LED Lighting Glossary |


Accent Lighting: Directional lighting used to emphasise a particular object, a specific location or area.
Alternating Current (AC): The flow of electricity which travels in waves and pulses on and off in cycles many times per second. The number of cycles per second is referred to as frequency. The most common frequency of electricity used in the UK is 50-1000 and in the US is 60 hertz (cycles per second).
Ambient Lighting: Designed to provide general uniform illumination throughout the work area.
Amp: (SEE Ampere) A common abbreviation for Ampere.
Ampere: 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 over a period of time.
Application: This term refers to how a product is used; i.e., a vandal-resistant fixture in a prison is a good “application” of this particular product.
Back Plate: A bracket on a surface or wall mounted luminaire used to fasten the luminaire to the cover of the outlet box.
Baffle: A shield of metal, wood or plastic used to screen a light source from normal angles of viewing. A grooved cylinder dropped below a light source to conceal the lamp and provide light cutoff.
Battery: A chemical device that provides DC (direct current) voltage. It is a source of electrical energy.
Breaker: An electromechanical device that acts as a switch-and- fuse combination to protect and disconnect a circuit in case of an overload or short circuit

Candela: Unit of luminous intensity, describing the intensity of a light source in a specified direction.
Candlepower: Older terminology for luminous intensity; the intensity in candelas of light from a source.
Capacity: The allowable volume of amperage for a feeder at its particular current carrying capacity. Each conductor is sized, giving it a certain capacity to feed current to a load.
CAT-5: Twisted pair cable.
CE Mark: CE compliant, this means that the product is certified to meet the EU safety requirements.
Circuit: A completed path of electrical elements including the electric source, the wiring and the load.
Compact Fluorescent: Twin-tube fluorescent lamp used in some emergency lighting, down lighting, and Fluorescent products. The lamp life is about 10 times that of incandescent lamps and uses less power.
Conductor: A substance or material (typically wire) capable of carrying electric current.
Conduit: A metal tube or “pipe” used as an enclosure to protect electrical conductors; also a type of electrical raceway.
Constant Current: A constant electrical current to a product but the voltage may vary. The product will not be able to be dimmed and there may be the possibility that a power surge could damage some products.
Constant Voltage: A constant voltage will be supplied to a product whatever the current is required. This will protect against power surges.
Cord Set: (Fig 8 lead) Electrical cord with attachment plug which is built into the fixture so that it may be plugged into a standard electrical outlet.
Coulomb: A unit of electrical charge equal to 6.24 x 10 (to the 18th power) electrons.
Current: The flow of electrons in an electrical circuit (measured in amperes)

Die-Cast: A metal molding process where hot molten metal is injected into a “hard” mold. After the molten metal hardens and cools, it is removed and trimmed to complete the finished part
Diffuse: Term describing the lack of directionality in light distribution. Refers to the scattering of light.
Digital Dimmer: Dimmer controlled directly by a series of computer generated digital signals.
Dimmer: A device which changes lighting intensity by regulating electrical power delivered to the lamp.
Dimming: see separate article on dimming LEDs
Direct Current (DC): Flow of continuous electricity in one direction from positive to negative.
Direct/Indirect Lighting: A variant of general diffuse lighting in which the luminaries emit little or no light at angles near the horizontal.
Directional Lighting: Lighting provided on the work-plane or on an object predominately from a particular direction.
Discharge: The removal of stored energy in a battery.
DMX: DMX512 is a communications protocol that is most commonly used to control stage lighting and effects.
Down light: A type of point source ceiling luminaire, usually fully recessed. May feature an open reflector or may incorporate a shielding or directing device.
Dual Circuit: Refers to a branch circuit configuration in which two hot conductors are used with one or two neutral conductors as a grounding conductor to form a circuit.
Dual Circuit Switching: Two circuits in one area that are switched to a given level.
Dual Voltage: A fixture or product having the capability to operate by either 240 or 110 voltage. A fixture or product having the capability to operate at two differing supply voltages.

Efficacy: A metric used to compare light output to energy consumption. Efficacy is a ratio of lumens to watts and can be defined for bare lamps or for luminaries.
Efficiency: The ratio of the lumen output of the luminaire to that of the bare lamp.
Energy-Saving Lamp: A type of lamp designed to operate more efficiently, producing more lumens per watt than standard lamps, and thus operates at a lower wattage than a standard lamp ie; LED

Five Pin XLR: DMX Connector
Facade Lighting: This term typically refers to the exterior of a building and the lighting of the vertical building surface. This is usually accomplished with floodlights or spotlights or ground mounted landscape luminaries.
Fade Rate: Time required for a dimmer to change from one intensity level to another. Fade rates may be either user adjustable or factory set. Normally used with PRESET SCENE control.
FC: The English unit of measurement of the luminance onto a surface. One foot-candle is equal to one lumen per square foot.
Fixture Schedule: A construction document that lists all luminaries used on a particular job. The list typically includes fixture, type, fixture catalog number, fixture quantity, lamp type, lamp catalog number, ballast type and voltage. (Also known as luminaire schedule).
Flange: Overlapping metal portion of a recessed luminaire at the ceiling line. It serves to trim the ceiling opening around the luminaries.
Fluorescent: A linear light source consisting of a tube filled with gas. When electrical current is applied, the resulting arc emits ultraviolet light that excites the phosphors on the inside of the lamp wall, causing them to radiate visible light.
Foot-lambert (FL): Unit used in lighting to describe the luminance of an area. Today, it is more common to use candelas per meter squared (Candela/meters squared). This term is still occasionally referred to as foot lamberts. 1 fL = 0.3183 (1/pi) cd/feet squared.
Fuse: An electrical safety device, made of wire or thin metal, and usually enclosed in glass, that will melt and “break” the circuit in the event of a current overload.

General Diffuse Lighting: Lighting from luminaries that distribute 40% to 60% of its emitted lumens downward and the balance upward.
General Lighting: Lighting designed to provide essentially uniform illumination throughout the work area exclusive of any provision for any special, localised requirements.
Glare: The effect of brightness or brightness differences within the visual field sufficiently high to cause annoyance, discomfort or loss of visual performance.
Grazing: Down lighting or up lighting indoor or outdoor application used to show texture on surfaces, walls and fabrics.

Halogen: Gas used in tungsten-halogen lamps which increases lamp life and enhances lumen output.
Housing: The body of a light fixture.

Illuminance: A photometric term which quantifies light striking a surface or plane at a point. It is expressed either in lumens per square foot, foot-candles (the English metric) or lumens per square meter, lux (the metric unit). 1 foot-candle = 10.76 lux.
Indirect Lighting: Lighting by luminaries that distribute 90 to 100% of the emitted light upward.
Initial Lumens: The lumen output of a lamp after about 100 hours of operation.
Insulator: A substance or material (such as rubber or glass) that will not permit the flow of electric current.
Integrating Photometer: A device for measuring the total output (luminous flux) of a source with a single measurement.
Intensity: The luminous flux per unit solid angle in a particular direction; may be expressed in candela or lumens per steradian.
Inverter: An electrical circuit that changes direct current (D.C.) to alternating current (A.C.) or vice-versa.
IP (Ingress Protection): The IEC (International Electrotechnical Commission) uses the term “Ingress Protection” or IP to define the environmental protection of an enclosure. This is described in IEC Standard 529. The IP classification system designates by means of a two digit number, the degree of protection against ingress of dust and moisture. The first digit defines the level of protection against solid objects, while the second digit defines the level of protection against moisture. The higher the digit, the greater is the level of protection.

J-Box: Jargon for junction box. A code-approved steel or plastic enclosure in which several wires come together for connection, such as the taps for fixtures.
J Box: An enclosure where conductors or wires are spliced or terminated.

Kelvin: A measurement of temperature. 1o F = 256o Kelvin. 1o C = 274o Kelvin. Used to measure color temperature.

L.E.D.: Light-Emitting Diode.
L.L.D.: The fractional remainder of lamp lumens lost, at rated operating conditions, due to lamp degradation. Mean lumen output divided by initial output.
L.V.D.: Protection feature in an emergency lighting unit in which the load is automatically disconnected when battery voltage drops to a critical point.
Lambertian Surface: A surface that emits, reflects or transmits light according to Lamberts cosine law; i.e. the surface has the same luminance regardless of the viewing angle.
Lamp: The actual source of light in a fixture. Some people refer to fluorescent lamps as “tubes” and incandescent lamps as “light bulbs”.
Lamp Efficacy: A metric used to compare light output to energy consumption. It is the ratio of lumens per watt.
Lamp Life: The number of burning hours at which 50% of any large group of installed lamps are still operational.
Lamp Lumen Depreciation Factor (LLD): The fractional remainder of lamp lumens lost, at rated operating conditions, due to lamp degradation. Mean lumen output divided by initial output.
Lens: Transparent or translucent medium which alters the directional characteristics of light passing through it. Usually made of glass or plastic.
Light Measurement: Generally light sources emit in all directions in the space around them, so in order to able to quantify and measure the emission, an SI unit of solid angle was defined. This takes the form of a cone emanating from a point on the surface of a sphere and this unit of solid angle is called a Steradian.
Lighting Specifier: A person (architect, engineer, lighting designer, owner, etc.) who specifies the lighting equipment for an installation.
Low Voltage Lamp: A lamp that provides both intensity and good colour rendition. Lamp operates at 12V and requires the use of a transformer. Popular lamps are MR16 and PAR36.
Lumen (lm): A measurement of the light output of a lamp, or the SI unit of luminous flux. Photometrically, it represents the luminous output of a source with a uniform emittance of 1 candela over a unit solid angle of 1 steradian.
Luminaire: A complete lighting unit consisting of a lamp or lamps, the parts designed to distribute the light (housing), and any necessary starting components (ballast, socket, etc.).
Luminance: This is the ratio of the luminous intensity to the area of the source and measures the density of luminous intensity. It is defined as Candelas per metre square ad is the only light measurement which can adequately define the brightness of an object.
Luminous Flux: This is defined as the total amount of light energy radiated by a source into the space surrounding it and is measured in lumens.
Luminous Intensity: This is defined as the amount of luminous flux (or energy) emitted from a point souce in a perpendicular direction and is measured in Candelas. Candelas (cd) or millicandela’s (mcd) are generally used to measure the outputs of individual LEDs.
Lux (LX): The metric unit of measurement of the luminance of a surface. One lux is equal to one lumen per square meter.



Occupancy Sensor: Control device that acts as a light switch upon sensing that a person has entered a space. May be ultrasonic, infrared or other type.
Ohm: The standard unit of measurement for electrical resistance in a circuit.
Optics: A term referring to the components of a light fixture (such as reflectors, refractors, lenses, louvers, etc.); also the light-emitting or light-controlling performance of a fixture.
Over current: A protective device for a branch circuit that prevents damage to the circuit due to a current surge or an overload; usually a fuse or a breaker.

PAR Lamp: A Parabolic Aluminised Reflector Lamp. An incandescent or low voltage lamp used to redirect light from the filament in a manner resembling a parabolic reflector. Lamps are available with flood or spot distributions.
Performance Specification: A job specification in which the engineer has directed the electrical contractor to furnish and install lighting equipment that meets a detailed and precise set of performance parameters. These may include photometric, electrical, mechanical, and appearance aspects; a broader directive to the contractor as to the engineer’s intent compared to a Prescriptive Specification.
Perimeter Lighting: Directs light at the edges of an area. Can be used to eliminate weak spots from general lighting.
Photometer: A device for measuring photometric quantities such as luminous intensity, luminance, illuminance and/or luminous flux.
Plenum: 1) Space between the structural ceiling and the finished ceiling. It is the service area concealing the housing part of a recessed fixture.
Power Surge: A sudden surge of high voltage on a power distribution circuit, usually caused by lightning or the switching on/off of heavy loads, especially motors.
Preset: Pre-defined instructions for multiple channels on a colour controller.
Prewired: A fixture which has electrical wires attached to it at the factory to make the installation of the fixture easier and faster.
Prismex: Panel of acrylic, printed with surface dots which get larger towards the centre to give an even coverage of light.

RJ-45: DMX connector for fixed installations.
Radiant Flux: The unit of radiant flux is the watt(W), which is defined as an emission of 1 Joule of energy per second. The incandescent light bulbs and other types of light source are rated in watts to indicate the power they consume over time. A 100W bulb consumes 100J of energy per second; a 40W bulb consumes 40J per second etc. this does not mean that the bulbs radiate 100W or 40W of light, a popular misconception.
Reflector: The part of a light fixture that shrouds the lamps and directs the light emitted from the lamp.
Refractor: A device used to redirect the light output from a source, primarily by bending the waves of light. (See LENS).
RHOS: All new electrical and electronic equipment must be RHOS compliant – an EU directive regulation implemented on the 1st July, 2006. This restricts the use of certain hazardous substances in electrical and electronic equipment.

Scene: The resulting lighting effect of adjusting several channels of a light control system to desired intensity. May be implemented through either MANUAL CONTROL or PRESET selection.
Short Circuit: A circuit that has extremely low resistance causing the current to become very high. This is often caused by a current carrying wire touching a ground wire. Excessive current will damage a circuit or connected equipment; therefore protection must be included to prevent a short circuit.
Short Circuit Protection: A switch or fuse used to open the circuit when a short is detected.
Specification: The precise written detail of the building contract which accompanies the building plans. It normally includes all requirements of the general contractor and subcontractors to furnish and install the specified materials and equipment using prescribed methods and workmanship.
Specification Sheet (Spec sheet): (ALSO CALLED SUBMITTAL SHEET AND CUT SHEET) Data sheet that shows fixture dimensions, descriptions, options and photometrics. These sheets are submitted through the contractor, engineer and architect to obtain final approval on the specific equipment to be furnished.
Specifier: Usually an Electrical Engineer, Lighting Designer or Architect. This design professional specifies the type of lighting equipment, the layout of the lighting equipment, and the manufacturer of the lighting equipment.
Suspended Ceiling: A grid of connecting bars (“inverted tee” is the most common shape) suspended from the structural ceiling by wires. Acoustical tiles and light fixtures rest on these metal tees.

Task Lighting: Supplements the ambient lighting when specific tasks require higher illumination.
Tempered Glass: A type of glass used for light fixtures which has a higher resistance to breakage than normal glass.
Thermal Protector: A device that protects a ballast from overheating.
Track Lighting: Luminaries attached to a linear track system, used in accent lighting and other general lighting applications. The track can be recessed or suspended.
Transformer: A device designed to transfer energy from one circuit to another by electromagnetic induction. Transformers are typically used to increase (step up) or decrease (step down) the voltage from one circuit to another. Also commonly referred to as power supplies or drivers.
Tungsten Halogen: A tungsten filament incandescent lamp filled with halogen gas, with a lamp envelope made of quartz to withstand the high temperature. This lamp contains a certain proportion of halogens, namely iodine, chlorine, bromine, and fluorine that slows down the evaporation of the tungsten. Also commonly referred to as a quartz lamp.

Ultra Violet (UV): Light that is shorter in wavelength and higher in frequency than visible violet light (literally beyond the violet light).

Volt: The standard unit of measurement for electrical potential. It defines the force or pressure of electricity for the satisfactory operation of an electrical device.
Voltage: The potential difference between two points of an electrical circuit.

Wall Wash: Term used to describe lighting to illuminate vertical surfaces from ceiling to floor without shadows or hot spots. Fixtures used to accomplish this are called wallwashers.
Watt (W): The unit for measuring electrical power. It defines the energy consumed by an electrical device when it is in operation. The energy cost of operating an electrical device is determined by the watts it consumes times the hours of use. It is related to volts and amps by the formula: Volts x Amps = Watts.