'A' TYPE BULB: The bulb shape of the common pear-shaped GLS incandescent lamp.

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.

BALLAST: Device used to operate fluorescent and HID lamps. The ballast controls the lamp current during operation, and may assist in the lamp starting process.

COLOUR RENDERING INDEX (CRI): A CIE scale used to indicate the colour rendering accuracy of a light source compared to a reference source of the same colour temperature, and is the average for eight standard colours, Ra8. Expressed on a scale of 1 to 100, a value of 100 indicates no distortion. A low CRI rating indicates that the colours of objects will appear distorted under that particular light source.

COLOUR TEMPERATURE: Colour temperature in Kelvin (K) is a term to describe the colour appearance of a light source, related to the colour of a black body radiator. If the colour point for the source does not lie on the black body locus, its colour temperature is given by the temperature of the black body which it most closely matches, and is its correlated temperature. 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.

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.

CONSTANT WATTAGE (CW) BALLAST: A type of HID ballast in which the primary and secondary coils are isolated, used principally in 110V countries. Watts losses are about twice those of an inductor type ballast on 240V or 415V supplies.

CONSTANT WATTAGE AUTOTRANSFORMER (CWA) BALLAST: Another type of CW ballast used principally in 110V countries. Watts losses are about twice those of an inductor type ballast on 240V or 415V supplies.

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

CRI: (See COLOUR RENDERING INDEX)

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.

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. (See GLARE)

DOWNLIGHT: A type of ceiling luminaire, usually fully recessed, where the light is directed downward. May feature an open reflector and/or shielding device.

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. (See System Efficacy)

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 luminaires, except incandescent ones, must by law conform and carry the Regulatory Compliance Mark (RCM, known as the "C-Tick") as proof of compliance.

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 discomfort or loss of visual performance, or both.

GLS: General lighting service, refers to standard incandescent lamps (tungsten filament).

HALOGEN: (See QUARTZ HALOGEN LAMP)

HALOPHOSPHATE: Phosphors based on calcium halophosphate, used for fluorescent tubes and mercury fluorescent lamps. They provide the common fluorescent lamp generic colours such as White, Warm White, and Daylight. Halophosphate lamps are relatively cheap, have good efficacies, and reasonable lumen maintenance characteristics.

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.

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

HIGH-BAY: An industrial lighting installation where the luminaire mounting height is at least 6m. May also describe the luminaires themselves.

HIGH OUTPUT (HO): A lamp or ballast designed to operate at higher currents (800mA) and produce more light than a normal fluorescent lamp of similar size.

HIGH POWER FACTOR: A circuit a 0.8 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 vapour (and mercury).

HOT RESTART or HOT RESTRIKE: Special control gear which allows some HID lamps to restrike immediately on restoration of supply after a momentary outage. Very expensive, and limited to fast sports and to spectator areas. Quartz-halogen lamps offer an alternative solution.

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

INDIRECT GLARE: Glare produced from a reflective surface.

INSTANT START: (Quick Start) An obsolete fluorescent lamp circuit that ignites some hot cathode lamp types within 1 second. In USA, cold cathode lamps with single-pin bases starting instantly with a high starting voltage from the ballast.

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 or acrylic.

LIGHT LOSS FACTORS (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 (LLD) and luminaire dirt depreciation (LDD).

LIFE-CYCLE COST: The total costs associated with purchasing, operating, and maintaining a system over the life of that system.

LOUVRE: Grid type of optical assembly used to control light distribution from a fixture. Can range from small-cell plastic to the large-cell anodized aluminium louvres used in parabolic fluorescent luminaires.

LOW LOSS BALLAST: A ferro-magnetic ballast designed to operate fluorescent lamps with a lower watts loss than a standard ballast.

LOW-PRESSURE SODIUM: A low-pressure tubular discharge lamp in which light at 589nm is produced by radiation from sodium vapour. A largely monochromatic light source, so colour rendition is very poor (most colours are rendered as grey). Very high efficacies, and mainly used in street lighting.

LOW-VOLTAGE LAMP: A lamp for use at lower than 240V supply, (typically 12V compact quartzhalogen). These lamps require the use of a transformer, with adds a further watts loss to the circuit. Popular lamps are MR11, MR16. Infra-red reflecting versions offer lower lamp wattages.

LUMEN: Unit of light output, or luminous flux. The lumen rating of a lamp is a measure of the total light output of the lamp, notionally measured at 100hr.

LUMINAIRE: A complete lighting unit consisting of a lamp or lamps, lampholders, optical elements to distribute the light, and the means for connection to a power source. Control gear, if required, may be integrated within the luminaire.

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.

LUX (lx): The metric unit of measure for illuminance of a surface. One lux is equal to one lumen per square metre.

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.

LPF (LOW POWER FACTOR): A ballast/lamp combination in which no capacitors have been added to correct the power factor, making it typically 0.5. Not permitted under EMI and AS Wiring Rules.

OCCUPANCY SENSOR: Control device that turns lights off after the space becomes unoccupied. May be ultrasonic, infrared or other type.

OPTICS: A term referring to the light-controlling components of a luminaire (such as reflectors, refractors, lenses, and louvres).

PAR LAMP: (parabolic aluminized 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.

PAR 36: A PAR lamp that is 36 one-eighths of an inch in diameter (102mm) with a parabolic shaped reflector (SEE PAR LAMP).

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.

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.

RAPID START (RS): An obsolete fluorescent lamp/ballast combination, requiring RS argon filled lamps. The ballast preheats lamp cathodes to start the lamp.

REFLECTOR: The part of a luminaire that redirects by reflection some light emitted from the lamp.

RECESSED: A luminaire which is recessed into the ceiling, so that the bottom of the light emitting elements is substantially flush with the ceiling.

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

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.

T12 LAMP: (USA) Industry term for a fluorescent lamp that is 12 one-eighths of an inch or 38mm in diameter. Other sizes are T10, T8 and T5 lamps.

TRIGGER START: (USA) Obsolete circuit commonly used with 15-watt and 20-watt straight fluorescent lamps. 

TRIPHOSPHOR: Fluorescent lamps with high efficacy use three rare earth phosphors to produce lamps that are referred to as tri-band or tri-phosphor lamps. There is some evidence to indicate that these lamps produce greater visual clarity at equal illuminance, and that equal visibility can be achieved at slightly lower light levels. These lamps generally have a higher colour rendering index than halophosphate lamps. Triphosphor lamps are frequently designated by three digits to indicate their CRI and colour temperature. They have excellent lumen maintenance characteristics.

TUNGSTEN HALOGEN LAMP: See QUARTZ HALOGEN LAMP.

WATT (W): The unit for measuring electrical power, 1 watt = 1 joule/sec. 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.)