequency of alteration of current or voltage.
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.
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.
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.
Integral
A popular term for a compact fluorescent lamp which includes a built-in ballast (See CFL).
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 on a surface illuminated by a source or sources.
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.
Light
Radiant energy that can be sensed or seen by the human eye. Visible light is measured in lumens.