ABC of LED Lighting

Terms & Definitions used in the Lighting Industry
A

AC –  See alternating current

Additive Colour Model – A type of RGB colour model that describes how different proportions of red, green, and blue light combine to create colours. In the additive colour model, combining red, green, and blue light produces white light.

AlGaAs – One of the material systems for manufacturing LEDs that produce light in the red and amber portions of the visible light spectrum.

AllnGaP – the preferred LED (Light Emitting Diode) chip technology containing Aluminium, Indium, Gallium, and Phosphorous to produce red, orange and amber-colours.

Alternating Current – The flow of electricity (electric current) in a circuit that frequently alternates direction every second. AC (as opposed to direct current) is generally the method for delivering electric power to homes and buildings.

Ambient Temperature (Ta) – The air temperature surrounding the device usually stated as 25⁰C.

American National Standards Institute (ANSI) – A non-profit organization that develops voluntary consensus standards and conformity assessment systems for products, services, processes, systems, and personnel in the United States.

Ampere (Amp) – The unit for measuring rate of flow of electrical current: Current (Amps) = Power (Watts) / Voltage (Volts)

ANSI Binning – The system defined by the American National Standards Institute for the binning specifications for light emitting diodes.

Array – See LED Array

B

Bin (Binning) – The systematic dividing of distribution of performance parameters (Flux, Wavelength or CCT, and Vf) in to small finite groupings that may be selected to optimize assembly performance.

Beam Angle – The beam angle is the degree of width of the light that emanates from a light source. Specifically: The angle between those points on opposite sides of the beam axis where the intensity drops to 50% of maximum.

Black Body/Black Body Radiator – An object that absorbs all electromagnetic radiation falling on it. Because it reflects no light, a black body appears black. As a black body is heated to incandescence, it radiates light in a sequence of colours, from red to orange to yellow to white to blue, depending on its temperature. This colour sequence describes a curve within a colour space, known as the black-body curve.

Black Body Curve – A curve within a colour space describing the sequence of colours emitted by a black-body radiator at different temperatures.

Brightness – Often used incorrectly with respect to illumination as a synonym for luminous flux, an objective measurement of the visible power of a light source. The term is correctly used when describing screen brightness in a display or television. (see Nits).

C

Case Temperature – The temperature measured at the LED package or case.

CCT – See Correlated Colour Temperature.

Chip – See LED chip.

Chromaticity – An objective specification of the quality of a colour, independent of its luminance, and as determined by its own saturation and hue.

CIE – See International Commission on Illumination.

CIE 1931 Colour Space – A colour space created by the International Commission on Illumination (CIE) in 1931 to define the entire gamut of colours visible to the average viewer.

CIE Chromaticity Diagram – A horseshoe shaped line connecting the chromaticities of the spectrum of colours. (See Colour Definition, Chroma).

Colour Definition – The colour of uniformly illuminated objects described using three terms:

Hue: the situation when the appearance of different colours is similar (e.g. matching blues and pinks).

Lightness: a range of greyness between black and white.

Chroma: the degree of departure from grey of the same lightness and increasing colour (e.g. red, redder, pure red).

Colour Gamut – The range of colours within the CIE Chromaticity Diagram included when combining different sources.

Colour Model – An abstract mathematical model describing the way colours can be represented as groups of values or colour components. RGB (Red-Green-Blue) is a colour model with three colour components, and CMYK (Cyan-Magenta-Yellow and Key (Black)) is a colour model with four colour components.

Colour Rendering – A general expression for the effect of a light source on the colour appearance of objects.

Colour Rendering Index (CRI) – A measure of the degree of colour shift objects undergo when illuminated by the light source as compared with those same objects when illuminated by a reference source of comparable colour temperature. The reference source has a CRI of 100.

Colour Spectrum / Visible Spectrum – The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye, typically between 390nm and 750nm.

Colour temperature – The description used to describe the effect of heating an object until it glows incandescently, the emitted radiation, and apparent colour, changes proportional to the temperature; easily envisioned when considering hot metal in a forge that glows red, then orange, and then white as the temperature increases.

Conformal Phosphor Coating – Phosphor application process that uniformly coats the LED chip with phosphor.

Controller – A device that controls the output of colour-changing and tunable white lighting fixtures. Controllers typically have software components for configuring fixtures and designing and editing light shows, and hardware components for sending control data to fixtures.

Cool White – A description of a range of correlated colour temperatures from 5500K to 6500K.

Correlated Colour Temperature (CCT) – The absolute temperature of a blackbody whose chromaticity most nearly resembles that of the light source. Usually specified in Kelvin (K). The lower the Kelvin temperature, the warmer the light feels, or appears.

Current – The rate of flow of electric charge in a conductor, which is measured in amperes or amps.

CRI – See Colour Rendering Index.

D

DALI – See Digital Addressable Lighting Interface

Delivered Light – The amount of light a lighting fixture or lighting installation delivers to a target area or task surface, measured in footcandles (fc) or lux (lx).

Die – Chip: light emitting semiconductor.

Diffuser – An object with irregularities on a surface causing scattered reflections.

Digital Addressable Lighting Interface (DALI) – A digital communications protocol for controlling and dimming lighting fixtures, originally developed in Europe.

Direct-View Lighting Fixtures – Lighting fixtures intended for viewing, rather than for illumination. For example, arrays of direct-view fixtures or nodes are used in large-scale video displays, traffic signals, and signage applications.

Directional Light Source – A light source that emits light only in the direction it is pointed or oriented.

DMX – A digital communications protocol for controlling lighting fixtures, originally developed to control stage lighting.

Downlight – Either a simple light fitting recessed into a ceiling or bulkhead or alternatively an integrated light fitting complete with integral LED light engine and driver recessed into a ceiling or bulkhead usually.

Driver – Electronics used to power illumination sources. A driver regulates the current in order to maintain steady lumen output and prevent variation.

E

Efficacy – The light output of a light source divided by the total electrical power input to that source, expressed in lumens per watt (lm/W).

Efficiency – See Luminous efficiency.

ELV-type Dimmer – An electronic low voltage dimmer, used to dim LED lighting fixtures with electronic transformers.

Emergency Tubes – An LED tube which is able to function in emergency mode operating normally in typical daily use but adjusting to 50% of the normal light output when power outage occurs and which will continue to function for some time to permit occupants to exit the area or escape in an emergency.  It is a devise which operates on patented technology without the use of batteries thereby completely eliminating the need to maintain charging and discharging of conventional emergency lighting equipment.

Epoxy – Organic polymer frequently used for a dome or lens, often prone to optical decay over time, resulting in poor lumen maintenance. High quality LEDs such as Alt Products contain no epoxy in the optical system and deliver superior lumen maintenance.

Eye-sensitivity Curve – See spectral luminous efficiency function.

F

Flux / Luminous Flux – Luminous flux is the measure of the perceived power of light, adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light

Floodlight – A LED light housed within a metal body producing an intensely bright usually with a wide beam thereby flooding an area.

Forward voltage – The voltage across a semiconductor diode that is carrying current in the forward direction; it is usually approximately constant over the range of currents commonly used.

FR4 – A widely accepted printed circuit board (PCB) material which is fiberglass reinforced epoxy laminates that are flame retardant.

Freedom From Binning – Describes the case where the entire production of white LEDs can be described by a single CCT and within a declared number of MacAdam ellipses. No subdivision or colour binning of the LEDs is required for use in the intended application.

G

Ghosting – An effect that occurs when lighting fixtures in the OFF state faintly glow as a result of residual voltage in the circuit.

Glare – Direct glare is caused by light entering directly into the eye from a light source. Indirect glare is light reflected from a surface in the direction of the eye. Both can cause harm and cause visual discomfort or disability.

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

Growlights – An artificial light source designed to stimulate plant growth by emitting an electromagnetic spectrum appropriate for photosynthesis.  They are used where there is either no naturally occurring light or where supplemental light is required.

H

Heat Sink – A part of the thermal system that conducts or convects heat away from sensitive components, such as LEDs and electronics.

High Power LED – A high power LED, sometimes referred to as a power LED, is one that is driven at a current of 350 mA or higher.

High-brightness – High-brightness is a term that is often applied to an LED but has no measured meaning and does not indicate any level of performance.

Hot/Cold Factor – The relative light output performance at a temperature compared to the light output at a nominal or test temperature. For Alt products this is the relative light output at 65C Tj compared to 25C Tj.

Hot Testing – LED performance testing and specification at an elevated temperature of 85°C.

I

IES / IESNA/IESSA – See Illuminating Engineering Society.

Illuminance – The intensity of light falling on a surface area. If the area is measured in square feet, the unit of illuminance is footcandles (fc). If measured in square meters, the unit of illuminance is lux (lx).

Illuminating Engineering Society of North America (IESNA) – The recognized technical authority on illumination, communicating information on all aspects of good lighting practice to its members, to the lighting community, and to consumers through a variety of programs, publications, and services.

Illuminating Engineering Society of South Africa – The recognised technical authority on illumination, communicating in formation on all aspects of good lighting to its members, to the lighting community, and to consumers through a variety of programs, publications and services.

Inboard Power Integration – An approach to power management that integrates the power supply directly into a fixture’s circuitry, creating an efficient power stage that consolidates line voltage conversion and LED current regulation.

Infrared (Near) – Electromagnetic radiation with wavelength range from 700 nm – 3000 nm.

InGaN LED – The preferred LED (Light Emitting Diode) semiconductor material system containing Indium, Gallium, and Nitrogen to produce green, blue and white-coloured LED light sources.

Integrating Sphere – A device used for a variety of optical, photometric, or radiometric measurements.

J

Junction Temperature – Junction temperature, noted as Tj, is the temperature of the LED’s active region.

K

Kelvin Temperature – Term and symbol (K) used to indicate the comparative colour appearance of a light source when compared to a theoretical blackbody. Yellowish incandescent lamps are 3000K. Fluorescent light sources range from 3000K to 7500K and higher.

Kilowatt (kW) – A measure of electrical power equal to 1000 watts.

Kilowatt Hour (kWh) – A standard measurement of electrical energy equal to one kilowatt of electricity used over a period of one hour.

L

Leading Edge Dimmer – A type of dimmer that regulates power to lamps by delaying the leading edge of each half-cycle of AC power. Compatible with many LED fixtures.

LED – See Light Emitting Diode.

LED Array – An assembly of LED packages 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 an LED driver.

LED Chip (Chip) – The light producing semiconductor device that may or may not be incorporated into an LED.

LED Driver – An electronic circuit that converts input power into a current source — a source in which current remains constant despite fluctuations in voltage. An LED driver protects LEDs from normal voltage fluctuations, over-voltages, and voltage spikes.

LED Light Engine – An integrated assembly comprised of LEDs or LED arrays, LED driver, and other optical, thermal, mechanical, and electrical components.

LED Luminaire – A complete lighting unit consisting of LED-based light emitting elements and a matched driver together with parts to distribute light, to position and protect the light emitting elements, and to connect the unit to a branch circuit. The LED based light emitting elements may take the form of LED packages, (components), LED arrays (modules) LED Light Engine, or LED lamps. The LED luminaire is intended to connect directly to a branch circuit.

LED Module – See LED array.

Light Emitting Diode (LED) – A Light Emitting Diode (LED) is a solid-state semiconductor device that converts electrical energy directly into light. On its most basic level, the semiconductor is comprised of two regions. The p-region contains positive electrical charges while the n-region contains negative electrical charges. When voltage is applied and current begins to flow, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths.

Light Output – See Luminous Flux.

Lumen (lm) – The international (SI) unit of luminous flux or quantity of light and equals the amount of light that is spread over a square foot of surface by one candle power when all parts of the surface are exactly one foot from the light source. For example, a dinner candle provides about 12 lumens

Lumen Depreciation – Describes the percentage of light lost relative to the initial lumen output. See lumen maintenance for more information.

Lumen Maintenance – The luminous flux at a give time in the life of the LED. This is expressed as a percentage of the initial luminous flux.

Lumen Maintenance Curve – A graph illustrating the predicted average light output behaviour over time of a single LED or solution.

Lumen Output – The total lumens emitted of a light source, system, or solution.

Luminaire – A lighting fixture complete with installed lamps and other accessories.

Luminous Efficiency – The percentage of total lamp lumens that a lighting fixture, luminaire, or system emits, minus any blocked or wasted light.

Luminous Flux – See Flux.

Lux (lx) – The SI (International) unit of illuminance, or luminous flux incident on a unit area, frequently defined as one lumen per square meter (lm/m2).

M

MacAdam Ellipse – A MacAdam ellipse is the region on a chromaticity diagram which contains all colours which are indistinguishable, to the average human eye, from the colour at the centre of the ellipse.

Material System – The material, such as aluminium indium gallium phosphide (AlInGaP) and indium gallium nitride (InGaN), used within an LED to produce light of a specific colour.

MCPCB – A widely accepted Printed Circuit Board (PCB) material with a Metal Core (MC) for better thermal performance.

Mesopic Vision – It is a combination of Photopic and Scotopic vision in low but not quite dark lighting situations.  Mesopic light levels range from luminances of approximately 0.001 lux to 3 lux.  Most night time outdoor and traffic lighting scenarios are in the Mesopic range.  It is considered to apply more and more in indoor environments such as shopping malls and retail shops.

N

Nanometer – A unit of linear measurement equal to 1 billionth of a meter (1,000,000,000 meter)

Nits – Measurement of display screen brightness. 1 nit = 1 cd/m2.

Neutral White (Daylight) – A description of a range of correlated colour temperatures from 4000K to 4500K.

NTSC Colour Space – The range of colours within the CIE Chromaticity Diagram included when combining phosphor based RGB sources in CRTs such a televisions and computer monitors.

O

Onboard Power Integration – An approach to power management that integrates the power supply into a fixture’s housing, eliminating the need for an external power supply.

Operating Temperature – It is the temperature at which an electrical device operates.  The device will operate effectively within a specified temperature range.  Outside of this range the device may fail.

Organic Light-emitting Diodes (OLED) – Organic light-emitting diodes (OLEDs) are based on organic (carbon based) materials. In contrast to LEDs, which are small point sources, OLEDs are made in sheets which provide a diffuse area light source. OLED technology is developing rapidly and is increasingly used in display applications such as cell phones and PDA screens. However, OLEDs are still some years away from becoming a practical general illumination source. Additional advancements are needed in light output, colour, efficiency, cost, and lifetime.

P

Performance – Meeting the required criteria for a given task or application against preset or known standards which can include cost.

P-N Junction – Area on an LED chip where the positively and negatively charged regions meet. When current is applied, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths. In short, the area on a chip where light is produced.

P-type Material – In a diode’s p-n semiconductor junction, p-type material is positively charged. Atoms in the p-type material have electron holes — electrons missing from their outer rings.

PC Amber (Phosphor Converted) – PC amber is a method of making amber coloured LEDs from royal blue LED chips. It requires the use of special phosphors and results in a more reliable, less temperature sensitive, and more consistent amber LED.

Phosphor – A coating of phosphorescent material which photons from a royal blue LED pass through causing those photons to exit with a different colour property.

Phosphor Conversion – This is the process by which photons from an LED chip are converted to a different colour. White LEDs and some coloured LEDs are made using phosphor conversion.

Photopic Vision – It is the vision of the eye under well –lit conditions including daylight.  Photopic vision allows colour perception mediated by the cone cells and a significantly higher visual acuity and temporal resolution than is possible with Scotopic vision.

Planckian Black Body Locus – The line on the CIE Chromaticity Diagram that describes the colour temperature of an object when heated from approximately 1,000K to more than 10,000K.

Power Factor – The active power divided by the apparent power (i.e., product of the rms input voltage and rms input current of a driver).

Power Factor Correction – In an electronic device, such as an LED lighting fixture, a system of inductors, capacitors, or voltage converters to adjust the power factor of electronic devices toward the ideal power factor of 1.0.

Pulse Width Modulation (PWM) – A method, used by LED drivers, to regulate the amount of energy to the LEDs. PWM turns LEDs on and off at high frequency, reducing total ON time to achieve a desired dimming level.

Q

Quality – The standard of something as measured against other products of a similar kind.

R

Radiant Flux – The total energy emitted by a light source across all wavelengths, measured in watts.

Radiometry – The measurement of radiant energy (including light) in terms of absolute power. Compare photometry.

Reflectance – The ratio of light reflected by a surface to the amount of light originally striking that surface

Reflectance = reflected light/incident light.

Refraction – The bending of light due to a change in its speed due to light passing from one transparent medium into another transparent medium.

Remote Phosphor – A phosphor conversion technique in which photons from a royal blue LED pass through a phosphor material that is not attached to the LED chip.

Resistance – The electrical resistance of an electrical element is the opposition to the passage of an electric current through the element or device; the inverse quantity is electrical conductance, the ease at which an electric current passes.

RGB Colour Model – An additive colour model in which red, green, and blue light are added together in different proportions to produce a broad range of colours, including white.

RGB White – A method of producing white light by combining the output from red, green, and blue LEDs.

S

Scotopic Vision – It is the vision of the eye under low light conditions.  In the human eye the cone cells are non-functional in low light.  Scotopic vision is produced exclusively through rod cells which are most sensitive to wavelengths of around 498nm (green-blue) and are insensitive to wavelengths longer than about 640nm (red).  Scotopic vision occurs at luminance levels of  10-² lux to 10-6.

SDCM – See standard deviation of colour matching.

SMDs – Surface-mount LEDs.

Solder Point Temperature (Ts) – Solder point temperature as specified by ENERGY STAR®.

Solid-state lighting – A description of the devices that do not contain moving parts or parts that can break, rupture, shatter, leak or contaminate the environment.

S/P Ratio (Scotopic/Photopic Ratio) – a multiplier that measures how much emitted light is useful to the human eye. These useful lumens are known as visually effective lumens (VELs).

Spectral Luminous Efficiency Function – A bell-shaped curve describing the sensitivity of a human eye with normal vision to the spectrum of visible light. Also known as the eye-sensitivity curve.

Spotlight – A powerful light focused so as to illuminate a small area, usually mounted so that it can be aimed at will for a particular purpose.

sRGB – A Standard Default Colour Space for the Internet created by Hewlett-Packard and Microsoft to support a standard colour space within the Microsoft operating systems, HP products, and others.

Standard deviation of colour matching (SDCM) – Describes the difference between two colours. A difference of one to three SDCM “steps” is virtually imperceptible, a difference of four SDCM steps is just noticeable, and a difference of more than four SDCM steps is readily visible.

Steradian – The standard unit of solid angle. Describes two-dimensional angular spans in three-dimensional space.

Subtractive Colour Model – A colour model that applies to reflective surfaces such as paints, dyes, and inks. Combining red, green, and blue in equal amounts produces black.

T

Ta – See Ambient Temperature

Tc – See Case Temperature

Thermal management – Controlling the operating temperature of the product through design, examples includes heat sinks and improved airflow.

Thermal Pad Temperature – The measured temperature of the thermal pad during testing. The thermal pad aides in the conduction of heat away from the component being cooled and into the heatsink. For more information refer to LUXEON® Rebel and LUXEON® Rebel ES Assembly and Handling Guide application brief 32.

Thermal Resistance (K/W) – The property of a material’s ability to conduct heat.

Tj – See Junction Temperature

Tp – See Thermal Pad Temperature

Trailing Edge Dimmer – A type of dimmer that regulates power to lamps by delaying the end of each half-cycle of AC power. Compatible with many LED fixtures.

Ts – See Solder Point Temperature.

Tunable White Light – White-light LED fixtures that combine channels of warm white and cool white LEDs to produce a range of colour temperatures.

U

Ultraviolet (UV) – Electromagnetic radiation with wavelength shorter than that of visible light.

Useful Life – The amount of light a lighting fixture delivers in an application, minus any wasted light.

V

Visual Comfort Probability (VCP) – The VCP for a lighting system is the percent of observers expected to find the glare acceptable in a specific location from a specific direction. The higher the VCP, the more comfortable observers find the space.

Volt – The term used to describe the electrical potential difference between oppositely charged conductors, for example there is a 1.5V potential between the top and bottom of an AAA battery.

W

Wall Plug Efficiency – This typically refers to the effectiveness of converting electrical power to light output. It is defined as the ratio of the radiant flux to the input electrical power.

Warm White – A description of light with a correlated colour temperature between 3000K and 3500K, usually perceived a slightly yellow.

Watt – The unit of electrical power as used by an electrical device during its operation. Many lamps come with rating in watts to indicate their power consumption.

White Point – The Coordinated Colour Temperature (CCT) defined by a line perpendicular to the Planckian Black Body Curve and intersecting the measured chromaticity.

PHILIP HAMMOND

BHA SCHOOL OF LIGHTING – 6 NOVEMBER 2017

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