Luminaires must be turned on manually but when a room is vacant the absence is detected and the luminaires are dimmed, after a pre-determined time they switch off. Absence detection is often used in classrooms, meeting rooms, offices and hotel rooms.
AC (Alternating Current)
An electric current that reverses its direction many times per second at regular intervals, typically used in power supplies.
Directional lighting to highlight a particular object or draw attention to a display item.
The system input power (in watts) for a lamp-ballast combination. Also known as Real Power.
The process by which the human eye adjusts to a change in light level.
Additive Colour Model
A type of RGB model which accounts for different proportions of red, green and blue light that result in different colours. In this model the combination of red, green and blue light produces white light.
A prolific LED technology used to produce produce red, orange and amber colours, contains Aluminium, Indium, Galium and Phosphorus. Hence it's namesake - Aluminium, "Al" - Indium, "In" - Galium, "Ga", and Phosphorus, "P".
Many spot and flood lamps are manufactured using a thin film of reflective aluminium deposited on the inside of the glass. Unlike dichroic reflectors, an aluminium reflector reflects both light and heat forwards out of the lamp.
An alloy of mercury with other metals. Some CFLs use mercury amalgam rather than standard mercury. An amalgam keeps mercury pressure in the discharge near its optimal value as lamp temperature changes. Amalgam lamps can produce more than 90 percent of maximum light output over a wide temperature range, but they can take longer to reach their full light output when started.
The general lighting present in an area, excluding task lighting and accent lighting but including general lighting and daylight streaming.
The temperature of the surrounding air that comes into contact with the lamp and ballast. Ambient temperature affects the light output and active power of fluorescent lamp/ballast systems. Each fluorescent lamp-ballast system has an optimum ambient temperature at which it produces maximum light output. Higher or lower temperatures reduce light output. For purposes of lamp/ballast tests, ambient temperature is measured at a point no more than 1 metre (3.3 feet) from the lamp and at the same height as the lamp.
American National Standards Institute (ANSI)
A non-profit organisation that develops voluntary consensus standards and conformity assessment systems for products, services, processes, systems, and personnel in the United States.
Named after the french mathematician and physicist André-Marie Ampère, the Ampere is a SI unit often abbreviated to 'Amp'. The Amp is used to measure the electric charge passing through an electric circuit per second.
Please see "American National Standards Institute" entry.
Circuitry used to detect and limit arcing of ballast output leads.
The diameter in the opening of a down light.
Apparent power is a measure of alternating current power that is computed by multiplying the root-mean-square current by the root-mean-square voltage.
The use or purpose of a lighting system. For example, high bay luminaires are ideal for industrial applications. The term can also refer in a general way to “application engineering” which deals with specific parameters and usage of light sources. (e.g. how to do a lighting layout, where to place fixtures and so on.)
Intense luminous discharge formed by the passage of electric current across a space between two electrodes.
A reflector, which distributes the light sideways providing uniform light distribution across the work area. There is no eye contact with the light source so there is no direct or indirect glare.
Circuitry used to restart the lamp without resetting the power of the ballast.
Average Maintained Illuminance
Illuminance averaged over a specified surface having being calculated with a maintenance factor.
Average Rated Life
The number of hours at which half of a large group of product samples fail under standard test conditions. Rated life is a median value; any lamp or group of lamps may vary from the published rated life.
Open area (anti-panic)
Areas of undefined escape routes in halls or premises larger than 60m2 floor area or smaller areas if there is any additional hazard such as use by a large number of people.
Please refer to L Ratings entry.
It can work with an older product or technology.
An auxiliary piece of equipment required to start and properly control the flow of current to gas discharge light sources such as fluorescent and high intensity discharge (HID) lamps. Typically, magnetic ballasts (also called electromagnetic ballasts) contain copper windings on an iron core. Electronic ballasts, commonly known as high frequency (HF) ballasts, are smaller and more efficient containing electronic components.
Ballast Efficacy Factor (BEF)
Defined as ballast factor divided by input watts. The value is used to evaluate various lighting systems based on light output and power input. The BEF can only be used to compare systems operating the same type and quantity of lamps. For example, a ballast with a ballast factor of 0.93 will result in the lamp emitting 93% of its rated lumen output. Ballasts with a lower BF results in less light output and also generally consumes less power.
Ballast Factor (BF)
The ratio of the light output of a fluorescent lamp or lamps operated by a commercial ballast as compared to a laboratory standard reference ballast. Ballast factor depends on both the ballast and the lamp type; a single ballast can have several ballast factors depending on lamp type.
Power or energy dissipated in the ballast as heat and not converted to lamp energy.
Ballast Lumen Factor (BLF)
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 the appropriate reference ballast supplied as its voltage and frequency.
Ballast Rated Life
The number of hours at which half of a group of ballasts fail under standard test conditions. Rated life is a median value of life expectancy; any ballast, or group of ballasts, may vary from the published rated life.
Typically, four adjustable shields that are attached to the face of the luminaire to reduce glare.
Secondary cells providing the source of power during mains failure.
The discharge capability of a battery. being a product of discharge current and time. expressed as Ampree Hours over a stated duration.
A style of lamp base that uses keyways instead of threads to connect the lamp to the fixture base. The lamp is locked in place by pushing it down and turning it clockwise.
The beam angle of a lamp is the angle at which the light is distributed or emitted. It is the angular dimension from the central part of the beam out to where the intensity is 50% of its maximum. The beam angle sometimes called “beam spread” is often part of the ordering code for the reflectorised lamps.
The direction in the centre of the solid angle which is bounded by directions having luminous intensities of 90% of the maximum intensity of a luminaire.
The width of a light beam, expressed in degrees. The beam of light from a reflector-type lamp (PAR, R, ER, or MR) can be thought of as a cone. The beam spread is the angular width of the cone. Common beam spreads are known as spot, narrow, narrow flood and flood.
To sort or classify light sources (such as light emitting diodes) into groups according to their luminous intensity or colour appearance.
Black Body / Black Body Radiator
An object that absorbs all electromagnetic radiation that falls on it and doesn’t reflect any light. A black body appears black.
Black Body Curve
A curve within a colour space, i.e. Planck Curve, describing the sequence of colours emitted by a black-body radiator at different temperatures.
A short, thick post with a light at its top, used for grounds and outdoor walkway lighting.
Common silicate glass is comprised of sand, sodium-carbonate and limestone, however, Borosilicate glass also includes boric oxide which makes the glass more expensive to produce and gives it certain characteristics. Borosilicate glass is more tolerable of thermal fluctuations; it does not expand and contract like common silicate glass. Also, it is more likely to shear as opposed to shatter. Borosilicate glass is typically used for lab equipment and is sometimes used for lenses in high-end lighting products.
This is a process where the fluorescent lamp is run at 100% of its power for a set period of time (usually 100 hours) to prevent premature failure. This is adopted when fluorescent lamps are to be dimmed.
The measure of luminous intensity of a source in a given direction. The term has been retained from the early days of lighting when a standard candle of a fixed size and composition was defined as producing one candela in every direction. A plot of intensity versus direction is called a candela distribution curve and is often provided for reflectorized lamps and for luminaires with a lamp operating in them.
The electrical connection and mechanical fixing for a lamp is often referred to either as a cap or base. Lamps use a wide variety of fittings, partly to meet the appropriate electrical and safety requirements and partly to ensure that luminaires can only accept the appropriate lamp (e.g. to prevent using low voltage lamps in mains fittings). Common caps for standard incandescent lamps include the ubiquitous 22mm “bayonet” fitting (otherwise known as “B22d” or “BC”) and the Edison Screw (or “ES”) fitting, named after the early pioneer in electric lamp development. To ensure compatibility between different manufacturers’ products, international standards for lamp bases have been agreed by the IEC under the IEC 60061 standard.
A device used in electric circuitry to temporarily store electrical charge in the form of an electrostatic field. In lighting, a capacitor is used to smooth out alternating current from the power supply on a high inductive load.
Metal filaments that emit electrons in a fluorescent lamp. Negatively charged free electrons emitted by the cathode are attracted to the positive electrode (anode), creating an electric current between the electrodes.
Chemical generator of electromotive force; typical cell types include lead-acid and nickel-cadmium.
Central Battery System
A system in which the batteries for a number of luminaires are housed in one location, usually for all the emergency luminaires in one lighting sub-circuit, sometimes for all emergency luminaires in a complete building.
CENTRAL BEAM CANDELA
Power emitted by a light source in a particular direction. A common candle emits light with a luminous intensity of roughly one candela.
Central Testing System (FM Wireless)
A system which a number of self-contained emergency luminaires and exit signs are able to communicate using radio technology to for a wireless network between fixtures and back to central control unit, for the purposes of enabling centralised testing control and maintenance of all devices on the system.
Central Testing Systems (BUS Wired)
A system in which a number of self-contained emergency luminaires and exit signs are connected via a DALI BUS cable back to a central control unit, for the purposes of enabling centralised testing control and maintenance of all devices on the system.
CHIP ON BOARD (CoB)
Refers to the semiconductor assembly technology wherein the microchip or die is directly mounted on and electrically interconnected to its final circuit board, instead of undergoing traditional assembly or packaging as an individual IC.
A term used to refer to a simple inductive ballast, typically a switch start ballasts.
Chromacity is the objective specification of colour, in terms of saturation and hue, independent of it's luminance.
The CIBSE (Chartered institute of Building Service Engineers)through the Society of Light and Lighting (SLL) produces several lighting guides for interior and exterior lighting, which gives lighting requirements for specific areas.
Abbreviated as CIE from the French title Commission International de l’Eclairage, the International Commission on Illumination is a technical, scientific, and cultural organization devoted to international cooperation and exchange of information among its member countries on matters relating to the science and art of lighting.
Discharge lamp designed to start without preheating the electrodes, for example ‘TL’S fluorescent lamp.
Cold Start Time
The amount of time from the application of ballast voltage to ignition of the arc discharge.
Standard Deviation of Colour Matching (SDCM); describing the difference between two colours, e.g. a differente of 1-3 SDCM is virtually imperceptible; a difference of 4 or more is readily visable.
Where uniformly illuminated objects are defined using three criteria: -
Hue: Describes the situation when the appearance of different colours is similar. (i.e. matching blues and pinks)
Lightness: Describes the spectrum of grey between black and white.
Chroma: Describes the degree of departure from grey of the same lightness and increasing colour (e.g. red, redder, vivid red).
An abstract mathematical model which allows colours to be represented as a group of values or colour components. Examples include, the RGB (red-green-blue) model, which uses three colour components. Another is the CMYK (cyan-magenta-yellow-black) model, which uses 4 colour components.
A general expression for the effect of a light source on the colour appearance of objects in conscious or subconscious comparison with their colour appearance under a reference light source.
Colour rendering index (CRI)
A rating index commonly used to represent how well a light source renders the colours of objects that it illuminates. For a CRI value of 100, the maximum value, the colours of objects can be expected to be seen as they would appear under an incandescent or daylight spectrum of the same correlated colour temperature (CCT). Sources with CRI values less than 50 are generally regarded as rendering colours poorly, that is, colours may appear unnatural.
The change in a lamp’s correlated colour temperature (CCT) at 40% of the lamp’s rated life, in Kelvin (K).
The ability of a lamp or light source to maintain its colour rendering and colour appearance properties over its life. The colour properties of some discharge light sources may tend to shift over the life of the lamp.
Correlated Colour Temperature (CCT)
A number indicating the degree of “yellowness” or “blueness” of a white light source. Measured in Kelvins, CCT represents the temperature an incandescent object (like a filament) must reach to mimic the colour of the lamp. Lamps with a warm (yellowish white) appearance, like incandescent lamps, have a CCT of 2700-3000K and are considered appropriate for domestic settings. Lamps of 4000K and above are considered ‘cool’ and are more appropriate for office and some retail applications. The higher the colour temperature, the whiter or bluer the light will be..
Combined Emergency Luminaire (Sustained)
Contains two or more lamps at least one of which is energised from the emergency supply and the remainder from the normal supply. The lamp energised from the emergency supply in a combined emergency luminaire is either maintained or non-maintained.
Compact Fluorescent Lamp (CFL)
The general term applied to fluorescent lamps that are single-ended and that have smaller diameter tubes that are bent to form a compact shape. Some CFLs have integral ballasts and medium or candelabra screw bases for easy replacement of incandescent lamps.
An abbreviated list of common ballasts that will provide the necessary circuitry for a photo sensor to operate correctly. Other ballasts may also be compatible; contact the photo sensor manufacturer for details.
The process of removing heat from an object via physical contact with other objects or materials, usually metals.
Material that surrounds and adheres to components and protects them.
The capacity to be connected to other appliances, facilities and the Internet.
Constant Light (For Daylight Harvesting)
Modern buildings are expected to maximise use of natural daylight, for people's comfort and wellbeing and to save energy. Daylight Harvesting is often used in rooms and spaces where natural daylight can provide some or all of the light required, and where the electric lights can be adjusted in response to varying ambient light levels. Constant light is often used in classrooms, offices, hospital treatment rooms and spaces with skylights.
Control of a light source’s intensity to practically any value within a given operating range.
Continuously variable signal
A signal that communicates data that can have a theoretically unlimited number of possible values between two end points. Examples include voltage, temperature, and illuminance.
Also known as luminance contrast, it is the relationship between the luminance of an object and its immediate background.
The process of removing heat from an object through the surrounding air.
A term loosely used to denote a colour temperature of around 4100 K.
An illuminance meter that measures the light level correctly; irrespective of the angle the light is coming from.
A property of a light source such that its luminous intensity in a particular direction is proportional to the cosine of the angle from the normal to the source.
Please refer to "Colour Rendering Index" entry.
Cut off angle
The angle of light distribution from a luminaire, measured upward from nadir, between the vertical axis and the first line at which the bare source (lamp) is not visible.
Colour of housing.
Lighting design for building interiors which uses daylight as a way of reducing energy consumption.
Unit of sound measurement.
Degree of polarization
A measure of the amount of light polarization ranging from 0 to 100 percent.
The amount of light that a luminaire or lighting installation delivers to a target area or task surface. This is typically measured in lux.
The amount of light that a lamp produces after it has operated for approximately 40% of its rated life. Also called "mean lumens".
Dichroic coating (dichroic filter)
A multi-layer coating that transmits certain wavelengths and reflects those not transmitted.
Dichroic Reflector (or Filter)
A reflector (or filter) that reflects one region of the spectrum while allowing the other region(s) to pass through. A reflector lamp with a dichroic reflector will have a “cool beam” i.e. most of the heat has been removed from the beam by allowing it to pass through the reflector while the light has been reflected.
Diffusers scatter the light from a luminaire in all directions. Most diffusers in commodity residential-grade luminaires are made of plastic, usually acrylic or polycarbonate.
A collection of evolving technologies that enables generation, collection, analysis, storage in real-time and data exchange.
DALI (Digital Addressable lighting Interface)
A digital communications protocol for the control and dimming luminaires and lighting systems, widely adopted throughout Europe.
Whether or not the lamp lumens can be varied while maintaining reliability.
DIMMABLE AVERAGE LIFETIME 10% FAILURE
Lifetime in hours, defined by reaching 10% failures (i.e. 90% survivors) when dimmed.
A device that provides the ability to adjust light levels by reducing the lamp current. Most dimming ballasts are electronic.
Dimming range in which the system will perform as specified.
Light emitted by a luminaire in the general direction of the task to be illuminated. The term usually refers to light emitted in a downward direction.
Light emitted upward by a luminaire.
A type of glare that causes a loss of visibility due to stray light being scattered within the eye.
A general term embracing both sodium and mercury vapour-filled lamps.
The sensation of annoyance or even pain induced by overly bright sources.
For light emitting diodes, a device that regulates the voltage and current powering the source.
DRIVER POWER FACTOR
Indicating how effective the driver converts electric current to useful power output.
Dynamic outdoor lighting
Outdoor lighting that varies light level or other characteristics automatically and precisely in response to factors such as vacancy or ambient lux levels.
A measurement of how effective the light source is in converting electrical energy to lumens of visible light. Expressed in lumens-per-watt (lm/w), this measure gives more weight to the yellow region of the spectrum and less weight to the blue and red region where the eye is not as sensitive.
The efficiency of a light source is simply the fraction of electrical energy converted to light, i.e. visible light produced for each watt of electrical power with no concern about the wavelength where the energy is being radiated.
EFFICIENCY RANGE MAX LOAD
Efficiency when operated at maximum power (not dimmed).
Electromagnetic interference (EMI)
The interference of unwanted electromagnetic signals with desirable signals. Electromagnetic interference may be transmitted in two ways: radiated through space or conducted by wiring. Luminaires need to comply with EMC requirements.
A continuum of electric and magnetic radiation that can be characterised by wavelength or frequency. Visible light encompasses a small part of the electromagnetic spectrum in the region from about 380 nanometers (violet) to 770 nanometers (red) wavelength.
A short name for a high frequency electronic ballast. Electronic ballasts use solid-state electronic components and typically operate fluorescent lamps at frequencies in the range of 25-35 kHz. The benefits are: increased lamp efficacy, reduced ballast losses and lighter, smaller ballasts compared to electromagnetic ballasts.
An electronic starter device for starting a discharge lamp (in particular a fluorescent lamp) which provides for the necessary preheating of the electrodes and / or causes a voltage surge in combination with the series ballast.
Emergency escape route lighting
That part of emergency escape lighting provided to ensure that the means of escape can be effectively identified and safely used at all times when the premises are occupied.
Lighting provided for use when the mains lighting installation fails.
European Order Code.
A route designated for escape to a place of safety in the event of an emergency.
Eye Safety Risk
Eye safety risk is one of a number of considered factors regarding photobiological risk, as outlined by BS EN 62471:2008. This standard outlines a class system by which lamps and lighting systems are classified according to their potential to cause photochemical or physiological harm to individuals. i.e. overexposure to infrared or ultraviolet radiation and retinal thermal harm.
A curve depicting the sensitivity of the human eye as a function of wavelength (or colour). The peak of human eye sensitivity is in the yellow-green region of the spectrum. The normal curve refers to photopic vision or the response of the cones.
The ability of a light source to render the same colours as a reference.
The angular dimension of the cone of light from reflectorized lamps (such as R and PAR types) encompassing the central part of the beam out to the angle where the intensity is 10% of maximum.
Field of view
The area covered by an occupancy sensor, often reported (for wall-mounted sensors) as a horizontal field of view or (for ceiling-mounted sensors) as the solid angle of the cone-shaped coverage area.
Metal tungsten wire heated by the passage of electrical current, used to emit light in incandescent lamps. In fluorescent lamps the filament is coated with emission mix and emits electrons when heated.
A complete lighting unit consisting of lamp or lamps and the parts designed to distribute the light, position and protect the lamp(s), and connect the lamp(s) to the power supply. (Also referred to as luminaire.)
A rapid and continuous change in light levels caused by the modulation of the light output from fluorescent lamps.
A luminaire used to light a scene or object to a level much brighter than its surroundings. Usually floodlights can be aimed at the object or area of interest.
A physical phenomenon whereby an atom of a material absorbs a photon of light and immediately emits a photon of longer wavelength. If there is a significant delay the phenomenon is called phosphorescence rather than fluorescence.
A high efficiency lamp utilising an electric discharge through inert gas and low-pressure mercury vapour to produce ultraviolet (UV) energy. The UV excites phosphor materials applied as a thin layer on the inside of a glass tube, which makes up the structure of the lamp. The phosphors transform the UV into visible light.
Forward Voltage (FV) is the Voltage an LED requires to operate. It is measured by calculating the voltage drop in a circuit before and after the LED module when the nominal current is flowing (provided the anode is more positive than the cathode).
A material with flame retardant properties often used for printed-circuit-boards (PCBs). Consists of fibreglass reinforced with epoxy laminate.
The number of times per second that an alternating current system reverses from positive to negative and back to positive, expressed in cycles per second or Hertz (Hz).
A colour gamut is formed by a specific set of colours rendered by the source and is also referred to as the gamut area. If a different set of colours is used the gamut area will be different.
An electric lamp that produces light from gas atoms excited by an electric current.
Lighting designed to illuminate the whole of an area uniformly, without provision of special lighting requirements.
The effect that occurs when lighting fixtures continue to glow when off due to residual voltage in their circuit.
Glare is the discomfort or impairment of vision, which occurs when the eye encounters more light than it can cope with.
Glow Wire Testing
Glow wire testing is an electrical safety test designed to evaluate the flame resistant properties of plastic materials used in electrical devices. Its purpose is to protect against the risk of fire from overheated or electrically energised parts which may cause the plastic material to ignite. This may occur in normal use, under reasonable abnormal use, malfunction or failure of the product. The glow wire simulates an over-heated part which then comes into contact with plastic materials.
GLS (General Lighting Service)
The general lighting service (GLS) lamp, or common light bulb, has a coiled filament contained within an envelope (bulb) of glass.
Also referred to as halo-phosphates. Phosphors are the white powder inside fluorescent lamps that fluoresces (emits visible light) when excited by the ultraviolet radiation produced by the mercury vapour that is energised by the electric arc sustained inside the lamp. Phosphors are used to achieve high efficacy, good colour rendering, and low lamp lumen depreciation. Halo-phosphors, however, are limited in their ability to provide a high colour-rendering index without sacrificing light output and are often mixed with other phosphors.
Halogen incandescent lamps are in the same family as standard incandescent lamps. The basic operating principle is the same, except that chemicals called halogens are introduced in the gas fill. When electricity passes through the lamp’s filament, it is heated until it glows and emits light. In this process, tungsten from the filament evaporates and, over the life of the lamp, causes the glass bulb wall to slowly blacken and the filament to disintegrate until the lamp fails. Halogens remove evaporated tungsten from the glass wall and redeposit it back onto the filament. As a result, tungsten does not build up on the bulb, so the light output does not degrade as rapidly.
A halogen lamp is an incandescent lamp with a filament that is surrounded by halogen gases, such as iodine or bromine. Halogen gases allow the filaments to be operated at higher temperatures and higher efficacies. The halogen participates in a tungsten transport cycle, returning tungsten to the filament and prolonging lamp life.
A measurement of the magnitude of voltage or current harmonics as compared with the amplitude of the fundamental frequency voltage or current.
Refers to components of the overall frequency, an integral multiple of the fundamental sine wave frequency.
Adding a material, usually metal, adjacent to an object in order to cool it through conduction.
Current or voltage operating frequency, equal to cycles per second.
Lighting designed for (typically) industrial locations.
High Frequency Ballast
Electronic ballast that operates the lamps above 20 kHz (20,000 cycles per second).
High-intensity discharge (HID)
An electric lamp that produces light directly from an arc discharge under high pressure. Metal halide, high-pressure sodium, and mercury vapour are types of HID lamps.
High Power Factor
A ballast whose power factor is corrected to 90% or greater by the use of a capacitor.
High-pressure sodium (HPS)
A high-intensity discharge lamp type that uses sodium under high pressure as the primary light-producing element.
The average density of luminous flux incident on a horizontal surface, measured in lux (lx).
Hot Restart Time
Time it takes for a High Intensity Discharge lamp to reach 90% of light output after going from on to off to on.
The attribute of a light source or illuminated object that determines whether it is red, yellow, green, blue, or the like.
An LED technology typically used to produce green, blue and white colour. Utilises Indium, Galium and Nitrogen. Hence it's namesake, Indium - "In", Galium - "Ga", and Nitrogen - "N".
A device that generates voltage pulses to start discharge lamps.
IK Rating (vandal resistance)
These ratings are used to classify the degree of protection provided by an enclosure against external mechanical impacts. Previously, this characteristic was indicated by an additional number added to the end of an IP rating – e.g. IP66(9), however the non-standardised and inconsistent use of this approach led to the development of the IK rating system.
The luminous flux density per unit surface area. Illuminance is measured lux (lumens/square metre).
A device, calibrated either in lux, which can measure illuminance at a location. (Also known as a light meter)
Emission of visible light by a heated material.
A light source, which generates light by using a thin filament wire (usually tungsten) heated to white heat by an electric current passing through it.
The method of lighting a space where most of the light reaches a surface, usually on a working plane, only after reflection off other surfaces such as walls and ceilings. The light scattered off the ceiling produces a soft, diffuse illumination for the entire area.
Induction lighting is essentially a fluorescent light without electrodes or filaments, which means that it has a longer life than standard lamps. Induction lighting is ideal for street lighting or cold environments.
Initial Light Output
The amount of light output from a lamp when it is new. For a metal halide lamp, ratings are made after 100 hours to allow the light-producing chemicals in the arc tube to deliver optimum performance.
Voltage, from the power line, which the ballast uses to power fluorescent lamps
Initial surge of current when an electrical device is turned on.
A method of starting fluorescent lamps in which the voltage that is applied across the electrodes to strike the electric arc is up to twice as high as it is with other starting methods. The higher voltage is necessary because the electrodes are not heated prior to starting. This method starts the lamps without flashing. It is more energy efficient than rapid or preheats starting, but results in greater wear on the electrodes during starting. The life of instant-start lamps that are switched on and off frequently may be reduced by as much as 25 percent relative to rapid-start operation. However, for longer burning cycles (such as 12 hours per start), there may be no difference in lamp life for different starting methods.
Intensity (luminous intensity)
the quantity which describes the power of a source or illuminated surface to emit light in a given direction. It is the luminous flux emitted in a very narrow cone containing the given direction divided by the solid angle of the cone. Expressed in candelas, or lumens per steradian.
Inverse Square Law
Formula for calculating lux levels in conjunction with cosine laws when a luminaire is considered as a point source.
IP (ingress protection) Rating
IP ratings, or Ingress Protection ratings, consist of a coding system which is used to classify the extent to which enclosures are susceptible to intrusion by solid foreign bodies, such as fingers or dust, and liquids. It’s purpose was to enable the industry to move away from inaccurate descriptions of enclosures i.e. splash proof. This IP Rating classification method was outlined by the International Electrotechnical Commission (IEC Standard 60529), and is recognised in most European countries.
A common misconception about IP ratings is that the higher the number the better the protection. This classification system can be misleading, not only because appropriate IP ratings are dependent upon the enclosure’s application, but also because the two digits indicate separate criteria.
The first digit in the rating is indicative of the enclosures protection against the ingress of solids whereas the second digit classifies the extent to which the enclosure is protected against liquids. In common practice when an enclosure is not rated, or rating has been omitted due to irrelevance, numbers are replaced by the character “X”.
For more information about IP numerical values and their significance please visit the IP Ratings page in our technical section.
For light emitting diodes, the temperature of the light-emitting portion of the device (see PN junction), which is inversely correlated with its light output.
Colour temperature is measured in degrees Kelvin, which indicate hue of a specific type of light source. Higher temperatures indicate whiter; “cooler” colours, while lower temperatures indicate more yellow, “warmer” colours.
1,000 Hertz (cycles per second)
The new recommendation builds on the L and B ratings that originated with Philips Lumileds. First lumen maintenance was defined with a figure such as L70 at 50,000 hours implying that an SSL product would decline to 70% of its initial light output after 50,000 hours of usage – essentially reaching the end of its useful life. The B figure was added such that L70/B50 at 50,000 hours implies that 50% of a population of lights reach the L70 point in 50,000 hours.
L70 is a term used to specify a lumen maintenance factor for a light source. Lumen maintenance compares the amount of light emitted by a source when it is new with the amount emitted at a specific time in the future. The L70 figure is the time taken for the light emitted by the source to drop to 70 per cent of its ‘as new’ value. For example, if a luminaire produced 1,000 lm when new and produced 700 lumens after 30,000 hours it would have a L70 lumen maintenance of 30,000 hours.
70 percent is not the only measure used in the lighting industry – some use L50 or L80 to specify lumen maintenance factor.
The ratio of the light output of a lamp (lumens) to its active power (watts), expressed as lumens per watt (Lm/W).
Rapid visible light change occuring in fluorescent light systems.
The median life span of a very large number of lamps (also known as the average rated life). Half of the lamps in a sample are likely to fail before the rated lamp life, and half are likely to survive beyond the rated lamp life. For discharge light sources, such as fluorescent and HID lamps, lamp life depends on the number of starts and the duration of the operating cycle each time the lamp is started.
Lamp Material or Coating
The type of glass (or quartz) used in the glass envelope surrounding the light source. The material can also have coatings applied to achieve particular performances.
Lamp Rated Life
The number of operating hours at which half of a large group of product samples are expected to fail. The rated life is a median value of life expectancy; individual lamp life may vary considerably from the published rated life and operating conditions (e.g., temperature, hours per start) may affect actual life because rated life is based on standard test conditions. In addition, the way a product fails can vary by technology. For example, incandescent lamps abruptly stop producing any light while LEDs are considered to have failed when their light output drops below a certain fraction of the initial level.
Leading Edge Dimmer
A dimming device that regulates power to light sources by delaying the leading edge of each half cycle of AC power. Often used in conjunction with LED light sources.
Please see "Light Emitting Diode" entry.
An electrical component that converts input power to constant current. A driver keeps current consistent despite fluctuations in voltage, in turn, protecting an LED from voltage fluctuations and spikes.
A transparent or translucent element, which controls the distribution of light by redirecting individual rays. Luminaires often have lenses in addition to reflectors.
LIFETIME 10% FAILURE
Lifetime in hours, defined by reaching 10% failures (i.e. 90% survivors) for a population.
Light Emitting Diode (LED)
A solid state semi-conductor that converts electrical energy into light energy. Fundamentally, the diode consists of two regions, one holding a positive electrical charge, the other holding a negative electrical charge. When Voltage is introduced and current flows, electrons travel from the negative region to the positive (the P-N junction). Electrons moving across this junction release energy which in turn produces photons with visible wavelengths.
Output of luminous flux (lm).
Light that is directed to areas where it is not needed, and thereby interferes with some visual act. Light pollution directed or reflected into the sky creates a “dome” of wasted light and makes it difficult to see stars above cities.
Stands for Light Output Ratio - the percentage of light produced by a light source that makes it out of the enclosure. An LOR of 80 implies 20% of light produced was lost within the confides of the enclosure.
A fixed shield, usually divided into small cells that is attached to the face of a luminaire to reduce direct glare.
The decrease in lumen output that occurs as a lamp is operated, until failure. Also referred to as lamp lumen depreciation (LLD).
A unit measurement of the rate at which a lamp produces light. A lamp’s light output rating expresses the total amount of light emitted in all directions per unit time. Ratings of initial light output provided by manufacturers express the total light output after 100 hours of operation.
The ability of a lamp to retain its light output over time. Greater lumen maintenance means a lamp will remain brighter longer. The opposite of lumen maintenance is lumen depreciation, which represents the reduction of lumen output over time.
LUMEN MAINTENANCE @ 50,000 HRS
% of original lumen flux remaining after indicated (life-) time for a defined population, e.g. B50/L70 indicates 50% of the population retaining 70% of the original light output.
A measure of the luminous flux or quantity of light emitted by a source.
A complete lighting unit consisting of a lamp (or lamps), ballast (or ballasts) as required together with the parts designed to distribute the light, position and protect the lamps and connect them to the power supply. A luminaire is often referred to as a fixture.
The ratio, expressed as a percentage, of the light output of a luminaire to the light output of the luminaire’s lamp(s). Luminaire efficiency accounts for the optical and thermal effects that occur within the luminaire under standard test conditions.
The photometric quantity most closely associated with the perception of brightness, measured in units of luminous intensity (candelas) per unit area (square feet or square metre).
Luminance contrast quantifies the relative brightness of an object against its background. It can range from zero and one. The closer the luminance contrast is to one, the greater the relative brightness of the object against its background.
A term which expresses the visual sensation associated with the amount of light emitted from a given area. It is the subjective correlate of luminance. Colloquially, the term 'brightness' is used in this sense.
The ratio of the luminous flux emitted by a light source to the power consumed by it.
Luminous radiant power, measured in lumens. The overall light output of a lamp or luminaire.
the quantity which describes the power of a source or illuminated surface to emit light in a given direction. It is the luminous flux emitted in a very narrow cone containing the given direction divided by the solid angle of the cone. Expressed in candelas, or lumens per steradian.
A measure of illuminance in lumens per square metre. One lux equals 0.093 footcandle.
Researcher David L. MacAdam showed that a just noticeable difference (JD) in the colours of two lights placed side-by-side was about three times the standard deviation associated with making colour matches between a reference light and a test light) MacAdam 1942, Wyszecki and Stiles 1982). These JNDs form an elliptical pattern of “constant discriminability” in a chromaticity space, centred on the chromaticity of a reference light, known as MacAdam ellipse. For more information about MacAdam Elipses and colour tolerances see our colour tolerances article.
A luminaire installed for emergency-lighting purposes which is normally operated by the mains supply, the internal battery only taking-over when mains-failure is detected.
The materials used by an LED to obtain certain colours or hues. Examples being InGaN (Indium, Galium, Nitride), and AlInGaP (Aluminium, Indium, Galium, Phosphorous).
Maximum ambient temperature
The maximum ambient temperature for which a compact fluorescent lamp (CFL) product is warranted to achieve rated life.
A widely used material for printed circuit boards (PCBs) with a metal core (MC) for enhanced thermal performance.
A high-intensity discharge light source operating at a relatively high pressure (about 1 atmosphere) and temperature in which most of the light is produced by radiation from excited mercury vapour. Phosphor coatings on some lamp types add additional light and improve colour rendering.
Mercury vapour (MV) lamp
A high-intensity discharge lamp type that uses mercury as the primary light-producing element. Mercury vapour lamps produce light with a CCT from 3000 to 7000K.
Typically referring to night time outdoor lighting conditions, the region between PHOTOPIC and SCOTOPIC vision.
Metal halide (MH) lamp
A high-intensity discharge lamp type that uses mercury and several halide additives as light-producing elements. Metal halide lamps have better colour properties than other HID lamp types because the different additives produce more visible wavelengths, resulting in a more complete spectrum.
A type of connector commonly used on T-5 lamps. Similar in design to but smaller than medium bi-pin connectors, it uses two small pins that protrude from the lamp ends and are inserted into a fixture socket.
Minimum ambient temperature
The minimum temperature at which a compact fluorescent lamp (CFL) product is warranted to start.
Minimum dimmed level
The lowest dimmed level achieved by a ballast, expressed as a percentage of that ballast’s maximum light output.
Minimum load requirement
The minimum power required for an occupancy sensor to operate properly.
Minimum starting temperature
The minimum ambient temperature at which a ballast will reliably start fluorescent lamps.
Efficiency module; lumen output per Watt input (lm/VV).
Energy required to operate the module.
MODULE TEMPERATURE CONTROL
Protective feature with which the driver is regulating down the module power when a certain critical temperature of the module is passed.
For light, consisting of a single wavelength and having a very saturated colour.
Light with only one wavelength (i.e. colour) present.
Meaning 'single shell' in French, monocoque refers to a design technique whereby the outermost shell is the most structurally integral part of the construction, absorbing most of the stresses to which the body is subjected to.
The vertical distance between the luminaire and the working plane. Note that the floor is taken to be the working plane for any emergency lighting.
MUNSELL COLOUR SYSTEM
The Munsell Colour System defines colour in terms of Hue, Value and Chroma. Hue is defined as the actual colour, red, blue, green, etc. Value is defined as how light or dark a colour is. Chroma is defined as how strong or weak a colour is.
A unit of wavelength equal to one billionth of a metre.
A luminaire installed for emergency-lighting purposes which is operated only on detection of mains failure and is only normally switched through a key switch.
All permanently installed artificial lighting operating from the normal electrical supply that in the absence of adequate daylight is intended for use during the whole time that the premises be occupied.
(Negative temperature coefficient) - NTC thermistors are used to monitor the temperature of the LEDs and cut out when excessive temperature is detected. This system provides intelligent over temperature protection.
Please see "Organic Light Emitting Diode" entry.
Open area (anti-panic)
Areas of undefined escape routes in halls or premises larger than 60m2 floor area or smaller areas if there is any additional hazard such as use by a large number of people.
The frequency with which lamps are cycled on and off.
Operating electrode voltage
The voltage that ballast supplies to a lamps electrodes.
Operating Position or Burn Position
Mercury and High Pressure Sodium lamps may be operated in any burn position and will still maintain their rated performance specifications. Metal Halide and Low Pressure Sodium lamps, however, are optimized for performance in specific burn positions, or may be restricted to certain burn positions for safety reasons.
For electrical discharge lamps, this is the voltage measured across the discharge when the lamp is operating. It is governed by the contents of the chamber and is somewhat independent of the ballast and other external factors.
Organic Light Emitting Diodes
These are composed of carbon based organic materials. Contrary to regular LEDs, which are single point sources, OLEDs are made in sheets that act as a diffuse area of light. A technology still in its infancy, OLEDs current applications tend to centre around small displays, such as mobile phone screens. This technology still has far to come before it an be considered a viable option for general lighting.
A constituent part of the P-N semiconductor, the 'P' type material is made of a substance missing an electron from the outer ring of it's atomic structure, thus making it positively charged.
Ballast circuit in which the lamps connected to one ballast will operate independently of one another — if one lamp fails, the rest will stay on.
Cooling without power consumption.
A suspension device between a mount and a luminaire.
An inorganic chemical compound processed into a powder and deposited on the inner glass surface of fluorescent tubes and some mercury and metal-halide lamp bulbs. Phosphors are designed to absorb short wavelength ultraviolet radiation and to transform and emit it as visible light.
Materials used in a light source to produce or modify its spectral emission distribution. In fluorescent and high intensity discharge lamps, the phosphors fluoresce (emit visible light) when excited by ultraviolet radiation produced by mercury vapour inside the lamp when energised by an electric arc. In a light emitting diode, phosphors convert short-wavelength light or ultraviolet radiation produced by a semiconductor die into longer-wavelength light, usually with the goal of producing white illumination.
The measurement of light and related quantities.
Ability to see in well-lit conditions. Acuity generally better than under Scotopic vision.
A device used to integrate an electric lighting system with a daylighting system so lights operate only when daylighting is insufficient.
Plankian Black Body Locus
The line on a CIE Chromacity diagram that shows the colour temperature of an object when heated at temperature between 1000K and 10,000K. For more information see our correlated colour temperature article in our technical section.
For light emitting diodes, the portion of the device where positive and negative charges combine to produce light.
Light whose vibrations are oriented in (or around, for partially polarized light) a specific plane.
Power factor (PF)
The ratio of active power (in watts) to apparent power (in rms volt-amperes), power factor is a measure of how effectively an electric load converts power into useful work. Power factor (PF) is calculated using the equation PF = (active power) / [(rms voltage) x (rms current)]. Phase displacement and current distortion both reduce power factor. A power factor of 0.9 or greater indicates a high power factor ballast.
A method of starting fluorescent lamps in which the electrodes are heated before a switch opens to allow a starting voltage to be applied across the lamp. With preheat starting, the lamp flashes on and off for a few seconds before staying lit because several starting attempts may be necessary to establish the electric arc across the lamp electrodes. Often, the luminaire’s start button must be held down until the lamp lights. Preheat ballasts are less energy efficient than rapid-start or instant-start ballasts.
A fluorescent lamp in which the filament must be heated by use of a starter before the arc is created. These lamps are typically operated with electromagnetic ballasts.
Also referred to as preheat time and lamp preheat time. The length of time that a ballast heats a lamps electrodes before initiating the lamp arc. Rapid start ballasts preheat a lamp before initiating the arc in order to ease starting.
The luminaires come on automatically when somebody enters the room, once the room is vacant the luminaires are dimmed then turn off after a pre-determined time. Presence detection is often used in open-plan offices, storage rooms, corridors and stairwells.
Any one of three lights in terms of which a colour is specified by giving the amount of each required to match it by additive combination.
An optical component of a luminaire that is used to distribute the emitted light. It is usually a sheet of plastic with a pattern of pyramid-shaped refracting prisms on one side. Most ceiling-mounted luminaires in commercial buildings use prismatic lenses.
Refers to a type of rapid start ballast that optimizes the starting process by waiting until the lamp’s electrodes have been heated to apply the starting voltage, thus easing the load to the electrode and extending lamp life. Standard rapid start ballasts heat the electrodes during the starting process to allow quicker starting without flicker.
An HID ballast with a high voltage ignitor to start the lamp.
Pulse-width modulation (PWM)
Operating a light source by very rapidly (faster than can be detected visually) switching it on and off to achieve intermediate values of average light output; the frequency and the duty cycle (percentage of time the source is switched on) are important parameters in the modulation.
The calculations that measure and quantify the characteristic of light use algebraic formula. When measuring the colour differentiation from natural light we refer to a light sources colour rendering index, this value is typically denoted algebraically as "Ra". Hence why a "Ra" value is often listed amongst a lamps technical information. For more information about colour rendering see our "colour rendering index" entry.
The radiant flux emitted by a surface per unit area, measured in units of watts per meter squared (W/m2).
The total amount of energy emitted across all wavelengths, measured in Watts (W).
A method of starting fluorescent lamps in which the electrodes are heated prior to starting, using a starter that is an integral part of the ballast. Heating the electrodes before starting the lamps reduces the voltage required to strike the electric arc between the electrodes. A rapid-start system starts smoothly, without flashing.
Rated average lamp life
Also referred to as lamp rated life. Lamps are tested in controlled settings and the point at which 50% of a given sample burns out is listed as the lamps’ rated average lamp life.
Rated lamp life
The number of hours at which half of a group of product samples fail. The rated life is a median value of life expectancy; any lamp or group of lamps may vary from the published rated life. Rated life is based on standard test conditions.
Also referred to as rated light output from lamp in lumens. Lumen refers to a unit measurement of the rate at which a lamp produces light. A lamp’s light output rating expresses the total amount of light emitted in all directions per unit time. Manufacturers rate their lamps’ initial light output after 100 hours of operation.
The time necessary for the batteries to regain sufficient capacity to achieve their rated duration.
A measure of the ability of an object to reflect or absorb light, expressed as a unitless value between 0 and 1. A perfectly dark object has a reflectance of 0, and a perfectly white object has a reflectance of 1.
A light source with a built-in reflecting surface. Sometimes, the term is used to refer specifically to blown bulbs like the R and ER lamps; at other times, it includes all reflectorised lamps like PAR and MR.
Portion of water vapor in a mixture of air and watervapor (%).
The time required for a lamp to restrike, or start, and to return to 90% of its initial light output after the lamp is extinguished. Normally, HID lamps need to cool before they can be restarted.
RGB Colour Model
An additive colour model wherein red, green and blue light are combined in different proportions to produce a broad range of colours, including white.
One way to produce white light by combining red, green and blue LEDs, though this approach produces a poorer quality of the white light.
Room Index (k)
An index related to the dimensions of a room and used when calculating the utilisation factor and other characteristics of the lighting installation.
Vision where the rods of the retina are exclusively responsible for seeing, typically like the light levels in the countryside on a moonless, starlit night.
Scotopic / Photopic (S/P) Ratio
This measurement accounts for the fact that of the two light sensors in the retina, rods are more sensitive to blue light (scotopic vision) and cones to yellow light (photopic vision). The scotopic / photopic (S/P) ratio is an attempt to capture the relative strengths of these two responses. S/P is calculated as the ratio of scotopic lumens to photopic lumens for the light source. Cooler sources (higher colour temperatures lamps) tend to have higher values of the S/P ratio compared to warm sources.
A discharge lamp with an integral ballasting device allowing the lamp to be directly connected to a socket providing line voltage.
Self-Test Emergency Lighting System
Self-contained emergency luminaires with in-built microprocessor which automatically initiates an emergency functional test every 8 days (2 minute test will be automatically performed to test the functionality of the lamp and battery). Every 2 months a full duration test is performed.
Self-Contained Emergency Luminaire
A luminaire or sign providing maintained or non-maintained emergency lighting in which all the elements such as the battery, the lamp and the control unit are contained within the housing or within one metre of the housing.
Ballast circuit in which the lamps connected to one ballast will operate both as a group and independently - if one lamps in the series connected section fails, the rest of the lamps in that section will also turn off but the lamps in the parallel circuit will remain on.
The mean illuminance throughout the life of an installation and averaged over the relevant area; the area may be the whole area of the working plane in an interior, or the area of the visual task in its immediate surroundings.
Blocking an electric or magnetic field with a metallic substance. The incident field induces currents in the metallic substance, and these currents induce a field that opposes the incident field. Shielding reduces radiated electromagnetic waves. Electronic components, wires, lamps, and devices can all be shielded.
These units of measurement were agreed upon at the 11th Conference for Weights and Measures in 1960. It was decided that to standardise communication of weights and measures in Europe a single system would be adopted. The adopted system was to be named the International System of Units, or Système International d'Unités in French, hence 'SI'. The SI system outline 7 base quantities and 7 base units; Length - metres (m), Mass - kilograms (Kg), Time - seconds, Electric current - Amperes (A), Thermodynamic temperature - Kelvin (K), Volume - moles (mol), Luminous intensity - candelas (cd). Algebraic logic can be applied to these base units to produce coherent derived units i.e. Acceleration = m / s².
A mathematical function used to represent AC voltage and current.
Brightening of the sky caused by outdoor lighting and natural atmospheric and celestial factors.
Lighting fixtures that are enabled for connectivity becoming a node in the network by containing one or more sensors and having the ability to change behaviour as a response to a stimulus.
Surface mount device, an acronym typically used describe the manner in which LED's are mounted. i.e. SMD LED
A term used to describe lighting solutions with no moving parts or parts that are liable to break, shatter, rupture or contaminate the environment.
Spectral Luminous Efficiency Function
A bell shaped curve detailing the sensitivity a human eye to visible light. Sometimes referred to as the eye sensitivity curve.
The reflected angle of light striking a surface, which is equal to and in the same plane as the incident angle.
Specular lighting is the effect whereby light reflecting off of a smooth surface results in a shiny spot on the object, this is called a specular highlight. A typical example might be on snooker ball. The reflecting specular highlight is normally the same colour as the light source it is subject to, though it can sometimes take on colour components from the object. Specular lighting is of great importance in computer graphics as it allows the brain to infer 3D shape to a 2D visual.
Light incident on a surface that is redirected at the specular angle. Glossy or shiny surfaces exhibit a high degree of specular reflection.
A colloquial term referring to a reflector lamp with a tight beam of light, typically around 10 degrees or less. It comes from the fact that such a lamp produces a narrow spot of light as opposed to a wide flood of light.
Standard Service Illuminance
The service illuminance recommended for standard conditions; subject to modification in certain circumstances. See "Service Illuminance" for more information.
Lighting which enables work to continue in the case of failure of the normal lighting system.
Device for starting a discharge lamp (in particular a fluorescent lamp) that provides for the necessary preheating of the electrodes and / or causes a voltage surge in combination with the series ballast.
Starting Temperature (Minimum)
The minimum ambient temperature at which the lamp will start reliably.
The time it takes the lamp to start from the point at which voltage is applied to the lamp until stable operation.
A unit of measure equal to the solid angle subtended at the centre of a sphere by an area on the surface of the sphere equal to the square of the sphere radius.
Switch-start fluorescent lamp
Fluorescent lamp suitable for operation with a circuit requiring a starter for the preheating of the electrodes.
Efficiency module + driver (lm/W).
Energy required to operate the system.
T-12, T-8, T-5
A designation for the diameter of a tubular bulb in eighths of an inch; T-12 is 12 eighths of an inch, or 11/2 inches, T-8 is 1 inch, T-5 is 5 eighths of an inch, and so on.
Supplemental lighting provided to assist in performing a localized task, e.g. a table lamp for reading or an inspection lamp for fabric inspection
TC LIFE DRIVER
Temperature of indicated point on the product on which the lifetime is based (°C).
TC LIFE MODULE
Temperature of indicated point on the product on which the lifetime is based (°C).
A self resetting switch that disconnects power to the ballast if internal temperatures rise above the trip point - typically 105°C. Thermal protector are used in some ballasts to limit maximum case temperature and meet UL Class P safety standards.
Third multiple of the fundamental frequency that will add in the third wire of a three-phase, 4 wire system and could cause overheating of the neutral wire.
Current delivered through three wires of a transformer with each wire serving as the return for the other two.
Time delay range
For motion sensors, the range of time that may be set for the interval between the last detected motion and the turning off of the lamps.
A new way to measure colour rendering that is set to replace the traditional CRI metric in the US. TM-30-15 relies on separate fidelity and gamut metrics, as well as a set of colour samples that is more representative of real-world objects as opposed to the pastel samples that were primarily used for the baseline CRI metric. The new color metric is intended to fairly and accurately characterise both LED-based solid-state lighting (SSL) and legacy sources.
Total Harmonic Distortion (THD)
The combined effect of harmonic distortion on the AC waveform produced by the ballast or other electrical devices.
Transformers are electrical devices with no moving parts, which change distribution voltages to higher or lower levels. When used with incandescent or halogen lamps, they typically step 120-V distribution downward to 12V, although 5.5V and 24-V models are also offered.
Transients are sudden but significant deviations from normal voltage levels - voltage spikes.
Control of light source intensity at three discrete levels in addition to off.
Tri-phosphors are a blend of three narrow-band phosphors (red, blue, and green) that provide improved colour rendition and higher light output versus some other types of phosphors.
A decorative luminaire accessory.
Any radiant energy within the wavelength range 100 to 400 nanometers is considered ultraviolet radiation (1 nanometer = 1 billionth of a meter, or 1 X 10-9 m).
The degree of variation of illuminance over a given plane. Greater uniformity means less variation of illuminance. The uniformity ratio of illuminance is a measure of that variation expressed as either the ratio of the minimum to the maximum illuminance or the ratio of the minimum to the average illuminance.
Light directed upward at greater than 90° above nadir. The source of uplight can be from a combination of direct uplight and reflected light.
Coefficient of utilization is the ratio of the luminous flux (lumens) received on a plane to the light output (lumens) of the lamps. Coefficient of utilization depends on luminaire efficiency, distribution of light from the luminaire, size and shape of the room, and reflectance’s of surfaces in the room. Specifiers use the coefficient of utilization to evaluate how effectively a luminaire delivers light to a work plane.
Lighting from light sources on a wall typically above eye level, shielded by horizontal panels. The light may be upward or downward directed
Viewing distances are given in EN 1838 as 200 X H for internally illuminated signs, and 100 X H for externally illuminated signs where H is the height of the pictogram.
The portion of the electromagnetic spectrum that is visible to the human eye (typically between 390nm and 750nm).
The full extent of what can be seen when looking in a given direction.
A measure of electrical potential, express in Volts (V).
Drop in Voltage levels of electrical distribution system, which interferes with the operation of electrical and electronic equipment. Also called "Brownout", results when demand for electricity exceeds capacity of the distribution system.
The time it takes for a lamp to produce 90% of its initial light output when it is started, unless otherwise indicated.
Refers to a colour temperature around 3000K, providing a yellowish-white light.
The distance between two corresponding points of a given wave. Wavelengths of light are measured in nanometers (1 nanometer = 1 billionth of a meter). The wavelength of light is between 390 and 750 nanometers.
The weight of a luminaire plus ballast (except for certain track luminaires with separately mounted ballasts, when the weight is that of the lamp and track head only). For modular compact fluorescent lamp (CFL) ballasts, the weight of the ballast without a lamp. For self-ballasted CFLs, “weight” indicates the total product weight.
Plane at which work is done and at which illumination is specified and measured; unless otherwise indicated, it is assumed to be a horizontal plane 30 inches above the floor (table-top height) having the same area as the floor.
Zhaga is an industry-wide cooperation between companies aimed at enabling the interchangeability of LED light sources made by different manufacturers.