LED Lighting Terminology and Definitions

LED Lighting Terminology

LED Lighting Terminology – Understanding the Lighting Industry

Understanding LED lighting terminology and their definitions is essential if one is to become an educated consumer of LED merchandise. ECN’s comprehensive compilation of industry terms helps consumers become familiar with industry language and improves communication with contractors and suppliers.

LED Lighting Terminology – Section A thru D

Alternating Current: an electric current that reverses its direction many times a second at regular intervals, typically used in power supplies.

Amperage (Amp): A measure of electrical current.

Backlight: Light emitted in the direction of the luminaire OPPOSITE from the area intended to be lighted which may create unwanted trespass, usually towards the house side of a street light pole. Backlight is a component of the new TM-15-07 based BUG rating system, which replaces the older cutoff classification system.

BUG: System created by IESNA based on TM-15-07 to rate the amount of light emitted from a luminaire in unwanted directions. The methodology represents a comprehensive system that limits lamp lumens to values appropriate for the lighting zone. The BUG rating system replaces the older IES cutoff classification system.

Beam Angle: The angle, in degrees, between the two opposite directions in which the average intensity is 50% of the center beam intensity as measured in at least two rotational planes, 90° from each other, around and through the beam axis.

Binning: process of grouping LEDs during production so they match the same color sector.

Candela: A measure of luminous intensity, or power emitted by a light source in a particular direction. A common candle emits light with a luminous intensity of roughly one candela.

CFL: Compact Fluorescent Lamp.

Chromaticity: A measure of color quality as reflected in the CIE (International Commission on Illumination) 1931 color chart, which provides x/y coordinates of reds, greens and blues (RGB). The color of white LEDs, as measured in Kelvin (K), is reflected in a narrow strip at the center of the CIE chart where RGB combinations create various shades of white.

Color Quality Scale: An alternative to the unsaturated CRI measurement colors. There are 15 highly saturated colors that are used to compare chromatic discrimination, human preference, and color rendering.

Color Rendering Index (CRI): The measured degree of color shift an object undergoes when illuminated by a light source as compared with the color of those same objects when illuminated by a reference source of comparable color temperature.

Color Vector Graphic (TM-30): Which colors are saturated/desaturated and whether there is a hue shift in any of the 16 color bins.

Correlated Color Temperature (CCT): The absolute temperature of a blackbody whose chromaticity most nearly resembles that of the light source.

Covered Lamp: A lamp with an integral ballast or driver and a translucent envelope over the light source(s).

Cutoff Luminaire: One of the IESNA luminaire classifications that prescribe light distribution metrics intended to avoid light pollution. A cutoff luminaire is one in which the luminous intensity (in candelas) at or above an angle of 90° above nadir does not numerically exceed 2.5% of the luminous flux (in lumens) of the lamp or lamps in the luminaire, and the luminous intensity (in candelas) at or above a vertical angle of 80° above nadir does not numerically exceed 10% of the luminous flux (in lumens) of the lamp or lamps in the luminaire. See full-cutoff luminaire.

Decorative Lamp: A lamp with a candle-like or globe shape envelope.

DesignLights Consortium: a non-profit organization whose mission is to drive efficient lighting by defining quality, facilitating thought leadership, and delivering tools and resources to the lighting market through open dialogue and collaboration.

Dimmable Lamp: A lamp capable of emitting varying levels of light controlled by a dimming device.

Diode: A two-terminal device commonly used as a one-way switch allowing the flow of electric current in one direction (called the forward-biased condition) and blocking the flow of the current in the opposite direction (the reverse-biased condition).

Direct Current: power systems that use only one polarity of voltage or current.

Directional Lighting: lighting that travels in a specific direction. While general lighting provides even, overall illumination, directional lighting highlights a specific object or work surface. It is also usually provided by a stronger light source

Driver: An LED power supply that provides either constant level of current, or a constant level of voltage.

Driver Efficiency: A measure of luminaire efficiency that focuses on the performance of the driver or power supply components. Driver efficiency is the ratio of power delivered from the driver divided by the power required to operate the driver.

LED Lighting Terminology – Section E thru H

ETL Mark (Intertek): The ETL Mark is proof of product compliance to North American safety standards. Authorities Having Jurisdiction(AHJs) and code officials across the US and Canada accept the ETL Listed Mark as proof of product compliance to published industry standards.

Energy Star: Energy Star is a voluntary program launched by the U.S. Environmental Protection Agency and now managed by the EPA and U.S. Department of Energy that helps businesses and individuals save money and protect the environment through superior energy efficiency.

Fixture (Or System) Efficiency: A measure of luminaire efficiency that focuses on the performance of the combined luminaire, including source efficiency, driver efficiency, and optical efficiency. Fixture efficiency reflects the amount of useful light delivered by the luminaire divided by the power required to operate it.

Fitted Target Efficiency (FTE): A system created under the draft Energy Star program for outdoor SSL luminaires used to measure how efficiently a luminaire illuminates its targeted area.

Foot-Candle: A measure of illuminance or light intensity. A foot-candle reflects the amount of illumination the inside surface of a 1-foot radius sphere receives from a point source of one candela in the center of the sphere. A foot-candle is also equal to one lumen per square foot.

Full-Cutoff Luminaire: One of the IESNA luminaire classifications that prescribe light distribution metrics intended to avoid light pollution. A full-cutoff luminaire is one in which the luminous intensity (in candelas) at or above an angle of 90° above nadir is zero, and the luminous intensity (in candelas) at or above a vertical angle of 80° above nadir does not numerically exceed 10% of the luminous flux (in lumens) of the lamp or lamps in the luminaire.

Fully-Rated Life: An achievement by a device or system that provides useful service for as long as the device or system manufacturer projects. For example, white LEDs are commonly marketed with 50,000 hour fully-rated lives, where the end of life is defined by the point at which the LED fails to deliver at least 70% of initial lumen output.

Envelope: A transparent or translucent enclosure over a light source. An envelope can also consist of a reflector with integral front cover.

Fidelity Index: How closely observed light renders colors like the sun, using 99 color samples.

Field Angle: The angle between the two directions for which the intensity is 10% of the maximum intensity as measured in a plane through the nominal beam centerline.

Flicker: Luminous flux modulation made perceptible by the motion of objects or by the motion of the observer’s eye when the observer’s eye is still.

Gallium Nitride (GaN): A type of semiconductor material used in manufacturing blue LEDs and other electronic devices.

Glare: Consists primarily of light emitted at high angles projected from the front and back of the luminaire, which may interfere with ground-level pedestrians and motorists. Glare is a component of the new TM-15-07 based BUG rating system, which replaces the older cutoff classification system.

Gamut Index (TM-30): How saturated or desaturated colors are i.e. color intensity.

Goniophotometer: A photometric device for testing the luminous intensity distribution, efficiency and luminous flux of luminaires.

GU24 Based Integrated Lamp: A lamp unit that integrates the lamp and its ballast. It does not include any replaceable or interchangeable parts and utilizes the ANSI standardized GU24 base type.

Ingress Protection Rating (IP): rating system that defines the ability of a product to operate in various environments. Measurement of the protection an item has against solid objects (dust, sand, dirt, etc.) and liquids. IP rating comprised of 2 numbers. The first number refers to the protection against solid objects (dust, etc.) and the second number refers to protection against liquids.

Heat Dissipation: The intentional transition of thermal energy from a hotter object (such as a sensitive electronic device) to a cooler object. Heat dissipation is achieved with LEDs primarily by mounting them on heat sinks made of high-quality aluminum and other alloys.

Heat Sink: An object that absorbs and dissipates heat from another object using thermal contact (either direct or radiant).

High Intensity Discharge (HID): A type of electrical lamp that produces light by striking an electric arc between tungsten electrodes, which is filled with certain gases and other compounds. HID lamps are a traditional light source that offers relatively high efficiency and long life, but sometimes with undesirable color effects.

High Power LEDs: individual components greater than 0.20 watts (Voltage, nominal * Current, nominal).

High Pressure Sodium (HPS): A popular type of high intensity discharge (HID) lamp offering a relatively warm correlated color temperature (CCT), high levels of efficiency, and long life, but only modest levels of color rendering index (CRI).

LED Lighting Terminology – Section I thru L

Illuminating Engineering Society of North America (IESNA): A non-profit organization that “seeks to improve the lighted environment by bringing together those with lighting knowledge and by translating that knowledge into actions that benefit the public.

Indium Gallium Nitride (InGaN): A type of semiconductor material used in manufacturing blue LEDs and other electronic devices.

Input Power: The power draw in watts of a ballast or driver and a light source system operating in a normal mode, as determined in accordance with 10 CFR 430.

Integrated LED Lamp: An integrated assembly comprised of LED packages (components) or LED arrays (modules), LED driver, ANSI standard base and other optical, thermal, mechanical and electrical components.

Isocandela Diagram: Graphic representation of brightness distribution of a light source.

Kelvin (K): A thermodynamic (absolute) temperature scale, based on a measure of absolute zero – the absence of all thermal energy—at zero K. The Kelvin is described without reference to degrees and is written without a degree symbol.

L70: An abbreviation for 70% of initial lumens levels delivered from an LED, which is a common definition of the useful life of an LED.

Lamp: A generic term for a man-made source created to produce optical radiation. By extension, the term is also used to denote sources that radiate in regions of the spectrum adjacent to the visible.

Lamp Sources: General term for various electric lighting components including incandescent, fluorescent and high intensity discharge (HID) lamps, which are commonly called light bulbs. Although LEDs are sometimes called lamps, the term more frequently refers to traditional lamps.

LED Array or Module: An assembly of LED packages (components) or dies on a printed circuit board or substrate, possibly with optical elements and additional thermal, mechanical, and electrical interfaces that are intended to connect to the load side of a LED driver.

LED Driver Case Temperature Measurement Point (TMPC): A location on an LED driver case, designated by its manufacturer, which will have the highest temperature of any point on the driver case during normal operation.

LED Efficiency: A measure of the light output of an LED device, generally measured in lumens, divided by the power, generally measured in watts, required to operate the device. This relationship, lumens per watt, is a key measure of LED performance.

LED Junction Temperature (TJ): The temperature of the p/n junction inside the LED. Although TJ cannot be directly measured, there are a number of widely-used, reliable methods of accurately estimating TJ .

LED Package: An assembly of one or more LED dies that includes wire bond or other types of electrical connections, possibly with an optical element and thermal, mechanical, and electrical interfaces.

LED Pitch: LED pitch is the distance between the individual chips on a strip (FPCB). The shorter the pitch, the more uniform the light tends to be and the less spotting.

LED Temperature Measurement Point (TMPLED): A location on an LED package/module/array, designated by its manufacturer, which provides a surrogate temperature measurement location for the actual LED junction. The TMPLED may be a solder joint at the board attachment site, a point on the LED package case, or a location on the board of an LED module or array.

Light Emitting Diode (LED): An electronic light source derived from a semiconductor diode possessing unidirectional electric current properties—in other words, diodes are one-way switches. When a voltage is applied in the forward direction, electrons from one side of the p/n junction recombine with holes on the other side of the junction, and energy is released in the form of light.

LM-79: Popular name for an LED measurement standard, the full title of which is IESNA LM-79-08, Approved Method for the Electrical and Photometric Measurements of Solid-State Lighting Products. This standard provides guidelines to photometric labs for the proper and repeatable measurement of LED lighting systems.

LM-80: Popular name for an LED measurement standard, the full title of which is LM-80-08, Approved Method for Measuring Lumen Maintenance of LED Light Sources. This standard provides guidelines to LED manufacturers for measuring lumen maintenance, or the level of light output maintained over predetermined time periods.

Low Pressure Sodium (LPS): A popular type of high intensity discharge (HID) lamp offering an extremely warm correlated color temperature (CCT), very high levels of efficiency, and long life, but very poor levels of color rendering index (CRI).

Lumen Depreciation: A measure of the declining level of lumen output produced by a lamp or luminaire over time.

Lumen Maintenance: A measure of the level of lumen output produced by a lamp or luminaire over time compared to the initial level of lumen output.

Lumen Output: The amount of light produced by a luminaire at a given time.

Lumens Per Watt (LPW): The ratio of light produced by an LED device, measured in lumens, divided by the power, measured in watts, required to operate the device. LPW is a key measure of LED performance.

Luminaire: A lighting fixture complete with lamp, optical components used to direct light, housing, and power supply (e.g., a fluorescent ballast or LED driver).

Luminous Efficacy: calculated by measuring the lumen output and then dividing that number by watts.

Luminous Intensity Distribution Diagram: test that determines the angle of an emitted beam of light.

Lux: A metric measure of illuminance, or the apparent intensity of light hitting or passing through a surface.

LED Lighting Terminology – Section M thru P

MacAdam Color Ellipse: A space around a chromaticity coordinate that sets the boundary at which a given percentage of people are able to determine that two colors, one with chromaticity coordinates at the center of the ellipse, and one with chromaticity coordinates on the ellipse, are just noticeably different.

Mercury Vapor: Historically, popular type of high intensity discharge (HID) lamp offering a relatively warm correlated color temperature (CCT), high levels of efficiency, and long life, but only modest levels of color rendering index (CRI). Due to environmental concerns, most mercury vapor luminaires are no longer available, but mercury vapor lamps remain available for existing luminaires.

Mesopic Vision: A combination of photonic vision and scotopic vision in environments with low, but not completely dark, light levels.

Metal Halide (MH): A popular type of high intensity discharge (HID) lamp offering a relatively cool correlated color temperature (CCT) and long life, but only modest levels of efficiency and color rendering index (CRI).

Milliamp (mA): A measure of electrical current, the milliamp is one thousandth of an amp. Common LED drive currents include 350mA, 525mA and 700mA.

Multi-power Lamp: A lamp designed to produce multiple discrete light levels when inserted into a lamp socket controlled by a switching mechanism and is designated on the lamp packaging as being a multi-power lamp, e.g. 3-way lamp.

NADIR: the direction pointing directly below a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface there.

NEMA: National Electrical Manufacturers Association.

NRTL: Nationally Recognized Testing Laboratory as recognized by OSHA’s NRTL Program, which is a part of OSHA’s Directorate of Technical Support.

Omnidirectional: Occurring in many or all directions, such as traditional HID and other lamps. This quality of traditional lamps limits their efficiency due to the challenges inherent in directing the light produced onto desired surfaces.

Optical Efficiency: A measure of luminaire efficiency that focuses on the performance of optical components. Specifically, optical efficiency is the ratio of lighting delivered by a luminaire to the light produced by the lamps.

Phosphors: A substance that exhibits phosphorescence, which is the process of glowing occurring after exposure to energized particles. Many white LEDs are produced by combining GaN or InGaN LEDs, which produce blue light, with YAG (yttrium aluminum garnet) phosphors. See white phosphor LED.

Photopic Vision: Vision under well-lit conditions, mediated primarily by cone cells, which allows color perception. Photopic vision is the basis for most commonly-accepted lighting metrics, including those published by the IESNA.

P/N Junction: The border region in a semiconductor device formed by placing P-type (or materials carrying a positive charge) and N-type (or materials carrying a positive charge) semiconductor materials together in close proximity. It is the location in an LED where light is created, as well as the location inside the LED where heat is created.

Power over Ethernet (PoE): technology describes a system to pass electrical power safely, along with data, on Ethernet cabling.

Power Factor: A measure of the ratio of the real power flowing to a load divided by the apparent power. A load with low power factor draws more current than a load with a high-power factor.

Power Supply: A generic term for any device that supplies electrical or other types of energy to a load. In lighting, common power supplies include fluorescent and HID ballasts, various types of transformers, and LED drivers. The latter are available as devices providing either constant current or constant voltage.

Printed Circuit Board (PCB): A material used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets laminated onto a non-conductive substrate. Common types include FR-4 (Flame Retardant 4) and metal-core PCBs. The latter are commonly used with LEDs to aid in thermal management.

LED Lighting Terminology – Section R thru Z

Rated Lumen Maintenance Life (LP): The elapsed operating time over which the LED light source will maintain the percentage, p, of its initial light output, e.g., L70 (hours): time to 70% lumen maintenance (IES LM-80-08).

Rated Wattage: The wattage marked on the lamp.

Referenced Incandescent Lamp: A traditional incandescent lamp that predates the federal efficiency standards in the 2007 Energy Independence and Security Act.

Rods: Photoreceptor cells in the retina of the eye that can function in low light levels, and which are primarily responsible for night vision.

Run-up Time: The time between the application of power to the device and the time when the light output first reaches a specified percentage of stable light output, i.e., 80%, 90%, etc.

Scotopic Vision: Monochromatic vision in low light levels, which is produced by rod cells.

Secondary Optics: Materials modifying the distribution of light from, but not integral to a light source, including but not limited to lamp envelopes, reflectors, and total internal reflection optics.

Solid-State Lighting (SSL): Electronic components and systems based on the use of semiconductors rather than vacuum tubes. Common types of solid state components include integrated circuits, liquid-crystal displays, and LEDs.

Source Efficiency: A measure of luminaire efficiency that focuses on the performance of lamps. The source efficiency of LEDs is currently about equal with many fluorescent and HID sources, but the directional nature of light produced from LEDs delivers substantially higher fixture (or system) efficiency than traditional sources.

Standardized Color Ellipse: A MacAdam color ellipse defined by center chromaticity coordinates (CIE x, y) and a measure of certainty for detecting a color difference specified in standard deviation units called steps.

Thermal Efficiency: A measure of luminaire efficiency that focuses on the ability of the luminaire system to transfer heat from sensitive components, such as LEDs, to the outside environment. High levels of thermal efficiency are made possibly by using high-quality components (such as LEDs with low thermal resistance) and materials (such as aluminum alloys with low thermal resistance), as well as intelligent product designs.

TM-15-07: Rating system developed by IESNA which replaces the older IES cutoff classification system for controlling light emitted in unwanted regions surrounding a luminaire.

Traditional Lamps: Light sources developed and used during the last century including incandescent, fluorescent, HID and other sources.

UL: Underwriters Laboratories

Uplight: Light emitted from the luminaire directly into the sky which causes artificial sky glow and generally represents wasted energy. Uplight is a component of the new TM-15-07based BUG rating system, which replaces the older cutoff classification system.

Useful Life: The length of time an asset or device can be used without major refurbishing. In lighting, the useful life of lamps is typically stated at 70% of initial lumens since it is difficult to perceive this reduction in light output.

Voltage: Electrical potential difference, which is commonly expressed as (VA − VB). Voltage is conceptualized as the electrical driving force that drives a conventional electric current in the direction A to B. LED voltage is determined by the physical structure of the semiconductor material, and the level of light produced by the LED is determined largely by the level of current flowing to the LEDs.

Watts: A measure of power, or the rate of energy conversion. The watts consumed by an LED are typically derived from a relatively fixed voltage level and varying levels of current.

White Phosphor LEDs: Combinations of InGaN (indium gallium nitride) semiconductor material—which produces blue light—and YAG (yttrium aluminum garnet) phosphors create white light. Other LED systems deliver white light by combining red, green and blue (RGB) LEDs.