-------------------------------------

Ambient Temperature
The surrounding temperature within an environment.

Amperes
("Amps.") A measure of electrical current. Power (Watts) = Voltage (Volts) x Current (Amps).

American National Standards Institute (ANSI)
A consensus-based organisation which coordinates voluntary standards for the physical, electrical and performance characteristics of lamps, ballasts, luminaires and other lighting and electrical equipment.

Anode
The "positive" terminal of a diode.

Application
Also called "lighting application," it refers to the particular use the lamp is being put to. (e.g. retail lighting application.) The term can also refer in a general way to "application engineering" which deals with specific parameters 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.

Ballast Factor (BF)
This is the percentage of a lamp's rated lumen output that can be expected when operated on a specific, commercially available ballast. For example, a ballast with a ballast factor of 0.93 will result in the lamp's emitting 93% of its rated lumen output. A ballast with a lower BF results in less light output and also generally consumes less power.

Beam Angle (Viewing Angle)
The angular dimension of the cone of light from a source encompassing the central part of the beam to the angle where the light intensity is 50% of maximum. The beam angle sometimes called "beam spread" is often part of the ordering code for the reflector lamps. It can also be referred to as the viewing angle when applied to LEDs.

Beam Lumens
The total lumens present within the portion of the beam contained in the given beam angle.

Beam Spread
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
An ideal material that absorbs all incident radiation and re-emits the maximum possible radiation for a given temperature. The sun is the closest example of a blackbody. Incandescent lamps also closely resemble a blackbody.

Bulb
A loose way of referring to a lamp. "Bulb" refers to the outer glass bulb containing the light source.

Brightness
Brightness is the visual perception of the amount of light emission based on the luminance of a source.

-------------------------------------

Canadian Standards Association (CSA)
An organisation that writes standards and tests lighting equipment for performance as well as electrical and fire safety. Canadian provincial laws generally require that all products sold for consumer use in Canada must have CSA or equivalent approval.

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 reflector lamps and for luminaires with a lamp operating in them.

Candlepower
An obsolete term for luminous intensity; current practice is to refer to this simply as candelas.

Candlepower (Mean Spherical)
Initial mean spherical candlepower at the design voltage. Mean spherical candlepower is the generally accepted method of rating the total light output of miniature lamps. To convert this rating to lumens, multiply it by 12.57 (4 pi).

Cathode
The "negative" terminal of a diode.

CE
CE marking is a declaration from a manufacturer that the product conforms to the requirements of the appropriate European Directive, allowing quicker access to the European market.

Chip
A very small area of semi-conducting material. Also known as a "die," it is the "active" light-emitting component of an LED.

Chromaticity
Measure to identify the colour of a source, typically expressed as (x,y) coordinates on the CIE 1931 Chromaticity Diagram.

Chromaticity Coordinates
A system for measuring the colour of the light emitted from a source--either a primary source like a lamp or a secondary source like an illuminated object. The x, y, and z chromaticity coordinates relate to the response of the human eye to the primary colours of light of red, green and blue. Usually only two numbers, x and y coordinates ranging from 0 to 1 specify the chromaticity.

Coefficient of Utilisation (CU)
In general lighting calculations, the fraction of initial source lumens that reach the work plane. CU is a function of luminaire efficiency, room surface reflectances and room shape.

Colour (Dominant Wavelength)
LEDs are designed to emit light at specific wavelengths or colours. The dominant wavelength is a quantitative measure of an LED colour as perceived by the human eye and is usually measured in nanometres. In order to specify an LED, you must specify the colour or dominant wavelength range required for your application. Some applications may have colour constraints in order to meet specific government specifications or regulatory guidelines.

Colour Bin
LEDs are sorted according to their wavelength or chromaticity coordinates into different groupings or "bins."

Colour Rendering Index (CRI)
An international system used to rate a source's ability to render object colours. The higher the CRI (based upon a 0-100 scale) the richer colours generally appear. CRI ratings of various sources may be compared, but a numerical comparison is only valid if the sources are close in colour temperature and luminous flux. CRI differences among sources are not usually significant (visible to the eye) unless the difference is more than 3-5 points.

Colour Rendering Indicator
Draws attention to the fact that this is a source with high colour rendering, which helps objects and persons illuminated to appear more true to life.

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. Some CFLs have integral ballasts and medium or candelabra screw bases for easy replacement of incandescent lamps.

Colour Temperature (Correlated Colour Temperature - CCT)
A number indicating the degree of "yellowness" or "blueness" of a white light source. Measured in Kelvins, CCT represents the temperature a blackbody must reach to mimic the colour of the source. Yellowish-white ("warm") sources, like incandescent lamps , have lower colour temperatures in the 2700K-3000K range; white and bluish-white ("cool") sources, such as cool white (4100K) and natural daylight (6000K), have higher colour temperatures. The higher the colour temperature the whiter, or bluer, the light will be.

Cool White
A term loosely used to denote a colour temperature of around 4100 K. The Cool White (CW) designation is used specifically for T12 and other fluorescent lamps using halophosphors and having a CRI of 62.

Cosine-Corrected
An illuminance meter that measures the light level correctly irrespective of the angle the light is coming from.

-------------------------------------

Daylight Lamp
A lamp resembling the colour of daylight, typically with a coluor temperature of 5500 K to 6500K.

Dichroic Reflector (or Filter)
A reflector (or filter) that reflects one region of the spectrum while allowing the other region(s) to pass through. A reflector lamp with a dichroic reflector will have a "cool beam" i.e. most of the heat has been removed from the beam by allowing it to pass through the reflector while the light has been reflected.

Dimmable
Whether or not the source luminous flux 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.

Dominant Wavelength
A quantitative measure of the colour of an LED as perceived by the human eye. It is usually measured in nanometres.

-------------------------------------

Efficacy (Luminous Efficiency)
In lighting terms, efficacy or luminous efficiency is a measurement of how effective a light source is in converting electrical input power to LUMENS of visible light, expressed in LUMENS-PER-WATT (LPW). In scientific terms, efficacy is a measurement of the conversion between optical power (Watts) and luminous flux (lumens), based on the eye sensitivity function.

Efficiency (Wallplug)
The efficiency of a light source is simply the fraction of electrical energy converted to light, i.e. watts of visible light produced for each watt of electrical power with no concern about the wavelength where the energy is being radiated. For example, a 100 watt incandescent lamp converts 7% of the electrical energy into light; discharge lamps convert 25% to 40% into light.

The efficiency of a luminaire or fixture is the percentage of the lamp lumens that actually comes out of the fixture.

Electromagnetic Inference (EMI)
High frequency electronic ballasts and other electronic devices can produce a small amount of radio waves which can interfere with radio and TV. International standards and requirements must be met for EMI levels before an electronic device is considered compliant.

Electromagnetic Spectrum
A continuum of electric and magnetic radiation that can be characterised by wavelength or frequency. Visible light encompasses a small part of the electromagnetic spectrum in the region from about 380 nanometres (violet) to 770 nanometres (red) by wavelength.

Energy Star
A program to promote energy efficient consumer products set up by the Environmental Protection Agency in the United States in 1992.

Energy Policy Act (EPACT)
Comprehensive energy legislation passed by the U. S. Congress in 1992. The lighting portion includes lamp labeling and minimum energy efficacy (lumens/watt) requirements for many commonly used incandescent and fluorescent lamp types. Federal Canadian legislation sets similar minimum energy efficacy requirements for incandescent reflector lamps and common linear fluorescent lamps.

Energy Policy Act (EPACT) Indicator
Means this lamp is Federally regulated for Energy Efficiency.

Eye Sensitivity
A curve depicting the sensitivity of the human eye as a function of wavelength. 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 of the eye. (See Photopic, Scotopic, Fovea, Foveal vision)

-------------------------------------

Flammability Rating
Plastic materials used in electronics design should be certified to a suitable flammability rating to ensure the safety and reliability of the product. Flammability ratings are awarded by UL in North America, and IEC in Europe.

Flicker
The periodic variation in light level caused by AC operation that can lead to strobe effects.

Fluorescence
A physical phenomenon whereby an atom of a material absorbs a photon of light and immediately emits a photon of longer wavelength. If there is a significant delay the phenomenon is called phosphorescence rather than fluorescence. It is interesting that "phosphors" used in lamps exhibit "fluorescence," not "phosphorescence."

Fluorescent Lamp
A high efficiency lamp utilising an electric discharge through low pressure mercury vapor to produce ultraviolet (UV) energy. The UV excites phosphor materials applied as a thin layer on the inside of a glass tube which makes up the structure of the lamp. The phosphors transform the UV to visible light.

Footcandle (fc)
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. One footcandle is equal to one lumen per square foot. See also Lux.

Forward Current
Current through a diode in the direction of its greatest conduction.

Forward Voltage (Vf)
The voltage across a diode for a given forward current.

Fovea, Foveal Vision
A small region of the retina corresponding to what an observer is looking straight at. This region is populated almost entirely with cones, while the peripheral region has increasing numbers of rods. Cones have a sensitivity peaking in the yellow-green corresponding to the eye response curve.

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 colour 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. The halogen participates in a tungsten transport cycle, returning tungsten to the filament and prolonging lamp life.

High Intensity Discharge (HID) Lamp
A general term for mercury, metal halide and high-pressure sodium lamps. HID lamps contain compact arc tubes which enclose various gases and metal salts operating at relatively high pressures and temperatures.

-------------------------------------

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.

Illuminance Meter
A device that measures the illuminance at a location calibrated either in footcandles or in lux. (Also known as a light meter)

Incandescent Lamp
A light source that generates light utilising a thin filament wire (usually of tungsten) heated to white heat by an electric current passing through it.

Infrared Radiation
Electromagnetic energy radiated in the wavelength range of about 770 to 1,000,000 nanometres. Energy in this range cannot be seen by the human eye, but can be sensed as heat by the skin.

Intensity Bin
LEDs are sorted according to their intensity values into different groupings or "bins."

International Electrotechnical Commission (IEC)
A private organisation that defines standards for all electrical, electronic and related technology, with a view to safety, performance, and energy efficiency.

Inverse Square Law
Formula stating that if you double the distance from the light source, the light level goes down by a factor of 4, if you triple the distance, it goes down by a factor of 9, and so on.

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 (lux or footcandles) on a surface illuminated by a source or sources.

-------------------------------------

-------------------------------------

Kelvin
A unit of temperature starting from absolute zero, parallel to the Celsius scale. 0C is 273K.

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

Kilowatt Hour (kWh)
The standard measure of electrical energy and the typical billing unit used by electrical utilities for electricity use. A 100-watt lamp operated for 10 hours consumes 1000 watt-hours (100 x 10) or one kilowatt-hour. If the utility charges €0.14/kWh, then the electricity cost for the 10 hours of operation would be 14 cents (1 x €0.14).

-------------------------------------

Lamp
The term used to refer to the complete light source package, including the inner parts as well as 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.

Lamp Types
Filament lamps: Incandescent, Halogen, Halogen-IR.
Discharge Lamps: Fluorescent, HID (High Intensity Discharge)
HID Lamps: Mercury, HPS (High Pressure Sodium), MH (Metal Halide) and CMH (Ceramic Metal Halide)

Leadframe
A metallic frame used for mounting and connecting LED chips. The leadframe functions as the electrical leads of the device.

Lens
An optical element which controls the distribution of light by redirecting individual rays. Luminaires often have lenses in addition to reflectors.

Lifetime
LED reliability is described in terms of lifetime, which is the variation of light output with time, or lumen maintenance, for an LED operating in well controlled ambient conditions at a set current. LED Lifetime is critically dependent on LED junction temperature, forward current, and environmental conditions. For most lighting applications, lumen maintenance of 70% is necessary over the required operating period. Lumen maintenance of 50% is acceptable for decorative lighting applications.

Light
Radiant energy that can be sensed or seen by the human eye. Visible light is measured in lumens.

Light Emitting Diode (LED)
A semiconductor that directly converts electrical impulses into light. Some LEDs today incorporate fluorescent materials to change the colour characteristics of the emitted light.

Lumens
A measure of the luminous flux or quantity of light emitted by a source. For example, a dinner candle provides about 12 lumens. A 60-watt Soft White incandescent lamp provides about 840 lumens.

Lumen Maintenance
A measure of how well a lamp maintains its light output over time. It may be expressed numerically or as a graph of light output vs. time.

Luminaire
A complete lighting unit consisting of a lamp (or lamps), ballast (or ballasts) as required together with the parts designed to distribute the light, position and protect the lamps and connect them to the power supply. A luminaire is often referred to as a fixture.

Luminaire Efficiency
The ratio of total lumens emitted by a luminaire to those emitted by the lamp or lamps used in that luminaire.

Luminance
A measure of "surface brightness" when an observer is looking in the direction of the surface. It is measured in candelas per square meter (or per square foot) and was formerly referred to as "photometric brightness."

Luminous Efficacy
(See EFFICACY)

Luminous Intensity
A measure of the visibility of a light source generally expressed in candelas. It is defined as luminous flux per unit solid angle (steradian) in a given direction.

Lux (lx)
A unit of illuminance or light falling onto a surface. One lux is equal to one lumen per square meter. Ten lux approximately equals one footcandle.

-------------------------------------

Mean Lumens
The average light output of a lamp over its rated life. Based on the shape of the lumen depreciation curve, for fluorescent and metal halide lamps, mean lumens are measured at 40% of rated lamp life. For mercury, high-pressure sodium and incandescent lamps, mean lumen ratings refer to lumens at 50% of rated lamp life (See Lumen Maintenance).

Metal Halide Lamp
A high intensity discharge light source in which the light is produced by the radiation from mercury, plus halides of metals such as sodium, scandium, indium and dysprosium. Some lamp types may also utilise phosphor coatings.

Mesopic
Typically referring to nighttime outdoor lighting conditions, the region between PHOTOPIC and SCOTOPIC vision.

Monochromatic Light
Light with only one wavelength (i.e. colour) present.

-------------------------------------

Nanometre
A unit of wavelength equal to 1 x 10-9 m.

-------------------------------------

Operating Voltage
For electrical discharge lamps, this is the voltage measured across the discharge when the lamp is operating. It is governed by the contents of the chamber and is somewhat independent of the ballast and other external factors.

-------------------------------------

Package
LED's are available in either leaded-through-hole, or surface-mount packages. Through-hole LED's are ideal for wave solder circuit board applications. Most through-hole LED's are 2-leaded devices. Common through-hole package sizes include 3mm (T-1) and 5mm (T-1 *) diameter parts. Whereas, surface-mount packages are best used with reflow assembly. SMD devices are also useful when package size constraints are an issue.

Peak Wavelength
The wavelength at which peak optical power is emitted for an LED.

Phosphor
An inorganic chemical compound processed into a powder and deposited on the inner glass surface of fluorescent tubes and some mercury and metal-halide lamp bulbs. Phosphors are designed to absorb short wavelength ultraviolet radiation and to transform and emit it as visible light. In LEDs, a yellow phosphor is typically used in conjunction with a blue chip to produce white light.

Photometry
The measurement of light and related quantities.

Photopic
Vision for which the cones in the eye are responsible; typically at high brightness and in the foveal or central region.

Power Factor (PF)
A measure of the phase difference between voltage and current drawn by an electrical device, such as a ballast or motor. Power factors can range from 0 to 1.0, with 1.0 being ideal. Power factor is sometimes expressed as a percent. Incandescent lamps have power factors close to 1.0 because they are simple "resistive" loads. The power factor of a fluorescent and HID lamp system is determined by the ballast used. "High" power factor usually means a rating of 0.9 or greater. Power companies may penalise users for using low power factor devices.

-------------------------------------

Quartz
A name for fused silica or melted sand from which many high-temperature containers are fashioned in the lighting industry. Quartz looks like glass but can withstand the high temperatures needed to contain high intensity arc discharges.

-------------------------------------

Radiation
A general term for the release of energy in a "wave" or "ray" form. All light is radiant energy or radiation, as is heat, UV, microwaves, radio waves, etc.

Rated Lamp Life
For most lamp types (LEDs not included), rated lamp life is the length of time of a statistically large sample between first use and the point when 50% of the lamps have died. It is possible to define "useful life" of a lamp based on practical considerations involving lumen depreciation and colour shift.

Reflectance
The ratio of light reflected from a surface to that incident upon it.

Reflector Lamp (R)
A light source with a built-in reflecting surface. Sometimes, the term is used to refer specifically to blown bulbs like the R and ER lamps; at other times, it includes all reflector lamps like PAR and MR.

Reverse Voltage (VR)
Voltage across the diode for a given reverse current.

-------------------------------------

Scotopic
Vision where the rods of the retina are exclusively responsible for seeing, typically like the light levels in the countryside on a moonless, starlit night.

Scotopic/Photopic (S/P) Ratio
This measurement accounts for the fact that of the two light sensors in the retina, rods are more sensitive to blue light (scotopic vision) and cones to yellow light (photopic vision). The scotopic/photopic (S/P) ratio is an attempt to capture the relative strengths of these two responses. S/P is calculated as the ratio of scotopic lumens to photopic lumens for a light source on an ANSI reference ballast. Cooler sources (higher colour temperatures lamps) tend to have higher values of the S/P ratio compared to warm sources.

Spectral Power Distribution (SPD)
A graph of the radiant power emitted by a light source as a function of wavelength. SPDs provide a visual profile or "finger print" of the colour characteristics of the source throughout the visible part of the spectrum.

Specular Reflection
Reflection from a smooth, shiny surface, as opposed to diffuse reflection.

Spot
A colloquial term referring to a reflector lamp with a tight beam of light, typically around 10 degrees or less. It comes from the fact that such a lamp produces a narrow spot of light as opposed to a wide flood of light.

-------------------------------------

Task Lighting
Supplemental lighting provided to assist in performing a localised task, e.g. a table lamp for reading or an inspection lamp for fabric inspection.

-------------------------------------

Underwriters Laboratories (UL)
A private organisation which tests and lists electrical (and other) equipment for electrical and fire safety according to recognised UL and other standards. A UL listing is not an indication of overall performance. Lamps are not UL listed except for compact fluorescent lamp assemblies - those with screw bases and built-in ballasts.

Ultraviolet (UV) Radiation
Radiant energy in the range of about 100-380 nanometres (nm). For practical applications, the UV band is broken down further as follows:

• Ozone-producing - 180-220 nm
• Bactericidal (germicidal) - 220-300
• Erythemal (skin reddening) - 280-320
• "Black" light - 320-400

The International Commission on Illumination (CIE) defines the UV band as UV-A (315-400 nm); UV-B (280-315 nm) and UV-C (100-280 mm).  

-------------------------------------

Viewing Angle
The off-axis angle where the display may be satisfactorily viewed (defined by lenses, obstructions, or intensity decrease).

The viewing angle referred to as the 2-half theta angle (2Q * ) indicates how focused the light is when emitted from the LED. This angle is determined by measuring the angle from direct on-axis to the angle where intensity falls to * of the on-axis intensity, and then multiplying this difference by 2.

The shape of the encapsulant dome lens controls the viewing angle of the LED. Flat LEDs without domes generally have a very wide viewing angle. The choice of viewing angle also affects the LED intensity. As the viewing angle is increased, more area is covered by light, however the on-axis intensity is reduced.

For applications where the LED will project light onto a small area, or on an object far from the emitter, a narrow viewing angle is ideal. For applications where the LED will project light onto a large area, or on an object very close to the emitter, a wide viewing angle is ideal. For instance, backlighting an indicator or switch in a cavity of less than 18mm would typically call for a surface mount LED with a 120° viewing angle. Illuminating an object of 100mm x 100mm size that is 600mm away would require a 5mm LED with a 20° or smaller viewing angle.

Oval-viewing angle LEDs are available for applications requiring illumination of areas that are not square or circular. These LEDs have a wider viewing angle in either the horizontal or vertical direction.

Volt
A measure of "electrical pressure" between two points. The higher the voltage, the more current will be pushed through a resistor connected across the points. The volt specification of an incandescent lamp is the electrical "pressure" required to drive it at its designed point. The "voltage" of a ballast, (e.g. 277 V) refers to the line voltage it must be connected to.

Voltage
A measurement of the electromotive force in an electrical circuit or device expressed in volts. Voltage can be thought of as being analogous to the pressure in a waterline.

-------------------------------------

Warm White
Refers to a colour temperature around 3000K, providing a yellowish-white light.

Watt
A unit of electrical power. Lamps are rated in watts to indicate the rate at which they consume energy.

Wavelength
The distance between two neighbouring crests of a travelling wave. The wavelength of visible light is between 400 and 700 nanometres.

-------------------------------------

-------------------------------------

-------------------------------------

-------------------------------------