Encyclopedia Of Light

Encyclopedia Of Light

The Complete Encyclopedia Of Light A - Z


Accent Lighting

Accent lighting is mainly decorative, intended to highlight pictures, plants, or other elements of interior design or landscaping. Another form of accent lighting is a lighting 'wash' where a broad angled spread of light covers the illuminated area.

Ampere/Amp (A)

An ampere is the unit of electric current. It is named after André-Marie Ampère (1775-1836), French mathematician and physicist, considered the father of electrodynamics. In practical terms, the ampere is a measure of the amount of electric charge (-e) passing a point per unit time. Around 6.241 × 1018 electrons passing a given point each second constitutes one ampere.


Device used with high or low pressure discharge lamps to limit, stabilize and regulate the current in the discharge.

The base of a lamp refers to the the part of the lamp that makes electrical connection with the fitting. These include: E14 (14mm Edison Skrew), E27, E40, B15 (15mm Bayonet), B22, R7s, G4, G9, GU10, GU5.3 and many more.

Beam Spread/angle
The angle over which the luminous intensity drops to a stated percentage (normally 10 or 50%) of its peak intensity.

A visual sensation in which an area or object appears to emit more or less light than another.

A light bulb is the colloquial term used to describe the common GLS, Incandescent lamp, or tungsten filament lamp that the large majority of consumers in the 20th century are used to. It's shape is similar to that of a bulbous plant root.


Candela is the unit of measure of luminous intensity in a particular direction.

Ceiling light
A Ceiling light as the name suggests is a light that is mounted on the ceiling surface but is distinguished from Spotlights, Chandeliers and Pendants by the fact that there is no form of suspension as it is usually mounted flush with the ceiling. Usually these fittings are non directional as opposed to multi-directional spotlights.

A chandelier is a branched decorative ceiling-mounted light fixture with two or more arms bearing lights. Chandeliers are often ornate, sometimes containing dozens of lamps and complex arrays of glass or crystal prisms to illuminate a room with refracted light.

Electrical Class refers to the type of insulation a light fitting requires. Class 0 appliances have no protective-earth connection and feature only a single level of insulation and were intended for use in dry areas. In most countries, the sale of Class 0 mains-voltage appliances is prohibited today, as a single fault could cause an electric shock or fire. The International Electro technical Commission is in the process of removing provisions for Class 0 devices from its standards. It can be expected that the Class 0 concept will eventually disappear from the international market, in favour of Class II devices. Class 1 insulation requires that the metal body and other exposed metal parts of the device is connected to earth via a ""grounding"" wire (usually yellow/green) which is earthed at the main service panel; but only basic insulation of the conductors is needed. This equipment is easily identified by a third pin on the power plug for the grounding connection.

Class 2 insulation means that the device is double insulated. This is used on some appliances such as electric shavers, hair dryers and portable power tools. Double insulation requires that the devices have both basic and supplementary insulation, each of which is sufficient to prevent electric shock. All internal electrically energized components are totally enclosed within an insulated body that prevents any contact with ""live"" parts and hence does not require a safety connection to electrical earth. In the EU, double insulated appliances all are marked with a symbol of two squares, one inside the other. A Class III appliance is designed to be supplied from a SELV (Separated or Safety Extra-Low Voltage) power source. The voltage from a SELV supply is low enough that under normal conditions a person can safely come into contact with it without risk of electrical shock. The extra safety features built into Class I and Class II appliances are therefore not required. For medical devices compliance with Class III is not considered sufficient protection.

Colour Rendering Index
The Colour Rendering Index is a reference to the degree to which a light displays the true colour of illuminated objects. A lamp with a high Colour rendering index accurately shows an items true colour while a low Colour Rendering Index creates an appearance that all the colours appear similar.

Colour Temperature
A measure of colour appearance of a light source and expressed in degrees Kelvin.

Compact Fluorescent (CFL)
A compact fluorescent lamp (CFL) or energy saving lamp is a type of fluorescent lamp. Many CFLs are designed to replace an incandescent lamp and can fit into most existing light fixtures formerly used for incandescents. Compared to general service incandescent lamps giving the same amount of visible light, CFLs use 80% less power and have a longer (6X) rated life. Like all fluorescent lamps, CFLs contain mercury, which complicates their disposal. CFL's radiate a different light spectrum compared with that of incandescent lamps. These colours include cool and warm white.

Components are the electrical hardware used to make up a light fitting.


DALI (Digital Addressable Lighting Interface) is a method of controlling electronic control gear for fluorescent lamps using digital signals. Unlike analogue brightness controls, DALI enables each luminaire to be controlled individually. It can be easily integrated in a building management system. Individual addressing means that not only the luminaires can be controlled but they can provide feedback messages so they can be operated in versatile energy-saving arrangements.

DB Board:
A distribution board (or panel board, breaker panel, or circuit breaker) is a component of an electricity supply system which divides an electrical power feed into subsidiary circuits, while providing a protective fuse or circuit breaker for each circuit, in a common enclosure. Normally, a main switch, and in recent boards, one or more Residual-current devices or Residual Current Breakers with Over current protection, will also be incorporated.
Diffused Lighting
Lighting in which the light on the working plane or on an object is not predominantly from another direction.

A reflecting of transmitting medium in which the light is so scattered as to give approximately uniform luminance in all directions.

A device in the electrical supply circuit for varying the luminous flux of lamps

Dimmable lighting systems were developed originally to meet the need for lighting that was easier on the eye. To an increasing extent, these systems are now also being used for cost saving reasons. Users can control the lighting with remote controls and switches, or control circuits with daylight sensors can be used. Leading edge phase dimming is used for low voltage tungsten halogen lamps operated with magnetic transformers. Trailing edge phase dimming is generally used for those lamps operated with electronic transformers. Compact fluorescent lamps (dimming range 3% to 100%) and fluorescent tubes (dimming range 1% to 100%) with electronic control gear are dimmed via a 1-10 V interface. Cables can either be laid separately (recommended for cable lengths > 100 m) or together, provided the requirements of wiring regulations are met.

Directional Lighting:
Lighting in which the light on a working plane or object is predominantly from a particular direction.

Discharge Lamp:
Gas-discharge lamps generate light by sending an electrical discharge through an ionized gas, i.e. a plasma. The character of the gas discharge critically depends on the frequency or modulation of the current. Typically, such lamps use a noble gas (argon, neon, krypton and xenon) or a mixture of these gases. Most lamps are filled with additional materials, like mercury, sodium, and/or metal halides. In operation the gas is ionized, and free electrons, accelerated by the electrical field in the tube, collide with gas and metal atoms. Some electrons circling around the gas and metal atoms are excited by these collisions, bringing them to a higher energy state. When the electron falls back to its original state, it emits a photon, resulting in visible light or ultraviolet radiation. Ultraviolet radiation is converted to visible light by a fluorescent coating on the inside of the lamp's glass surface for some lamp types. The fluorescent lamp is perhaps the best known gas-discharge lamp. Gas-discharge lamps offer long life and high light efficiency, but are more complicated to manufacture, and they require electronics to provide the correct current flow through the gas.

Down lighting:
Down-lighting is most common lighting method, with fixtures on or recessed in the ceiling casting light downward. This tends to be the most used method, used in both offices and homes. Although it is easy to design it has dramatic problems with glare and excess energy consumption due to large number of fittings.

A downlight is a light fixture that is installed into a hollow opening in a ceiling. When installed it appears to have light shining from a hole in the ceiling, concentrating the light in a downward direction as a broad floodlight or narrow spotlight. There are two parts to recessed lights, the trim and housing. The trim is the visible portion of the light. It is the insert that is seen when looking up into the fixture, and also includes the thin lining around the edge of the light. The housing is the fixture itself that is installed inside the ceiling and contains the lamp holder.


Electronic Ballast

Electronic ballasts employ transistors to alter mains voltage frequency into high-frequency AC while also regulating the current flow in the lamp. These ballasts take advantage of the higher efficacy of lamps operated with higher-frequency current. Efficacy of a fluorescent lamp rises by almost 10% at a frequency of 10 kHz, compared to efficacy at normal power frequency.


Electronic Control Gear

In contrast to the conventional wire wound control gear, ECG's operate at frequencies at or above 30kHz offering significant gains in efficiency. These gains include reduction in electrode losses and increases in luminous efficiency


Emergency Lighting

Lighting provided for use when the supply to the normal lighting fails. Escape Lighting is lighting that ensures an escape route will he highlighted when regular lighting fails. Standby Lighting is emergency lighting that enables certain activities to continue after regular power supply is interrupted.


Energy Efficiency

Energy efficiency is using less energy to provide the same level of energy service. For example, installing fluorescent lights and/or skylights instead of incandescent lights to attain the same level of illumination. Compact fluorescent lights use four fifths less energy and may last 6 to 10 times longer than incandescent light bulbs. Efficient energy use is achieved primarily by means of a more efficient technology or processes rather than by changes in individual behaviour.



A fan consists of a rotating arrangement of vanes or blades which act on the air. Usually it is contained within some form of housing or case. This may direct the airflow or increase safety by preventing objects from contacting the fan blades. Most fans are powered by electric motors.


Fibre Optic Lighting

An optical fibre is made up of the core, (carries the light pulses), the cladding (reflects the light pulses back into the core) and the buffer coating (protects the core and cladding from moisture, damage, etc.). Together, all of this creates a fiber optic. Fibres are used for illumination, and are wrapped in bundles so they can be used to carry light, thus allowing viewing in tight spaces. Typical application is in art galleries where there is low level lighting required and as little as possible UV radiation.



An apparatus to support an electric lamp and to control the light there from. The term Luminaire has the same meaning.




Impression of fluctuating luminance or colour.


Flood Light

A projector designed for floodlighting, usually capable of being aimed in any direction, and of weatherproof construction. A Flood light is a light that serves to 'wash' an area for security or decorative accent purposes.


Floor Light

A Floor Light is a free standing light fitting that usually stands head high and is used for general lighting; lighting a room; or for task lighting like reading.



Excitation of a phosphor or other material by ultra violet light.


Fluorescent Lamp

A Fluorescent Lamp is a gas discharge lamp using low pressure mercury vapour lamp in which almost all of the light is produced by the excitation of fluorescent phosphors on the inner surface of the lamp by ultra violet radiation. There are tubular, circular and 2D fluorescent lamps and also compact fluorescent lamps. The tube diameter is often expressed in eighths of an inch (e.g. T5 = 5/8'' = 16 mm).


Front lighting

Front lighting is also quite a common lighting method, but tends to make the subject look flat as its casts almost no visible shadows. Lighting from the side is the less common, as it tends to produce glare near eye level. Backlighting either around or through an object is mainly for accent.


Gas Discharge

A voltage is applied across two electrodes in a glass enclosure filled with inert gases, metal vapours and rare earths metals to produce an arc discharge. The direct radiation from the gaseous filler substances combines to produce the desired light colour. Examples: mercury vapour, metal halide and sodium vapour lamps.



General Lighting

General lighting or ambient light is neither task nor ambient and is intended for general illumination of an area. Indoors, this would be a basic lamp on a table or floor, or a fitting on the ceiling.




Glare is difficulty seeing in the presence of bright light such as direct or reflected sunlight or artificial light such as car headlamps at night or Stadium Lighting. Glare can be generally divided into two types, discomfort glare and disability glare. Discomfort glare results in an instinctive desire to look away from a bright light source or difficulty in seeing a task. Disability glare renders the task impossible to view, such as when driving westward at sunset. Disability glare is often caused by the inter-reflection of light within the eyeball, reducing the contrast between task and glare source to the point where the task cannot be distinguished.



Halogen Lamp

Halogen lamps operate in the same way as incandescent lamps and have a similar design. The small quantities of halogens (bromine, chlorine and iodine) or their compounds added to the filler gas almost entirely prevent bulb blackening from the evaporated tungsten (within a particular temperature range) so there is no associated loss in luminous flux during lamp life. By using quartz instead of glass, the bulbs of halogen lamps can be made much smaller and the pressure of the filler gas can be increased which enables the lamp life to be extended.



High Intensity Discharge Lamp (HID)

A high-intensity discharge (HID) lamp is a type of electrical lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with both gas and metal salts. The gas facilitates the arc's initial strike. Once the arc is started, it heats and evaporates the metal salts forming a plasma, which greatly increases the intensity of light produced by the arc and reduces its power consumption. High-intensity discharge lamps are a type of arc lamp. Compared with fluorescent and incandescent lamps, HID lamps have higher luminous efficacy since a greater proportion of their radiation is in visible light as opposed to heat. Their overall luminous efficacy is also much higher: they give a greater amount of light output per watt of electricity input.



High Pressure Sodium

A Sodium vapor lamp is a gas discharge lamp which uses sodium in an excited state to produce light. There are two varieties of such lamps: low pressure and high pressure. Because sodium vapor lamps cause less light pollution than mercury-vapor lamps, many cities that have large astronomical observatories employ them. these lamps have poor colour rendering.


Illuminance (E)

Measured illumination on a surface, the luminous flux per unit area of the surface. The unit of measurement in the lux (lx): E = F/A. An illuminance of 1 lx occurs when luminous flux of 1 lm is evenly distributed over an area of 1m2.



Incandescent Lamp

A lamp in which light is produced by heating a metal filament to incandescence. Incandescent lamps are classic thermal radiators in which electricity flows through a tungsten wire in an enclosed glass bulb filled with an inert gas or completely evacuated. The wire heats up to approximately 2600 to 3000 K making it glow white hot. Most of the radiation emitted is at the infra-red end of the spectrum. The main properties of an incandescent lamp, namely its luminous efficacy and life, are influenced largely by the filament temperature.


Infra Red Lamp

A heat lamp is an incandescent light bulb that is used for the principal purpose of creating heat. The spectrum of black body radiation emitted by the lamp is shifted to produce more infrared light. Many heat lamps include a red filter to minimize the amount of visible light emitted. Heat lamps are commonly used in shower and bathrooms to warm bathers and in food-preparation areas of restaurants to keep food warm before serving. They are also commonly used for animal husbandry. Lights used for poultry are often called brooding lamps. Aside from young birds, other types of animals which can benefit from heat lamps include reptiles, amphibians, insects, arachnids, and the young of some mammals.


IP Rating

Ingress Protection Rating. Protection against foreign objects and liquids.


No encyclopaedia items available for 'j'.



A temperature scale used to designate the colour temperature of a light source


Lamp Bases

see Base.



Lifetime or Average Life

The average life of a lamp is the average of the lives of individual lamps operated under standard conditions (50% failure = average rated life)



Light Colour

The light colour appearance of a lamp can be defined in terms of its Colour Temperature. There are three main colour groups: warm whites < 3300 K; neutral whites 3300 K - 5000 K and daylight whites > 5000 K. Despite having the same colour appearance, lamps may have very different colour rendering properties owing to the spectral composition of their light.



Light Emitting Diode (LEDs)

A light-emitting diode (LED)is a semiconductor light source. LEDs are used as indicator lamps in many devices, and are increasingly used for lighting. Modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness. The LED is based on the semiconductor diode. When a diode is switched on, electrons are able to recombine with holes within the lamp, releasing energy in the form of photons. This effect is called electroluminescence and the colour of the light is determined by the energy gap of the semiconductor. An LED is usually small in area (less than 1 mm2), and integrated optical components (lens) are used to shape its radiation pattern and assist in reflection. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact fluorescent lamp sources of comparable output.


Light Pollution

Light pollution, also known as photo pollution or luminous pollution, is excessive or obtrusive artificial light. The international Dark-Sky Association defines light pollution as: Any adverse effect of artificial light including sky glow, glare, light trespass, light clutter, decreased visibility at night and energy waste. Alternatively it can be described as the illumination of the night sky caused by artificial light sources, decreasing the visibility of stars and other natural sky phenomena. Also includes other incidental or obtrusive aspects of outdoor lighting such as glare, trespass into areas not needing lighting, use in areas where or at times when lighting is not needed, and disturbance of the natural night time landscape.



Light Source

The correct term to describe the production of artificial light by any means.




The unit of light flux (luminous flux ?) radiated by a light source. 1 lumen is the light contained per unit of solid angle and having an intensity of 1 candela in all directions.



Luminaire Efficiency

Luminaire efficiency is an important criterion in gauging the energy efficiency of a luminaire. It is the ratio between the luminous flux emitted by the luminaire to the luminous flux of the lamp (or lamps) installed in the luminaire.


Luminous Flux

Luminous flux (?) is all the radiated power emitted by a light source evaluated with the spectral sensitivity of the eye and the photometric radiation equivalent. Put another way Luminous Flux is the light output of a light source. It is measured in Lumens (lm).



Luminous Intensity

A measure of the illuminating power of a light source in a particular direction, independent of distance from the source. Unit = candela (cd)

Luminous intensity should not be confused with another photometric unit, luminous flux, which is the total perceived power emitted in all directions. Luminous intensity is the perceived power per unit solid angle.


Mercury Vapour

A mercury-vapour lamp is a gas discharge lamp that uses mercury in an excited state to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb. The outer bulb may be clear or coated with a phosphor; in either case, the outer bulb provides thermal insulation, protection from ultraviolet radiation, and a convenient mounting for the fused quartz arc tube. Mercury vapour lamps (and their relatives) are often used because they are relatively efficient. Phosphor coated bulbs offer better colour rendition than either high- or low-pressure sodium vapour lamps. Mercury vapour lamps also offer a very long lifetime, as well as intense lighting for several special purpose applications.


Metal Halide Lamp

A discharge lamp in which a major portion of the light is produced by excitation of a mixture of specific metallic vapours. Metal halide lamps are high pressure mercury lamps with added metal iodides or iodides of the rare earths (dysprosium (Dy), holmium (Ho) and thulium (Tm)) and complex compounds of caesium (Cs) and tin (Sn). They decompose in the core of the discharge arc and the metals can be excited to emit light with an intensity and spectral distribution that depends on the vapour pressure of the metal halides. The luminous efficacy and the colour rendering properties of the mercury discharge are significantly improved as the gaps in the mercury spectrum are filled by the spectral contribution of the other metals. Originally created in the late 1960s for industrial use, metal halide lamps are now available in numerous sizes and configurations for commercial and residential applications. Like most HID lamps, metal halide lamps operate under high pressure and temperature, and require special fixtures to operate safely. Since the lamp is small compared to a fluorescent or incandescent lamp of the same light level, relatively small reflective luminaires can be used to direct the light for different applications (flood lighting outdoors, or lighting for warehouses or industrial buildings).


Mounting Height

Mounting height refers to the suggested height that a light fitting should be mounted for optimum use.



Neon Lamp

A neon lamp is a gas discharge lamp containing primarily neon gas at low pressure. The term is sometimes used for similar devices filled with other noble gases, usually to produce different colors.


Operating Functions

Operating Functions refers to the modes of operation in Light fittings such as Fans, Emergency Lights, and Security Lights where there may be different speed, sensitivity, timing and activation settings.


Outdoor Light

An outdoor light is any light that is suitable for outdoor use and is protected by from the elements. This protection is observed by reference to it's IP rating which determines a fittings protection against liquid and foreign objects.



Pendant Light

A pendant Light is a light that is suspended from the ceiling by either a cord, cable or chain and usually consists of a shade or row of lamps. They distinguish themselves from chandeliers in that they don't usually have uniform radial arms as do chandeliers.


Philinea Tube

A Philinea tube is an Incandescent lamp that is cylindrical in form that is capped near each end however, these caps are not on the tips of the lamp (as with Strip lights) but rather on the side of the lamp.


The measurement of the light from light sources, luminaires and illuminated surfaces.

Photopic Vision

This vision typically occurs when the eye can see at around 30 lux where colour and detail are clear.


Project Lighting

Project lighting refers to lighting that is used in specific industries as task lighting. The combination of specifically designed Luminaires and specific lamps allows for the most efficant lighting for various tasks in industry and commerce.


QI Premium

QI Premium refers to the quartz used in the make up of linear halogen lamps.


Recessed Light

A recessed light is a light fitting that is usually mounted within the mounting surface. The housing is out of sight and only the surface and light source can be seen once installed.



Reflectivity is the fraction of incident radiation reflected by a surface. In general it must be treated as a directional property that is a function of the reflected direction, the incident direction, and the incident wavelength.



This is the property of materials to reflect light. There are different types of reflection, such as mirrored, mixed, fully diffused and irregularly diffused reflection. Indoor lighting uses diffused reflection almost exclusively. The reflective behaviour of a material is expressed by the reflection factor R. This is the ratio of the luminous flux reflected by the material to the luminous flux incident on the material (r= F/ F0). The reflection factor (reflectance) is specified in most cases for diffused incidence of light (rdif) or quasi-parallel incidence of light under 80 (r). In lighting technology the value mostly used is rdif. In theory, the maximum value for r and rdif is 1 (100%).



Reflectors make use of reflective surfaces to direct light where it is needed. They function on the basis of the law of reflection. They may be convergent or divergent. Most divergent reflectors have a white coating. The efficiency and the way in which light is distributed are primarily determined by the mounting depth of the lamp and dimensions of the reflector. Their shape has only a small influence. In the case of convergent reflectors, which nowadays are almost exclusively manufactured from polished anodised aluminium, the contours of the reflector play an important role. The following forms are the most common: Spherical reflectors return the light to the focal point; they are often used as additional reflectors for point-source lamps and spotlights; Elliptical reflectors send the rays of light to a second focal point. These reflectors enable a large quantity of light to be directed through small openings, provided small lamps with high luminances are used. The disadvantages are high temperatures at the focal point due to the concentration of the light and heat; Parabolic reflectors send the light from a light source out in a parallel beam. The maximum luminous intensity is determined by the luminance of the light source and the diameter of the reflector. Parabolic reflectors are used predominantly in spotlights and narrow angle luminaires.



Refraction is the change in direction of a wave due to a change in its speed. This is most commonly observed when a wave passes from one medium to another at an angle. Refraction of light is the most commonly observed phenomenon, but any type of wave can refract when it interacts with a medium.



Scotopic Vision

Scotopic Vision or Night Vision occurs at less than 10 lux where the eye can see large objects but no colour.


Security Light

A Security Light is a light that usually works in conjunction with a PIR (Passive Infra Red) sensor that is turned on in the case of any movement within the detection zone of the sensor. The sensors usually come with a variety of operating functions.



A Spotlight as the name suggests illuminates a specific 'spot'. This fittings usually mounted on the ceiling or wall are directional and usually have some form of reflector lamp to concentrate the beam of light.


Strip Light


A Strip Light is an incandescent lamp in a cylindrical form that is capped at both ends.


Table Light

A Table Light as the name suggests is a free standing light specifically for use on surfaces higher that the floor.


Task lighting

Task lighting is mainly functional and is usually the most concentrated, for purposes such as reading or inspection of materials in the work place. For example, anything ranging from a simple desk light to high lumen output lighting used in surgery.


Thermal Radiation

Current is passed through a wire to heat it to high temperature. The model here is the sun with its surface temperature of 6000K. Because it has the highest melting point of any metal (3683K), the element tungsten is best suited for this purpose. Examples: incandescent lamps and tungsten-halogen lamps.



Uplighting is a less common lighting method, often used to bounce indirect light off the ceiling and back down. It is commonly used in lighting applications that require minimal glare and uniform general illuminance levels. Uplighting (indirect) uses a diffuse surface to reflect light in a space and can minimize disabling glare on computer displays and other dark glossy surfaces. It gives a more uniform presentation of the light output in operation. However indirect lighting is completely reliant upon the reflectance value of the surface. While indirect lighting can create a diffused and shadow free light effect it can be regarded as an uneconomical lighting principle.


Volt (V)

The volt is defined as the value of the voltage across a conductor when a current of one ampere dissipates one watt of power in the conductor. It is named in honour of the Italian physicist Alessandro Volta (1745-1827), who invented the voltaic pile, possibly the first chemical battery.


Wall Light

A Wall light is a light mounted to the wall and comes in a variety of forms including upfacing half moons, decorative candle holder style fittings and flexible stem directional light.


The watt named after Scottish engineer James Watt is the unit that measures the rate of energy conversion. It is defined as one joule per second.



No encyclopaedia items available for 'x'.



No encyclopaedia items available for 'y'.


No encyclopaedia items available for 'z'.