Terminology

From ampere to volt, LPI presents a list of terms commonly used to discuss LED technology and lighting generally.

AlInGaP (aluminum indium gallium phosphide): An LED semiconductor material used to manufacture LEDs that emit red and green light.

Ampere: A measure of the flow of electrical current per unit time.  One ampere (A) corresponds to the passage of one coulomb’s worth of charge every second (1 A = 1 C/s).

Array: An order or arrangement of LEDs.

Chip: Usually made up of silicon, a chip is a small semiconductor which contains hundreds and thousands of electronic components. Chips area also called integrated circuits.

Colour gamut: The complete subset of colours that can be accurately represented in a given circumstance.

Colour rendering index (CRI): A measure of the degree of colour shift an object undergoes when illuminated by a light source as compared to a reference source of the same colour temperature. CRI is expressed on a scale of 0-100, with a higher value representing less colour distortion, or a more “accurate” colour. Natural daylight is rated 100.

Colour spectrum: The distribution of colours produced when light is dispersed by a prism.

Compact fluorescent lighting (CFL): A type of fluorescent lamp. Many CFLs are designed to replace incandescent lighting and can fit in existing light fixtures formerly used for incandescent bulbs. Compared to general service incandescent lamps giving the same amount of visible light, CFLs consume less power and last longer.

Compound semiconductor: A semiconductor that is composed of two or more elements.

Correlated Colour Temperature (CCT): A scale for measuring the temperature of an LED light source’s white light.  It uses the Kelvin (K), and one degree Kelvin equals one degree Celsius.  The scale is based on the principle that as an object is heated, the colour of light it emits changes.  A piece of metal, for example, will appear red, then white, and then blue as its temperature rises.   LED white lights are commonly divided into warm white (CCT = 2700-3000K) natural white (CCT = 4200-4500K), and true white (CCT = 5000-6000K).   Earlier LEDs were characterized for producing white light with a bluish tinge, giving the light a cold appearance.  These LEDs had CCTs in the 8000-10 000K range.  In contrast, current LED white lights have warmed considerably and can now replace conventional lights even in homes and restaurants, where warmer white light is especially desirable.

Coulomb: A unit of electric charge. One coulomb (C) equals the charge transported by one ampere in one second.

Delivered light: A concept that emphasizes the amount of light reaching a surface or area, as opposed to the amount of light a lamp produces.  Delivered light is therefore a more functional and practical measure of a light source’s ability to light a space.  LEDs are often criticized because they produce smaller quantities of light than the conventional lights they are to replace.  However, since LEDs emit their light far more directionally, virtually none of the light produced is wasted.  As a result, LED light sources provide light levels comparable to conventional light sources using far less light, and far less power.

Die: A semiconductor that has not yet been packaged. Also known as a chip.

Epitaxy: The process of depositing a thin layer of single crystal material over a single crystal substrate. In semiconductors, the deposited film is often the same material as the substrate.

Flux: The sum of all lumens emitted by a light source.

Incandescent lighting: Light produced when a filament is heated to incandescence using an electric current (e.g., light bulb). Incandescent lighting is very inefficient—turning much of its energy into heat rather than light—and is gradually being replaced in many applications by LEDs and other devices.

InGaN (indium gallium nitride): A semiconductor material composed of a mix of gallium nitride and indium nitride, which is used to manufacture blue- and green-coloured light-emitting diodes (LEDs).

Lamp: In conventional lighting, lamps are the actual light sources and typically comprise a filament or gas, a containing bulb, and base or pins for connecting to a fixture and current supply.  There are LED equivalents for most common conventional lamps.  Increasingly, LED lights combine lamps, fixtures, and other components into one product.

Luminaire: In conventional lighting, a luminaire comprises a lamp and the fixture, ballast, and other controls necessary to supply and regulate current to the lamp.  In LED luminaires, these components are often integrated, so that the lamp is indistinguishable from the fixture.

LED: Also known as a light-emitting diode, an LED is a solid-state semiconductor that emits light. LEDs are used in a variety of display and lighting applications, and consume less power than incandescent bulbs.

Light engine: A subsystem used to generate light, which typically includes a lamp module, optics and projection lens.

Light source: Any device serving as a source of illumination.

LM-79: A protocol described by the Illumination Engineering Society for testing overall LED lighting products.  LM-79 testing is separate and distinct from LM-80 testing, since the former deals with overall light delivery systems comprising light sources (LED chips and modules), drivers, heat sinks, and lenses, while the latter deals only with the testing of LED light sources.

LM-80: A protocol described by the Illumination Engineering Society for testing LED light sources (chipsets, modules) to determine how their light output varies over time.   To be LM-80 compliant, manufacturers must test their products for a minimum of 6000 hours, and testing to 10 0000 hours is recommended.

Lumen: A unit of measurement that expresses the total quantity of light given off by a source, regardless of direction. One lumen is equal to the amount of light that one candle emits over one square foot of surface that is exactly one foot away from the flame.

Lumen depreciation: A term describing the gradual loss of light output. All artificial light sources, conventional and LED alike, experience a decline in lumen output over their working lives.

Lumen maintenance: Measured in hours, lumen maintenance refers to the period during which an LED lighting product maintains its initial lumen output.

Luminous efficiency: A measure of light output relative to input power.  Measured in lumens per watt (lm/W).  Incandescent lamps have luminous efficiencies less than 20 lm/W.  Halogen lamps generally have luminous efficiency of approximately 22 to 23 lm/W.  LED lamps now boast luminous efficiencies of 100  lm/W and are steadily increasing.

lux: A unit of illumination intensity.  One lux equals one lumen per square meter (lm/m2).

L70: Commonly used to describe an LED lamp or luminaire’s useful life, L70 refers to the number of hours at which the product’s lumen output will have declined to 70 percent of its initial lumen output.  L70 is significant because most people will not notice a gradual loss in light output until it declines by 30 percent, which corresponds to the L70 level.

Nit: A unit of luminance used for estimating brightness.

Packaged LED: An LED package has an optical lens, bonding wire (to bond the package to the printed circuit board), electrodes, and resin to encapsulate the LED for protection.

RGB: An acronym for red, green and blue, which are the three primary colours of light. Also refers to the colour model for displays and monitors, where combinations of illuminated red, green and blue pixels are used to create a wide variety of colours.

Solid-state lighting (SSL): A form of lighting that makes use of light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), or polymer light-emitting diodes (PLEDs) as sources of illumination, as opposed to electrical filaments or gas.

Total cost of light: The sum of all expenses generated in the production of light.  In most cases, this value is the sum of the electricity costs to power a light, the cost of the lamps that generate the light, and any maintenance charges incurred when servicing the light, for example when changing lamps.  For most conventional lights, the total cost of light primarily reflects hydro costs.  For most LED lights, the total cost of light primarily reflects a light’s purchase price.  However, as LED lights consume so much less power over their lifespans, their total cost of light is often lower, as much as 75 percent lower, than a comparable conventional light source.  To read more about comparisons between specific conventional lamps and their LED replacements, visit our retrofit programs page.

Thermal management: The ability to control the temperature (heat) of the device junctions in packaged LEDs, often through the use of heat sinks. Junction heat can negatively impact the performance of LED lighting, including output, colour and lifetime.

Thermal resistance: The measure of a material’s resistance to heat flow. In packaged LEDs, thermal resistance is used as an indirect method of determining LED junction temperature.

Volt: A unit of measurement for electric potential and electromotive force.  One volt (V) corresponds to one joule (J) of energy per coulomb (C) of charge (1 V = 1 J/C).

Watt: A unit of measurement for power.  One watt (W) is equal to one joule of energy per second (1W = J/s).