A

Absorption
Process by which light is converted into heat when incident on or passing through a material.

Accent Beam
Accent beam provides sufficient illumination above the ambient level to attract attention. Five times the ambient is considered to be acceptable ratio. Can also provide modeling via directional positioning of the light source.

Accent Lighting
A synonym for display or highlighting

Accommodation
Focal adjustment of the eye, generally spontaneous, made for the purpose of obtaining maximum visual acuity at various distances.

Adaptation
The process which takes place as the eye, adjusts to the brightness of the colour of the visual field. The term is also used, usually qualified, to denote the final state of the process. For example, ‘dark adaptation’ denotes the state of the eye when it has become adapted to very low illuminance. Like somebody watching a film in a cinema.

Adaptation Level
The Level at which the eye will become adjusted in the steady state, in a given visual environment. For the purpose of lighting calculations, the level is taken arbitrarily as the arithmetic average of the luminance of the visual field for a given direction of view.

Air Boot
An air diffusing device that fits over an air-handling troffer and allows air to be supplied through the side slots of the fixture into the room; usually manufactured by HVAC equipment manufacturers and supplied under the mechanical subcontract.

Air-Handling
A type of troffer that can either supply air (heating or air conditioning) to a room, remove air from a room, or do both. Air handling units incorporate a floating door appearance by use of a black housing reveal.

Ambient Lighting
The, usually low, level of background light.

Ambient Luminescence
This is the base ingredient in a Lighting Vista without which the lighting system will be unsuccessful. It is not uniform general lighting but the casting of a gentle backdrop on top of which is the focal glow, the glitter, the wall lighting or the display lighting.

Ambient Temperature
Surrounding - the ambient temperature is the temperature of the air that surrounds the fixture in the room. A critical criterion for fixture selection especially in extreme temperature environments.

Amperage
A measure of the amount of current flowing in an electric circuit. Devices such as cables and dimmers are rated in terms of their maximum capacity in amps. Devices such as lamps or motors that consume electrical energy rated in terms of amperage required for proper operation. Amperage=Wattage/Voltage.

Ampere Hour
The constant supply of 1 ampere of current over the duration of one hour. Typically used in reference to batteries.

Analogue Dimmer
Dimmer controlled by a continuously variable low voltage signal, normally 0 to 10 volts DC.

Anodised
An electrolytic process for converting aluminium surface to aluminium oxide. Anodising creates a transparent finish that is physically part of the metal. Anodised finishes are generally colourless, but may be dyed in a variety of colours. The coating is hard and highly resistant to corrosion.

Apostilb
The metric unit of luminance. A uniform diffuser emitting 1lm/m2 1 asb=1/π cd/m2

Apparent Colour
Of a light source, subjectivity the hue of the source or of a white surface illuminated by the source; the degree of warmth associated with the source colour. Lamps of low correlated colour temperature are usually described as having a warm apparent colour, and lamps of high correlated colour temperature as having a cold apparent colour.

Approvals
Approval is given to products, which are type tested plus continued and regular factory surveillance, and of the quality management system employed.
See also ENEC Approvals.

Arc Tube
A tube enclosed by the outer glass envelope of a high intensity discharge lamp and made of clear quartz or ceramic that contains the arc stream.

Aspect Factor
A function of the angle subtended at a point by a length of a linear source, and of the axial distribution of luminous intensity from the source, used in the calculation of Illuminance at a point.

Assurance of Safety
Under the Consumer Protection Act 1987, it is unlawful to make, or hold in stock, or to offer for sale any electrical appliance that is unsafe. In order to give assurance that lighting products are safe, manufacturers have two options

1. To mark with the symbol of a third party approval authority. A mark of the guarantee endorsed by an independent testing authority. The mark guarantees that an independent test house has checked compliance with EN60 598 and that third party monitoring of the producing factory’s quality system has been undertaken.

2. Self Certification
The manufacture claims that the product is safe and is fit for purpose. The value of such a claim is directly related to the standing firm making it. In the case of IBL Lighting, all products are designed, developed and manufactured under the scope of the ISO 9001 quality systems that are registered and audited by independent third parties. See IBL Lighting’s 5-Year Guarantee.

ASTA
UK Approvals Body for plugs and other electrical equipment. Owner of the ASTA Diamond Mark denoting Approval by ASTA

Asymmetric Distribution
Non-symmetric distribution of light. In many cases, the luminous intensity may be more pronounced in one direction.

Average Rated Life
A value given to a light source

Azimuth Angle
The orientation angle horizontal plan usually measured clockwise from south to north.

B

Background Lighting
See ambient lighting.

Backlighting
The technique of setting in silhouette the profile of an object or display item by lighting from behind either by an illuminated panel or from display lighting from behind.

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 Efficacy Factor (BEF)
Value used to evaluate various lighting systems based upon light output and power input. Mathematical formula: Ballast Efficacy Factor equals Ballast Factor (percent value) divided by ballast Input Power (watts).

Ballast Factor (BF)
Measure of light output from lamp operated by commercial ballast, as compared to laboratory standard reference ballast.

Ballast Hum
Sound generated by the vibration of laminations in the electromagnetic field that transforms the current for discharge lamp use. Since electronic ballasts do not utilise large laminated coils, they operate with lower sound levels as compared to core & coil ballasts.

Ballast Losses
Power, which is supplied to ballast but is not converted into lamp energy. Ballast loss is dissipated as heat.

Ballast Lumen Factor
The ballast lumen factor (BLF) is the ratio of the light output of the lamp when the ballast under test is operated at its design voltage compared with the light output of the same lamp operated with appropriate reference ballast supplied at its rated voltage and frequency

Battery
Portable container of a cell or cells carrying an electric charge, as a source of current. Can be used for supplying emergency lighting during mains failure.

BC
Bayonet Cap (lampholder or lamp cap

Beam Angle
Angle of light spread to which the intensity witch is equal to 50% of the peak value.

Bollard
A type of architectural outdoor luminaire that is a short, upright ground-mounted unit typically used to provide cut-off type illumination for walkways, forecourts, steps, or other pathways.

Bridge Rectifier
Full wave bridge rectifier converts the ac mains supply to the dc required by the electronic ballast.

Brightness
What the eye sees, according to the Adaptation State. Not to be confused with luminance, which is what the light meter, reads.

Brushed Aluminium
A non-specular aluminium finish grainy in appearance.

BSi
British Standards Institution

BSi Committees

JPEL/64 - Installation Rules (IEE Wiring Regulations)
PEL/23 - Electrical Accessories
CPL/34/ - Lighting
CPL/34/1 - Lamps
CPL/34/2 - Lampholders
CPL/34/4 - Luminaires

Burning Position
Normally specified by the lamp manufacture, who will indicate the burning position cap up cap down or horizontal.

BZ Classification
British Zonal Classification System. A system for classifying luminaires as described in CIBSE Technical Memorandum No 5. The BZ class number (e.g. BZ3) denotes the classification of a luminaire in terms of the flux from a conventional installation directly incident on the working plane, relative to the total flux emitted below the horizontal (direct ratio).

C

Candela (CD)
The SI unit of luminous intensity, equal to one lumen per steradian, describes the intensity of a light source in a specific direction.

Candle Power
The light output in a given direction per angle unit. Candela (cd)

Capsule Lamp
A small extra low voltage lamp that normally fits into a luminaire with its own reflector. Low pressure and UV block types can be used without a safety shield

Catenary Luminaire
A luminaire specifically designed to be suspended from a cable and used for major road lighting schemes where with the main beam axes at right angles to

Cavity Index
A term, indicating the proportion of boundary surfaces, used in determining the effective reflectance’s of room surfaces for interior lighting design: defined for cavity of length L width W and depth d as LW/d (L+W).

CCA
CENELEC Certification Agreement. The scheme offers mutual recognition between European certification bodies for testing and ongoing product/factory surveillance of electrical and electronic products. BSI is a signatory to the agreement, which is accepted throughout the EC, EFTA and much of Eastern Europe.

CCL
Climate Change Levy (Introduced by Government in April 2000)

CE
European Community conformity mark.
European Community mark denoting that the product meets the manufacturers claim of conformity with the essential requirements of European New Approach Directives applicable to that product. At this time, Directives in place applicable to general lighting products and requiring the CE mark, are the Low Voltage Directive; the Electromagnetic Compatibility Directive and the Energy Efficiency of Ballasts for Fluorescent Luminaires Directive.

CE marking requirements are detailed in the applicable Directive and can vary from Full third party verification of product and quality systems to manufacturer’s self certification. But beware! If false claims are made prosecution could follow.

CELMA
Federation of National Manufactures for Luminaires and Electrotechnical Components for Luminaires

CENELEC
European Committee for Electrotechnical Standardization and is responsible for issuing Electrical Standards

Caring & cleaning your fittings and lamps
Please be certain to turn off the power and allow fixtures or lamps to cool down completely prior to attempting any cleaning or maintenance. Polished metal surfaces can be dusted using a soft dry cloth, or carefully cleaned with a slightly damp cloth. Never rub the finish excessively or use any abrasives or chemical cleaners as they can damage the finish.Remove glass shades from fixtures before applying any liquid to them. Please clean glass fixtures with a household glass cleaner or mild soapy water and then wipe dry.
Do not scrub glass with any abrasive material as this can cause scratches and imperfections. All glass products are not dishwasher safe. Make sure that all parts of the lamp / fitting are 100% dry. If not sure do not re connect to the mains power, discard the fitting of seek advice from an electrician.

Never allow electrical componebts to come in to contact with water or other liquids.

CFL
Compact Fluorescent Lamp

CFL Downlighters
Downlights designed for compact fluorescent lamps (CFL’s), or CFL downlights, are specified increasingly often as a way to reduce energy and maintenance costs.

CFL’s require less power than incandescent lamps to produce comparable light output and have average rated lamp life of 10,000 hours (h) compared with 1000 h for incandescent lamps. A screwbase CFL can save energy compared with an incandescent lamp if both are installed in similar incandescent downlights, but the light distributions may not be the same because the optical characteristics of CFL’s and incandescent lamps differ.

Chroma
The degree of saturation of a particular colour – low chroma means a pastel colour, high chroma means a saturated colour. The colourfulness of an area judged as a proportion of the brightness.

Chromaticity
The colour quality of stimulus usually defined by co-ordinates on a plane diagram in the CIE colourimetric system (IE Publication 15) or by the combination of dominant wavelength and purity

CIBSE
The Chartered Institute of Building Service Engineers

Circuit
A completed path of electrical elements includes the electric source, the wiring and the load.

Class I
Luminaires in this class are electrically insulated and provided with connection with earth. Earthing protects the user from the dangers of exposed metal parts becoming live in the event of a failure of the basic insulation.

Class II
These types of luminaire are designed and constructed so that protection against electric shock does not rely on basic insulation only. This can be achieved by means of reinforced or double insulation. No provision for Earthing is provided.

Class III
Protection against electric shock relies on the supply of Safety Extra Low Voltage (SELV) and in which voltages higher than those of SELV are not generated (Max.50V ac rms. or below).

Clearance Distance
Regulation-specified minimum distances between current carrying components of different polarity or between current carrying components and the accessible housing surfaces (clearance: shortest distance through the air; creepage distance: shortest distance across a surface

Clour Temperature
Measured in degrees Kelvin e.g. 2700ºK is very warm, 6000ºK is very cool.
The temperature of a full radiator, which emits radiation of the same chromaticity as the radiator being considered.

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

Coffer
Recessed panel or domed ceiling structure

Colour Appearance
General expression for the impression received when looking at a light source

Colour Rendering
A general expression for the appearance of surface colours when illuminated by light from a given source compared, consciously or unconsciously, with their appearance under light from some reference source. Good colour rendering implies similarity of appearance to that under an acceptable light source, such as daylight.

Colour Rendering Index
A measure of the degree to which the colours of surfaces illuminated by a given light source conform to the same surfaces under a reference illuminant, suitable allowance having been made for the state of chromatic adaption. (CIE Publication 13.2). CRI is expressed as a number where 100 indicates that there is no colour shift.

Compact Fluorescent
Small fluorescent lamps from 5W to 57W that are sufficiently compact to emulate an incandescent lamp. The term also applies to TC-L lamps up to 55W. See compact lamps in lamp data table Section 2.

Cone
Photoreceptors in the retina containing light-sensitive pigments capable of initiating the process of photopic vision.

Cool Beam Lamp
See dichroic reflector lamps.

CSI Lamp
Sealed beam PAR64 HID Metal Halide Lamp

Cut-off angle
The angle in elevation above which no light is emitted.

D

DALI
Digital Addressable Lighting Interface
The new method involves using DALI protocol-based technology (i.e.digital control signals) to control electronic ballasts, controllers and sensors belonging to the system. Each system component has its own device-specific address, and this makes it possible to implement individual device control.

Digital addressable lighting interface (see IEC 929)

The DALI system offers 64 individual addresses, 16 group addresses and the ability to program each ballast with up to 16 scenes.

Daylight Compensation
A dimming system controlled by a photocell that reduces the output of the lamps when daylight is present. As daylight levels increase, lamp intensity decreases. An energy-saving technique used in areas with significant daylight contribution.

Daylight Factor
The illumination received at a point indoors, from the sky of known or assumed luminance distribution, expressed as a percentage of the horizontal illuminance outdoors from an unobstructed hemisphere of the same sky. Direct sunlight is excluded from both values of illuminance.

Diffuse Reflection
The process by which incident light is redirected over a range of angles from the surface on which it is incident. There is no regular (specular) reflection involved.

Diffuse Transmission
The process by which incident light, while being transmitted through an object, is redirected or scattered over a range of different angles. There is no regular transmission involved.

Diffused Lighting
Lighting in which the luminous flux comes from many directions none of which predominates.

Diffuser
A device used to alter the spatial distribution of radiation depending essentially on the phenomenon of diffusion. Usually glass or plastic sheet that shields the light source in a luminaire. The light transmitted throughout the diffuser will be redirected and scattered.

Dimmers / Dimming
The process by which lamps are dimmed from 100% to determined level not always zero. It is not possible to dim switch start or other standard fluorescent luminaires, which have conventional control gear. Luminaires that are required to be dimmed will need special control gear for this operation. This can be achieved in a number of ways either by conversion, using remote dimmable ballast or by using an integral dimming ballast.

Direct Glare
Glare produced by a direct view of light sources. Often the result of insufficiently shielded light sources. (See GLARE)

Direct Lighting
Lighting in which the greater part of the luminous flux from the luminaires reaches the surface (usually the working plane) directly, i.e. without reflection from surrounding surfaces. Luminaires with a flux fraction ratio less than 0.1 are usually regarded as direct.

Downlighters whether compact; LV or linear fluorescent louvre luminaires emit all light downward

Directional Lighting
Lighting a display object predominately from one direction. Directional lighting can be used to great effect in retail display windows or even exterior floodlighting, produces strong modelling/shadows

Disability Glare
Glare from, for example, facing a spotlight or bright sunlit window that impairs the ability to see.

Discharge Lamp
Fluorescent lamps are medium pressure discharge lamps but high-pressure lamps include Metal Halide, Ceramic Metal Halide, and High-pressure Sodium lamps. SON or SDW-T. See table A for variations.

Discharge Lamps
Can provide excellent luminous efficacy, long lamp life and colour rendering to meet a variety of lighting needs, in both interior and exterior applications - examples retail, terminal buildings, street lighting and floodlighting.

Discomfort Glare
Glare that does not impair the ability to see, but that will cause over time a certain subconscious discomfort.

Distortion
A harmonic is a sinusoidal component of a periodic wave having a frequency that is a multiple of the fundamental frequency. Harmonic distortion from lighting equipment 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. THD for 4-foot fluorescent ballasts usually range from 20% to 40%. For compact fluorescent ballasts, THD levels greater than 50% are not uncommon.

DLOR
The ratio of the total light output of a luminaire below the horizontal under stated practical conditions to that of the lamp or lamps under reference conditions.

Double Insulation
Insulation comprising both basic insulation and supplementary insulation

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

Downlighting
Spotlighting or highlighting is the art of lighting itself, objects exhibits; pictures lit by this method can produce dramatic visual effects. Sometimes a combination of beam spreads is used to create a truthful deception.

E

ECA
Electrical Contractors Association

Escape Route Lighting
Emergency lighting provided on a defined route to ensure that the means of escape from a point in a building to the final exit.

EEC dir
EEC directive

EEC or EC
European Economic Community

Efficacy
A term 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
Ratio of power supplied to wattage dissipated

EIEMA
Electrical Installation Equipment Manufacturers Association

Electroluminescence
Known commonly as panel lighting. In panel lighting, particles of phosphor are suspended in a thin layer of non-conducting material such as plastic. Electroluminescent (EL) Lamps are flat, flexible, cold illumination sources and very thin. They consist of a thin polyester sheet (0.75mm) which has a chemical process screen-printed onto its surface and a lead is attached. When an electrical current is applied to the polyester sheet the phosphor based chemistry illuminates. It can be powered by a battery supply to drive a small inverter suitable for a single element lamp. On large formats a programmable sequencing inverter powers the multi segment display. This inverter can be driven by any low voltage mains power pack.

Electromagnetic Ballast (Mag)
Ballast that uses a “Core & Coil” assembly to transform electrical current to start and operate fluorescent and high intensity discharge (HID) lamps

ELV
Extra low voltage: voltage range from (1V – 50V)

ELV lamps
Usually 12V, for which a transformer is required. The filament is much smaller than mains coiled coil filaments, which renders more accurate control of the produced light, as well as being more robust with extremely good life qualities

EMC
Electromagnetic Compatibility

Emergency Exit
An exit, which is intended to be used only during an emergency.

Emergency Lighting
Lighting provided for use when the main lighting installation fails.

EN
European Standard issued by CENELEC

ENEC
The ENEC Mark is a European Approvals owned by signatories to the scheme. BSi, BEAB ASTA are the current signatories. Other signatories comprise the Certification Bodies from other EU member states. The Mark is awarded by one of the signatories and recognised by each other signatory throughout Europe. It is awarded following satisfactory type test to the applicable European Standard and successful assessment of the quality management facilities in the factory of production. Annual assessment of the product and facilities is required. In the case of luminaires, the ENEC Mark is restricted to the application by European manufacturers. The Lighting Association can provide ENEC testing through BEAB.
BEAB i.e. British Electrotechnical Approvals Board

ENV
European Prestandard

ES
Edison Screw (lampholder or lamp cap)

Escape Lighting
The part of emergency lighting which is provided to ensure that all means of escape can be safely and effectively used at all material times.

EST
Energy Saving Trust The Energy Saving Trust (EST) was set up after the 1992 Earth Summit in Rio de Janeiro, to help reduce CO2 emissions in the UK. It is a non-profit organisation funded by governments and the private sector.

Exit
A way out which is intended to be used at any time whilst the premises are occupied.

Extra Low Voltage Lamp
A lamp, typically a halogen type that provides both intensity and good colour rendering. The lamp requires an SELV supply via a transformer. Popular types are dichroic reflector lamps rated at 12V 20-75W

Eye sensitivity
The human eye has different sensitivity at different wavelengths. The maximum eye sensitivity occurs at a wavelength of 555 nm

Eye Structure
A light sensitive organ of vision that can distinguish minute variations of shape, colour, brightness and distance. The brain rather than the eye perform the actual process of seeing. The function of the eye is to translate the light into patterns of nerve impulses that are transmitted to the brain.

Eyeball Fitting
As the name implies a luminaire, which rotates and adjusts in elevation and azimuth

F

FELV
An extra low voltage system in which not all of the protective measures required for SELV or PELV have been applied.

Fibre Optics
A system using a centralised light source serving much miniature light heads via a harness of fibre optic strings. Can be plastic or preferably glass. Ideal for hazardous areas or ground burial.

Filament
The tungsten coil that glows to incandescence when an electric current passes through it

Fill Light
A lighting design term, which describes a light source, or direction, which is secondary, or fills in after a primary or key light source has been established.

Final Exit
A terminal point of an escape route, beyond which point persons are no longer in danger from fire or any other hazard requiring evacuation of the building.

Fitting
See luminaire

Fixture
America terminology for luminaire

Flicker
A visible oscillation in the luminous flux.

Flood Beam
Reflector lamps and luminaires with in built reflectors having a beam spread of more than 60º

Floodlight
Normally an exterior luminaire that directs light to provide night time illumination – can be aimed in any direction and has weatherproof construction.

Fluorescent lamps
A lamp, which produces its light by a gases discharge that in turn, irradiates a phosphor coating inside the glass envelope or tube to produce light by fluorescence. Provide a much more dispersed light than ‘point’ sources such as incandescent, halogen or discharge lamps. This quality, along with their outstanding energy efficiency, make them ideally suited for lighting large open areas such as offices and industrial buildings. Standard fluorescent lamps use halophosphate lamp coatings. These lamps are used where low initial cost is the most important factor. However, higher performance lamps using triphosphor coatings, such as Polylux XL lamps, are now increasingly being used as they provide better colour rendering and significant energy savings.

More detail: These light sources consist of a glass tube filled with argon, along with krypton or other inert gases. When electrical current is applied, the resulting arc emits ultra violet radiation that excites the phosphors coated on the inner wall of the tube, causing them to radiate visible light

Fluorescent Switching
Frequent switching of fluorescent lamps can reduce their operational life. Although a lamp that is only switched on and off rarely will last longer, light output does fall in the latter stage of a lamp’s life.

Fluorescent Tubes T12, T8, T5
Refer to their diameter in eighths of an inch, i.e. 12/8 (38mm) 8/8 (26mm) 5/8(16mm) and respectively.

Flux
(Lumens) falling on to a surface

Flux Fraction
The proportion of luminous flux emitted from a luminaire in the upper hemisphere. (Upper and lower flux fraction).

Flux Fraction Ratio
The ratio of the upward luminous flux to the downward luminous flux from a luminaire. It is also the ratio of the upper flux fraction to the lower flux fraction and the ratio of the upward light output ratio to the downward light ratio.

Framing Projector
Spotlights with an optical shutter device to manually shape and focus the beam.

Frequency
Rate of alternation in an AC current. Expressed in cycles per second or hertz (Hz).

G

General Lighting
Lighting designed to illuminate the whole of an area uniformly without provision for special local requirements.

GLS
General Lighting Service

Goniophotometer
A device for measuring the directional pattern of light distribution from sources, luminaires, media and surfaces.

H

HazdousEnvironments
An environment in which a risk of fire or explosion exists

HF Inverter
This device is made up of a half-bridge fet inverter together with starting components and lamp control and detection circuit. It converts the dc voltage on the electrolytic capacitor to high frequency ac to operate the lamp, providing warm start for the lamp. It also monitors for lamps at end of life or with broken cathodes and shuts down the inverter if necessary.

High Bay
Pertains to the type of lighting used in industrial applications were the mounting height is probably above 6m.
Also describes the application itself

IP Ratting

ISO
International Standards Organisation is responsible for issuing non-electrical Standards

Isolux Diagram
A diagram showing contours of equal illuminance. Can be used to determine the direct illuminance on a plane.

J

K

Kelvin
A measurement of temperature. 1° F = 256° Kelvin. 1° C = 274° Kelvin. Used to measure colour temperature. The SI unit of temperature used to express colour temperature. The temperature in Kelvin (K) is approximately equal to the temperature in Celsius (°C) plus 273. This absolute scale was named after Lord Kelvin who was the first to define temperature thermodynamically in a way which was independent of any particular physical substance

Kick Reflector
A reflector, which is used to produce and asymmetrical beam distribution often used in retail wall lighting. See wall washing.

Kitemark
Owned by BSI, the Kitemark is one of the most recognised and respected product marks in the UK. It demonstrates quality, safety and fitness for purpose.

L

LA
Lighting Association

Lamp
A device which converts electrical energy into light. Can be Tungsten filament, Fluorescent or HID.

Lamp Darkening
Through life, some darkening of the arc tube will occur due to the deposits of electrode material on the inside wall surface. This is quite normal with lamp ageing and cannot be avoided. Other causes are radiated heat reflected back onto the arc tube or poor luminaire design allowing excessive heating of lamp heating.

Lamp Flicker
Rapid strobe-like effect occurring in many fluorescent lamps. It is virtually unrecognisable in lamps operated by electronic ballasts due to their high frequency operation.

Laser
A device, which produces pencil, thin beams of coherent monochromatic light. Used primarily for special effects, lasers combined with beam splitters, scanners, and mirrors can be used to create a variety of three-dimensional images in fog or similar atmosphere. A laser and scanning system connected to a computer controller can be used to project complex animation effects.

Lay-in-Troffer
Usually a fluorescent luminaire 1200x600mm that sits or lays into a ceiling grid.

LDL
Lamps vary in flux output, both between themselves and through their operating lives. The lighting design lumens is a nominal value which representative of the average light output of each type or size of lamp throughout life.

Lead Lag
Types of 2-lamp ballast (used in both H.I.D. and fluorescent fixtures) so that one lamp is inductively controlled and the other is capacitively controlled, resulting in inherently high power factor (HPF).

Leading Edge Control
In the case of a phase cutting leading edge dimming the sinusoidal mains voltage in the negative and positive half is “chopped” at an angle in ascending proportion of the sinusoidal half wave. The higher the angle is set at the dimmer’s controller, the lower the voltage and thus the lamps output.

LED
Light-emitting Diode.
Ultra-bright light-emitting diodes based on the quartenary material combination AlGaInP/GaAs cover half the visible spectrum, ranging from yellowish-green to red. Since its first developments in 1992, this technology has been undergoing continuous improvements to increase the efficiency of the LED. Progress in epitaxial technology and process engineering has been coupled with innovative chip design and packaging to raise the luminous efficacy of these devices. In late 2000, semiconductors developed a new class of surface-structured LED reaching luminous efficacies of 25-30 lm/W in orange and red. Although the light is internally produced with a high degree of efficiency, a large proportion is absorbed by the GaAs substrate used in these LED as the germinal nucleus for
Crystal-growth.
Engineers have now turned to highly advanced thin-film technology to solve this problem. The so-called "substrate-less” LED still use the GaAs substrate for crystal growth, but afterwards they function without the base material, which effectively becomes ballast. With this new technology the upper side of the LED is coated with a metal layer after the epitaxy process, after which it is bound onto a new, thin carrier. The original GaAs substrate can then be removed, leaving behind just the thin, light-generating layer. The intermediate metal film is partially alloyed, allowing the alloyed part to act as an electrical contact and the non-alloyed part as a highly-reflective mirror. This technique allows far more light to be emitted than conventional LED designs. Red LED (615nm) can achieve a luminous efficacy of more than 50 lm/W

LED WHITE
Luminescence conversion:
Previously, the only way to produce white LED light was by the additive colour mixing of the three basic colours using so-called MULTILED, i.e., three semiconductor chips (red, green and blue LED) had to be combined.
Today lamp manufacturers can produce white LED light with only a single chip. In luminescence conversion, only a blue LED is used, whose light stimulates a luminescent substance that emits yellow light. In interaction, the system produces the colour white.
This light is generated on the basis of a principle similar to that used in luminescent substance lighting. Depending on the composition of the luminescent substance, various white tones can be realised.

In the future, the synthesis of these complementary core competencies in semiconductor technology and lighting engineering will lead to new product solutions and even faster technological progress in the field of LED.

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

LIF
Lighting Industry Federation

Light
Light is a natural phenomenon, vital to our very existence, which we probably take for granted in every day life. But the quality and intensity of light around us totally affects our visual appreciation and understanding of our surroundings.

Light Meter
Or exposure meter, device use for the measurement of light intensity. See photocell.

Light Output
The total amount of light produced by a light source in the visual spectrum. Unit Lumen (lm) symbol F.

Light Source
A surface emitting light produced by the transformation of energy.

Lighting
Lighting is a dynamic and exiting synthesis of art and science. Working together with shape and form, light brings life to the managed environment.
Light is a language in itself, encompassing the entire field of human emotions - it can be harnessed to soothe, excite, enhance, inspire, befriend, and create a sense of community. Collected here are some notes about lighting theory and also about the use of light in a variety of applications.

Light-Output Data
The lumen output figures quoted are measured at 25°C in accordance with EN60081 and EN60901

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.

LLMF
The amount of light depreciation occurring during lamp life.

Local Lighting
Lighting designed to illuminate a particular small area, which usually does not exceed far beyond the visual task, e.g. desk light.

Louvre
A fluorescent reflector system that has a cross blade louvre set at right angles to the light source. Office lighting applications.

Low Power Factor
Essentially, an uncorrected ballast power factor of less than 0.9

Low Pressure Sodium Lamp
A low-pressure discharge lamp in which light is produced by radiation from sodium vapour. Considered a monochromatic light source (most colours are rendered as grey).

LSC
Luminaire support coupler. A means, comprising an LSC outlet and an LSC plug, providing mechanical support for the luminaire and the electrical connection to and disconnection from the fixed wiring installation.

Lumen (Unit:Lm)
Standard unit of luminous flux. Describes the quantity of light emitted by a light source or received by a surface. A small source, which has a uniform luminous intensity of one candela, emits a total of 4 lumens in all directions and emits one lumen within a solid angle. See steradian. The lumen rating of a lamp is a measure of the total light output of the lamp.

Luminaire
Apparatus which distributes, filters or transforms the light transmitted from one or more lamps and which includes all the live parts necessary for supporting, fixing and protecting the lamps, but not the lamps themselves, and where necessary circuit auxiliaries together with the means for connecting them to the supply.
See BS EN 60598-1

Luminous Efficiency
The ratio of the luminous flux emitted by a lamp to the power consumed by the lamp. When the power consumed by the control gear is taken into account this term is sometimes known as lamp circuit luminous efficacy and is expressed in lumens/circuit watts.

Luminous flux
The rate of flow of light. The unit of measure is the Lumen. One lumen may be defined as the light flux emitted in one unit solid angle by a one-candela uniform-point source. The lumen differs from the candela in that it is a measure of light flux irrespective of direction. The lumen is used to express a quantity of light flux: total output of a source, output within a specific angular zone, amount of absorbed light for example.

Luminous Intensity
Unit: Cd
Luminous intensity is a measure of how much flux is emitted within a small conical angle divided by the solid angle of the cone; and is expressed in candelas. The inverse square law states that the illuminance E=l/d2, the intensity of the light source divided by the distance squared. In other words, this is the total number of lumens from a surface emitted in a given direction.
In modern standards, the candela is the basic of all measurements of light and all other units are derived from it. Measurements are often taken at various angles around the source and the results plotted to give a distribution curve. Such a curve shows luminous intensity in any direction.

The intensity in candelas of a source averaged over all possible directions; is equal to the total luminous flux output by the source divided by 12.56637 (4 pi).

Lux
The metric unit of measure for illuminance of a surface. One lux is equal to one lumen per metre-squared metre.

LV
Low voltage: voltage range from 50V – 1000V. Should not be confused with extra low voltage.