Glossary

AMPERE
The standard unit of measurement for electric current that is equal to one coulomb per second. It defines the quantity of electrons moving past a given point in a circuit during a specific period. Amp is an abbreviation. Current (Amps) = Power (Watts) / Voltage (Volts)

ARC TUBE
The tube in an HID lamp in which the primary light emitting discharge takes place. Made of clear quartz or ceramic, and may be enclosed by an outer glass envelope.

BAFFLE
A single opaque or translucent element used to control light distribution at certain angles.

BALLAST
A device used to operate fluorescent and HID lamps. The ballast provides the necessary starting voltage, while limiting and regulating the lamp current during operation.

BALLAST CYCLING
Undesirable condition under which the ballast turns lamps on and off (cycles) due to the overheating of the thermal switch inside the ballast. This may be due to incorrect lamps, improper voltage being supplied, high ambient temperature around the fixture, or the early stage of ballast failure.

BALLAST EFFICIENCY FACTOR
The ballast efficiency factor (BEF) is the ballast factor (see below) divided by the input power of the ballast. The higher the BEF (within the same lamp–ballast type) the more efficient the ballast.

BALLAST FACTOR
The ballast factor (BF) for a specific lamp–ballast combination represents the percentage of the rated lamp lumens that will be produced by the combination.

BEAM EFFICIENCY
The percentage difference between the beam lumens and the rated lamp lumens.

BEAM LUMENS
The accumulated total lumens within the “beam” of the luminaire; designated by the 50% maximum candela measurement.

CANDELA
Unit of luminous intensity, describing the intensity of a light source in a specific direction. As defined by the international metric standard (SI). The term, retained from the early days of lighting, defines a standard candle of a fixed size and composition as a basis for evaluating the intensity of other light sources.

CANDELA DISTRIBUTION
A curve, often on polar coordinates, illustrating the variation of luminous intensity of a lamp or luminaire in a plane through the light center.

CANDLEPOWER
A measure of luminous intensity of a light source in a specific direction, measured in candelas (see above).

COEFFICIENT OF UTILIZATION
The ratio of lumens from a luminaire received on the work plane to the lumens produced by the lamps alone. (Also called “CU”)

COLOUR RENDERING INDEX (CRI)
A scale of the effect of a light source on the colour appearance of an object compared to its colour appearance under a reference light source. Expressed on a scale of 1 to 100, where 100 indicates no colour shift. A low CRI rating suggests that the colours of objects will appear unnatural under that particular light source.

COLOUR TEMPERATURE
The colour temperature is a specification of the colour appearance of a light source, relating the colour to a reference source heated to a particular temperature, measured by the thermal unit Kelvin. The measurement can also be described as the “warmth” or “coolness” of a light source. Generally, sources below 3200K are considered “warm;” while those above 4000K are considered “cool” sources.

CONSTANT WATTAGE AUTOTRANSFORMER (CWA) BALLAST
A popular type of HID ballast in which the primary and secondary coils are electrically connected.

CONTRAST
The relationship between the brightness or luminance of an object and its background.

CRI
(SEE COLOUR RENDERING INDEX)

COMPACT FLUORESCENT LAMP (CFL)
A small fluorescent lamp that is often used as an alternative to incandescent GLS lamps. The lamp life is 4 to 10 times longer than incandescent lamps, and is some 3-5 times more efficient. Known generally as CFL lamps, and available in many versions. All require a ballast, which may be integral with the lamp or separate with a bayonet cap (BC) or Edison screw (ES) base.

CYCLING
Discharge lamps may sometimes cycle on and off towards the end of their life. It is an undesirable situation which may damage control gear, and most lamp and gear circuits protect against it. It may be due to incorrect lamps, improper voltage being supplied, or high ambient temperature around the luminaire.

COLOUR SPECTRUM
All wavelengths perceived by human sight, usually measured in nanometers (nm).

CONFORMAL PHOSPHOR COATING
Patented process that uniformly coats the LED with phosphor. This eliminates the blue-ring effect common to other white LEDs and delivers the consistent white colour throughout the light beam.

COOL WHITE
A description of light with a correlated colour temperature between 5000K and 7500K, usually perceived a slightly blue.

CORRELATED COLOUR TEMPERATURE (CCT)
The phrase use to describe the temperature at which a Planckian Black Body Radiator and an illumination source's appear to match, usually specified in Kelvin (K).

DICHROIC COATING
Type of coating on the inner surface of mirror or lamp which consists of several layers of very thin optical materials. The coating transmits selected colours, and reflects others. Applied to incandescent lamps, the technique allows heat energy to be reflected back onto the filament, effectively allowing the filament to run at a lower power.

DIFFUSE REFLECTOR
A material which scatters light as it reflects it.

DIFFUSER
A translucent piece of glass or plastic sheet that shields the light source in a fixture. The light transmitted throughout the diffuser will be redirected and scattered.

DIRECT GLARE
Glare produced by a direct view of light sources. Often the result of insufficiently shielded light sources.

EFFICACY
A metric used to compare light output to energy consumption. Efficacy is measured in lumens per watt. Efficacy is similar to efficiency, but is expressed in dissimilar units. For example, if a 100–watt source produces 9000 lumens, then the efficacy is 90 lumens per watt.

EFFICIENCY
A metric for luminaire performance. Efficiency is usually the ratio of the amount of light being directed out of the luminaire, in lumens, divided by the total light created by the lamp source. Comparisons for floodlighting should primarily include Beam Efficiency and Field Efficiency.

ELECTRONIC BALLAST
A ballast that uses semi-conductor components to increase the frequency of fluorescent lamp operation, typically in the 40+ kHz range. Watts loss is low, and fluorescent lamp efficacy is also increased due to high frequency operation. Used also for small HID lamps.

ELECTRONIC DIMMING BALLAST
A variable output electronic fluorescent ballast.

ELECTROMAGNETIC INTERFERENCE (EMI)
Interference caused by electrical components or discharge lamps may affect the operation of communication equipment. It is controlled by various methods in lighting circuits. The Australian Communications Authority has set strict limits for EMI, and all luminaries, except incandescent ones, must by law conform and carry the Regulatory Compliance Mark (RCM, known as the "C-Tick") as proof of compliance.

FIELD EFFICIENCY
The percentage difference between the field lumens and the rated lamp lumens.

FIELD LUMENS
Accumulated total lumens within the “field” designated by the 10% maximum candela measurement.

FOOTCANDLE (FC)
The English unit of measurement of the illuminance (or light level) on a surface. One footcandle is equal to one lumen per square foot.

FOOTLAMBERT
English unit of luminance. One footlambert is equal to 1/p candelas per square foot.

FLUORESCENT LAMP
Is a tubular lamp filled with mercury vapour at a low-pressure, and a small amount of an inert gas such as argon or krypton to aid starting and arc regulation. Electrodes are sealed into each end, and the light produced by the discharge is predominantly in the ultra-violet region. The inside of the tube is coated with fluorescent powders or phosphors, which the ultraviolet light excites to produce visible light. A wide range of colours and efficacies is available using different phosphors, individually or in combination.

GLARE
The effect of brightness or differences in brightness within the visual field sufficiently high to cause annoyance, discomfort or loss of visual performance.

HID
Abbreviation for high intensity discharge. Generic term describing mercury vapor, metal halide, high pressure sodium, and (informally) low pressure sodium light sources and luminaires.

HIGH POWER FACTOR
A ballast with a 0.9 or higher rated power factor, which is achieved by using a capacitor.

HIGH PRESSURE SODIUM LAMP
A high intensity discharge (HID) lamp whose light is produced by radiation from sodium vapor (and mercury).

HOT RESTRIKE
The re–striking or re–igniting the arc in an HID light source after a momentary power loss.

HALOGEN
(See QUARTZ HALOGEN LAMP)

HARMONIC DISTORTION
A harmonic is a sinusoidal component of a periodic wave having a frequency that is a multiple of the fundamental frequency. Harmonic distortion occurs when lighting equipment draws an irregular current waveform and can interfere with other appliances and the operation of electric power networks. The total harmonic distortion (THD) is usually expressed as a percentage of the fundamental line current. All discharge lamp circuits cause some harmonic distortion, and the maximum levels are prescribed in the various Australian Standards.

ILLUMINANCE
A photometric term that quantifies light incident on a surface or plane. Illuminance is commonly called light level. It is expressed as lumens per square foot (footcandles), or lumens per square meter (lux).

INDIRECT GLARE
Glare produced from a reflective surface.

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. LED and HID light sources range from 3000K to 7500K and higher.

LAMP LUMEN DEPRECIATION FACTOR (LLD)
A factor that represents the reduction of lumen output over time. The factor is commonly used as a multiplier to the initial lumen rating in illuminance calculations, which compensates for the lumen depreciation. The LLD factor is a dimensionless value between 0 and 1.

LENS
Transparent or translucent medium that alters the directional characteristics of light passing through it. Usually made of glass, neoceran or acrylic.

LIGHT LOSS FACTOR (LLF)
Factors that allow for a lighting system’s operation at less than initial conditions. These factors are used to calculate maintained light levels. LLFs are divided into two categories, recoverable and non–recoverable. Examples are lamp lumen depreciation and luminaire dirt depreciation.

LOW POWER FACTOR
Essentially, an uncorrected ballast power factor of less than 0.9 (SEE NPF)

LOW-PRESSURE SODIUM
A low–pressure discharge lamp in which light is produced by radiation from sodium vapor. Considered a monochromatic light source (most colours are rendered as gray).

LUMEN
A unit of light flow, or luminous flux. The lumen rating of a lamp is a measure of the total light output of the lamp.

LUMINAIRE
A complete lighting unit consisting of a lamp or lamps, along with the parts designed to distribute the light, hold the lamps, and connect the lamps to a power source. Also called a fixture.

LUMINAIRE EFFICIENCY
The ratio of total lumen output of a luminaire and the lumen output of the lamps, expressed as a percentage. For example, if two luminaires use the same lamps, more light will be emitted from the fixture with the higher efficiency.

LUMINANCE
A photometric term that quantifies brightness of a light source or of an illuminated surface that reflects light. It is expressed as footlamberts (English units) or candelas per square meter (Metric units).

LUX (LX)
The metric unit of measure for illuminance of a surface. One lux is equal to one lumen per square meter. One lux equals 0.093 footcandles.

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 i.e: Light
Levels:
Level 1 - The chip or die
Level 2 - The LED component
Level 3 - LED array; may include optics, heat sink and/or power supply
Level 4 - LED luminaire

MAINTAINED ILLUMINANCE
The average illuminance over the reference area at the end of the complete maintenance cycle, and is the minimum value to which the illuminance is allowed to fall.

MERCURY VAPOUR LAMP
A high intensity discharge (HID) lamp with a mercury filled arc tube producing UV light which excites the phosphor coating of the outer bulb. Moderate efficacy and colour rendering, and long lifetime.

METAL HALIDE
A type of high intensity discharge (HID) lamp in which most of the light is produced by radiation of metal halide and mercury vapours in the arc tube. Available in clear and phosphor-coated lamps. Has high CRI and efficacy.

OPTICS
A term referring to the components of a light fixture (such as reflectors, refractors, lenses, louvers) or to the light emitting or light–controlling performance of a fixture.

PAR LAMP
(parabolic aluminised reflector) An incandescent or metal halide lamp with a pressed glass parabolic reflector, minimising reflection losses behind the filament or arc tube. Lamps are available with flood or spot distributions.

PARABOLIC LUMINAIRE
A popular type of fluorescent luminaire with side reflectors and cross louvre blades having a parabolic section. The resultant light distribution produced by this shape provides reduced glare and good light output.

POWER FACTOR
In an electrical circuit, the ratio of the power in watts to the product of the r.m.s.. values of voltage and current. AS Wiring Rules and EMI regulations require correction to at least 0.8.

PREHEAT START
A fluorescent lamp circuit that uses a separate starter switch to heat the lamp cathodes before high voltage pulse is applied to start the lamp, as the starter contacts re-open. This is the most common circuit, but is not suitable for HF lamps.

PHOTOMETRIC REPORT
A photometric report is data describing the light (beam) distribution and efficiency of a luminaire. Reports are generated from laboratory testing and used for light level predictions or calculations; often from computer software.

QUARTZ HALOGEN LAMP
A gas-filled tungsten filament incandescent lamp with a lamp envelope made of quartz to withstand the high temperature. This lamp contains some halogens (namely iodine, chlorine, bromine, and fluorine), which through a recycling process effectively slow the rate of evaporation of the tungsten filament. Higher efficacies than similar wattage GLS lamps. Also, commonly called a tungsten halogen lamp.

REFLECTOR
The part of a light fixture that shrouds the lamps and redirects light emitted from the lamp.

REFRACTOR
A device used to redirect the light output from a source, primarily by bending the waves of light.

SEMI-SPECULAR
Term describing the light reflection characteristics of a material. Some light is reflected directionally, with some amount of scatter.

SPECULAR
Mirrored or polished surface. The angle of reflection is equal to the angle of incidence. This word describes the finish of the material used in some louvers and reflectors.

SPILL LUMENS
Accumulated lumens outside the ‘field’ boundary.

STARTER
A device used with a ballast to start preheat fluorescent lamps.

STROBOSCOPIC EFFECT
Where an alternating current supply is used with fluorescent and HID lamps, the light pulses at twice the supply frequency. This may cause a condition where rotating machinery or other rapidly moving objects appear to be standing still.

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.

TOTAL RATED LAMP LUMENS
The manufacturers rated lumen output per lamp.

TUNGSTEN HALOGEN LAMP
A gas–filled tungsten filament incandescent lamp with a lamp envelope made of quartz to withstand the high temperature. This lamp contains some halogens (namely iodine, chlorine, bromine, and fluorine), which slow the evaporation of the tungsten. Also commonly called a quartz lamp.

THERMAL MANAGEMENT
Controlling the operating temperature of the product through design, examples includes heat sinks and improved airflow.

THERMAL RESISTANCE (C/W)
A measure of the heat transfer capacity of the LED. Lower resistance is preferred.

ULTRA VIOLET (UV)
Invisible radiation that is shorter in wavelength and higher in frequency than visible violet light (literally beyond the violet light).

UNDERWRITERS' LABORATORIES (UL)
An independent organization whose responsibilities include rigorous testing of electrical products. When products pass these tests, they can be labeled (and advertised) as “UL listed.” UL tests for product safety only.

UNIFORMITY LEVELS
A metric used to determine the visual quality of illuminance; usually referred in terms of illuminance (footcandles/lux) either field measured or software calculated. Max/Min uniformity is the ratio of the maximum illuminance level reading divided by the minimum. Avg/Min uniformity is the ratio of the average of all illuminance levels divided by the minimum level.

VOLT
The standard unit of measurement for electrical potential. It defines the “force” or “pressure” of electricity.

VOLTAGE
The difference in electrical potential between two points of an electrical circuit.

WATT (W)
The unit for measuring electrical power. It defines the rate of energy consumption by an electrical device when it is in operation. The energy cost of operating an electrical device is calculated as its wattage times the hours of use. In single phase circuits, it is related to volts and amps by the formula: Volts x Amps x PF = Watts. (Note: For AC circuits, PF must be included.)
Many lamps come with rating in watts to indicate their power consumption. A light source with a higher lumen per watt value is more efficient.

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

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

ZENITH
The direction directly above the luminaire (180 angle).