Glossary

Alternating Current (AC)
Electrical current in which the flow of electric charge continually reverses direction.

Ambient Temperature
Temperature within an environment.

Ampere (Amp)
Measure of electrical current.

Anode
Positive terminal of a diode.

Ballast  
Device that limits the amount of current in an electric circuit.

Beam Angle       
Size of the cone of light produced by a light source expressed in degrees.

Candela (cd)
Measure of luminous intensity of a light source.

Cathode
Negative terminal of a diode.

CE marking
Certifies that a product has met EU consumer safety, health, or environmental requirements.

Centre Beam Candle Power (CBCP)        
Brightness measured at the centre of a light beam.

Chromaticity
Measure of colour quality.

Colour Rendering Index (CRI)
International system used to rate a lamp’s ability to render object colours. The higher the CRI (based on a 0 – 100 scale) the richer colours generally appear. Natural outdoor light has a CRI of 100.

Colour Spectrum
The distribution of colours produced when a prism disperses light.

Colour Temperature (CT)
Measure of the ‘yellowness’ or ‘blueness’ of a white light source expressed in kelvins. Yellowish-white (‘warm’) sources, like incandescent lamps, have lower colour temperatures in the 2700K – 3000K range; white and bluish-white (‘cool’) sources, such as natural daylight (6000K), have higher colour temperatures.

Compact Fluorescent Lighting (CFL)
Small-diameter, single-ended fluorescent lamps bent to form a compact shape. Commonly referred to as ‘Eco-Lights’ in New Zealand.

Cool White
A description of light with a Correlated Colour Temperature between 5500K and 7500K, usually perceived as slightly blue.

Correlated Colour Temperature (CCT)
Comparative colour appearance of a light source when compared to a theoretical ‘ideal black body’ expressed in kelvins (K).Yellowish incandescent lamps are around 3000K. Fluorescent light sources range from 3000K to 7500K and higher. Also known as Kelvin Temperature.

Dichroic Reflector
Reflector (or filter) that reflects one region of the colour spectrum while allowing the other regions to pass through. Commonly used in MR16 and GU10 halogen lamps.

Diffuser               
Optical element used to mix light rays to improve uniformity of light.

Direct Current (DC)
Electrical current in which the flow of electric charge moves in only one direction.

Directional Light
Light that travels in a specific direction without first being reflected off another surface. Most LED lighting products are directional because light projects directly from the light source itself.

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

Driver Efficiency
Measure of the efficiency of the driver components. The ratio of the power delivered from the driver divided by the power required to operate the driver.

Efficacy or Luminous Efficacy
Measurement of how effective the light source is in converting electrical energy to lumens of visible light, expressed in lumens per watt (LPW).

Efficiency
The fraction of electrical energy converted to light by a light source, i.e. watts of visible light produced for each watt of electrical power.

Fluorescent Light
Efficient light source consisting of a glass tube filled with low-pressure mercury vapour. Electrical discharge through the vapour produces ultraviolet light that excites phosphor materials on the inside of the tube, which then emit visible light.

Flux
Sum of lumens emitted by a light source.

Footcandle (fc)
Unit of illuminance or light falling onto a surface. One footcandle is the light level on a surface one foot from a standard candle.

Full Spectrum Lighting
Marketing term typically associated with light sources that are similar to some forms of natural daylight (5000K+ CT, 90+ CRI), but sometimes more broadly used for lamps that have a smooth and continuous colour spectrum.

Heat Dissipation
Transition of thermal energy from a hotter object to a cooler object. Achieved with LEDs primarily by mounting them on heat sinks made from high quality aluminium and other alloys.

High Intensity Discharge (HID)
Efficient electrical lamp filled with gases and other compounds in which an electric arc is passed between tungsten electrodes to produce light.

High Pressure Sodium (HPS)
A popular type of High Intensity Discharge (HID) lamp offering a relatively warm Correlated Colour Temperature (CCT), high levels of efficiency, long life, but only modest levels of Colour Rendering Index (CRI).

Illuminance
‘Density’ of light falling onto a surface measured in footcandles or lux.

Illuminance Meter
Device that measures illuminance in either footcandles or lux. Also known as a light meter, lux meter, or footcandle meter.

Incandescent Lighting
Light produced when a filament is heated to incandescence using an electric current such as in a light bulb. Incandescent lighting is very inefficient, with much of the energy wasted as heat rather than turned into light.

Induction Lighting
Long-life lamps in which gases are excited directly by microwaves (produced by a coil) that induce electromagnetic fields.

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

Ingress Protection (IP) Rating
Specifies the strength of enclosures that house electronic equipment.

Kelvin (K)
Unit of temperature starting from absolute zero, parallel to the Celsius or Centigrade scale.

Kelvin Temperature
See Correlated Colour Temperature.

Kilowatt (kw)
Measure of electrical power equal to 1000 watts.

Kilowatt Hour (kWh)
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 $0.15/kWh, then the electricity cost for the 10 hours of operation would be 15 cents (1 x $0.15).

Lamp
Term used to refer to the complete light source package, including the inner parts as well as the outer bulb or tube.

Light Emitting Diode (LED)
Solid-state semiconductor device that converts electrical energy directly into light.

LED Driver
See Driver.

LED Junction Temperature (TJ)
Temperature of the positive/negative electrical junction inside an LED lamp.

Lens
Transparent or semi-transparent element that controls the distribution of light by redirecting individual rays.

Light Engine
Subsystem used to generate light, which typically includes a lamp module, optics, and projection lens.

Lumen
Measure of the luminous flux or quantity of light emitted by a source. A dinner candle provides about 12 lumens. A 60-watt ‘Soft White’ incandescent lamp provides about 840 lumens.

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

Lumen Maintenance
Measure of how well a lamp maintains its light output over time, expressed numerically or as a graph of light output vs time.

Lumens per Watt (LPW)
Measure of lighting efficiency that indicates how much light is emitted per watt of electricity used.

Luminaire
Lighting fixture complete with lamp, housing, power supply, and optical components used to direct light.

Luminance
Measure of ‘surface brightness’ expressed in candelas per square meter (or per square foot).

Luminous Intensity
Measure of the visibility of a light source generally expressed in candelas.

Lux
Unit of illuminance or ‘density’ of light falling onto a surface. One lux is equal to one lumen per square meter. Ten lux equals approximately one footcandle.

Metal Halide (MH) Lamp
High intensity light source produced by the radiation from mercury, plus halides of metals such as sodium, scandium, indium and dysprosium.

Natural White
Light with a Correlated Colour Temperature between 4500K and 5500K, usually perceived as white.

Operating Life
How long a light will last at 100% brightness expressed as the average Mean Time Before Failure (MTBF).  Also known as lifespan.

Operating Voltage
The voltage that a circuit component needs in order to function properly.

Optical Efficiency
Measure of the efficiency of the optical components of a luminaire.

PAR Lamp
Acronym for Parabolic Aluminised Reflector, a precision pressed-glass reflector lamp.

Polarity
Some lamps must be installed in correctly oriented to match the polarity of the lamp pins to the polarity of the sockets they plug into. In most lamps, however, this is not an issue.

Power Factor
Measure of the ratio of the real power flowing to a load divided by the apparent power. Power factors can range from 0 to 1.0, with 1.0 being ideal.

Power Supply
Any device that supplies electrical or other types of energy. In lighting, common power supplies include fluorescent and HID ballasts, various types of transformers, and LED drivers.

RGB
Acronym for Red, Green, and Blue, 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.

RoHS Compliance
Restricts the use of certain dangerous substances commonly used in electrical and electronic equipment. A RoHS compliant component is tested for the presence of lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenyl ethers.

Solid State Lighting (SSL)
Lighting that uses semiconductor light-emitting diodes (LEDs), organic light-emitting diodes (OLED), or polymer light-emitting diodes (PLED) as sources of illumination rather than electrical filaments, plasma (used in arc lamps such as fluorescent lamps), or gases.

Thermal Efficiency
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.

Thermal Management
Ability to control the temperature (heat) of the electrical junctions in LEDs, often through the use of heat sinks.

Thermal Resistance
Measure of a material’s resistance to heat flow.

Transformer
An electrical device used to raise or lower the voltage of alternating current. For example, many lighting products require 12v current but mains power is supplied at 240v, so the voltage needs to be ‘transformed’ from 240v down to 12v. LED drivers perform a similar function.

Warm White
Light with a Correlated Colour Temperature between 3000K and 3500K, usually perceived as slightly yellow.

Watt
Unit of electrical power used by electrical devices. Many lamps come with a rating in watts to indicate their power consumption. A light source with a higher lumen per watt value is more efficient.