Lighting Glossary

Lighting used to emphasize or draw attention to a special object or building. Accentuating light makes for a less formal atmosphere. The key to accent lighting lies in harnessing illuminance to create marked contrasts and hard-edged shadows, different brightness levels and angles of light incidence. It works only if its brighter than the general lighting.
Our eyes take time to adjust to changes in brightness. This process is called adaptation and is made possible by the eyes ability to change the size of the pupil to suit different luminance levels. How much adaptation is required and how long it takes depends on the levels of luminance before and after the brightness changes. Adapting to brighter conditions (light adaptation) takes only a matter of seconds; adapting to darkness (dark adaptation) is a much longer process. It takes the human eye around 30 minutes, for example, to adapt from indoor lighting to the darkness outdoors at night. The adaptation process impacts on visual performance.
Devices such as motion sensors, timers and dimmers used in concert with outdoor lighting equipment to vary the intensity or duration of operation of lighting.
Dynamic lighting that is dependent on lighting conditions during the course of the day is referred to as adaptive lighting. Its applications include lighting in rooms with no or little incident daylight as well as deep open-plan offices. The simulated daylight process can be governed by a time-based programmed or controlled by sensors monitoring one or more lighting variables.
The general overall level of lighting in an area.
A device used with a discharge lamp to obtain the necessary voltage, current, and/or wave form for starting and operating the lamp.
Bathroom luminaires are special luminaires for use in damp interiors. Operational reliability is assured by a degree of protection and protection class rating.
The luminaires are predominantly used for path-lighting. They radiate light from low mounting heights between 1 and 1.5 meters. Most bollard luminaires are fitted with optical control systems. The most widely used light sources are compact fluorescent lamps and halogen lamps, which are now joined by LEDs as an alternative.
The angle between the two directions in the plane in which the intensity is equal to a given percentage (usually 10 percent) of the maximum beam intensity.
The angular dimension of the cone of light from lamps encompassing the central part of the beam out to the angle where the intensity is 50% of maximum.
A measure of the accuracy with which a light source of a particular CCT renders different colors in comparison to a reference light source with CCT. A high CRI provides better illumination with the same or lower lighting levels. It is important not to mix lamps with different CCTs and CRIs. Specify both the CCT and CRI when purchasing lamps.
A measure in degrees Kelvin (°K) of light’s warmness or coolness. Lamps with a CCT of less than 3,200 °K are pinkish and considered warm. Lamps with a CCT greater than 4,000 °K are bluish–white and considered cool.
Luminaires are divided into different classes of protection according to their design and mode of operation. There are three protection classes, based on the measures taken to guard against electric shock: Class I: Luminaires for connection to the line-side PE conductor. The symbol is shown at the point of connection. Class II: Luminaires with additional or increased insulation. They have no PE conductor terminal. Class III: Luminaires operated on protective extra-low voltages
Cove luminaires are installed in the curving transition – the cove or coving – between wall and ceiling. A source of indirect lighting, they cast a diffuse light that brightens the edges of the ceiling. Cove luminaires are also available with housings which themselves form the coving.
A luminaire light distribution where the candela per 1000 lamp lumens does not numerically exceed 25 (2.5 percent) at or above an angle of 90° above nadir, and 100 (10 percent) at or above a vertical angle 80° above nadir. This applies to all lateral angles around the luminaire.
The reduction of luminous flux emitted by LEDs. The process is normally very slow and noticeable only with old LEDs after very many operating hours. Degradation is taken into account in the 50,000-hour rated life of LEDs: they emit light for longer but their luminosity beyond the 50,000 hour mark is noticeably reduced. The ageing process can be accelerated by adverse operating conditions – e.g. high ambient temperatures.
The process by which the eye becomes adapted to a luminance less than about 0.03 candela per square meter (0.01 footlambert).
Luminaires need to be designed to minimize the risk of penetration by solid foreign bodies and moisture. The degree of protection provided is indicated by an IP code ("Ingress Protection") made up of two numerals (see "Degrees of protection" table). The first numeral (1 to 6) indicates the degree of protection against solid foreign bodies, the second (1 to 8) the degree of waterproofness. Higher degrees of protection include those lower down the scale. Where one of the two numerals is missing, its place is taken by a capital "X", which means "untested".
A device used to distribute light from a source.
The glare that results in reduced visual performance and visibility. It often is accompanied by discomfort.
The glare that producing discomfort. It does not necessarily interfere with visual performance or visibility.
Direct lighting is where luminaires cast their light directly into the room onto surfaces or zones where light is needed. See also indirect lighting.
A mixture of direct and indirect lighting in a room is generally found agreeable. This can be provided by using luminaires designed solely for direct lighting in conjunction with models designed exclusively for indirect lighting. However, there are also many luminaires available which combine direct and indirect lighting in a single light fitting – for example pendant ceiling luminaires and free-standing luminaires. As a general rule, most of the light cast by these luminaires is indirect (cast onto ceiling or walls); direct lighting is provided by an additional light exit underneath.
Downlight has become an established term for ceiling luminaires of normally round design fitted with reflectors and/or other elements for optical control. Downlights can be fixed or swivel-mounted and are available in designs for recessed mounting in ceilings (recessed downlights) or for surface-mounting on ceilings (surface downlights). Downlights are also suitable for illuminating the interior of cabinets or showcases. Downlights are commonly designed for use with low-voltage halogen lamps, high-voltage halogen lamps, compact fluorescent lamps and metal halide lamps.
Lighting is described as "dynamic" when it changes during the course of time in one or more than one respect, e.g. in terms of illuminance, light color or direction of light (changes occurring either separately or simultaneously). Colored dynamic lighting generated by LEDs or fluorescent lamps for RGB color mixing is currently in vogue. Dynamism is monitored by appropriately programmed control systems.
The free and complete software developed by us for professional light planning is open to luminaires of all manufacturers. A software by planners for planners. Used by many hundred thousands of light planners and designers worldwide. And their number is growing from day to day.
The ratio of light output to its consumption of power, measured in lumens per watt (lm/W), or the ability of a lighting system to produce the desired result. Efficiency: A measure of the effective or useful output of a system compared to the input of the system.
ENEC is the European safety test mark for luminaires and other electrical products. It is awarded by independent test and certification institutes in Europe. In Germany this is VDE, which is identified by the testing agency number "10" beside the ENEC symbol. The acronym ENEC stands for European Norm Electrical Certification.
Safety signs for escape routes are available as back-lit signs – i.e. escape sign luminaires – or illuminated safety signs. Both need to conform to certain quality criteria set out in DIN EN 1838, notably in terms of color, luminance of the safety color green, luminance contrast and pictogram height.
The illumination of the exterior of a building
The assembly that holds the lamp in a lighting system. It includes the elements designed to give light output control, such as a reflector (mirror) or refractor (lens), the ballast, housing, and the attachment parts.
Floodlights are designed for lamps with high power (watt) ratings. Lamps with lower power ratings are used in spots or mini-floods. In exterior lighting, floodlights lend themselves to applications such as illuminating buildings; indoors, their principal application is theatrical stage lighting.
Illuminance produced on a surface one foot from a uniform point source of one candela.
The average luminance of a surface emitting or reflecting light at a rate of one lumen per square foot.
A luminaire light distribution where zero candela intensity occurs at or above an angle of 90° above nadir. Additionally the candela per 1000 lamp lumens does not numerically exceed 100 (10 percent) at or above a vertical angle of 80° above nadir. This applies to all lateral angles around the luminaire.
General lighting - also referred to as basic or background lighting - is the uniform lighting that gives us an overall picture of the room and enables us to get our bearings. It takes no special account of specific visual tasks performed at different points in the room. General lighting makes sure that architecture, objects and persons in the room are visible. Supplementary lighting can be used to illuminate individual areas (see also accent lighting, room-related lighting).
Intense and blinding light that reduces visibility. A light within the field of vision that is brighter than the brightness to which the eyes are adapted. Glare can seriously impair visibility: it reduces visual performance (disability glare) and visual comfort (discomfort glare). A distinction needs to be made between direct and reflected glare: direct glare is caused by luminaires or other surfaces with excessively high luminance, e.g. windows. Reflected glare is caused indirectly by light reflecting from shiny surfaces. Glare is limited by shielding the source of glare and using less reflective materials.
In a discharge lamp, the emitted energy (light) is produced by the passage of an electric current through a gas. High-intensity discharge (HID) include mercury, metal halide, and high pressure sodium lamps. Other discharge lamps are LPS and fluorescent. Some such lamps have internal coatings to convert some of the ultraviolet energy emitted by the gas discharge into visual output.
HID lamp where radiation is produced from sodium vapor at relatively high partial pressures (100 torr). HPS is essentially a “point source”.
A conventional lighting along streets and highways involve mounting heights of 15 meters (49.2 ft.) or less. Poles of 20 meters (65.6 ft.) or greater height have been utilized in a large parking lots, interchanges and complex intersections in both urban and rural areas and tangent sections with more than six lanes.
Density of luminous flux incident on a surface. Unit is footcandle or lux.
The professional society of lighting engineers, including those from manufacturing companies, and others professionally involved in lighting.
Light is produced by a filament heated to a high temperature by electric current.
Indirect lighting is where light from luminaires is directed exclusively onto a ceiling or walls and reflected back into the room. Lamps are screened from view and light emission above eye level prevents glare. Indirect lighting is generally used in combination with direct lighting. Used on its own, it can create a diffuse atmosphere with pale shadows. Where indirect lighting is used, ceiling and walls should be light-colored for high reflectance; in dark rooms, indirect lighting would require high-wattage lamps, which would result in high energy consumption.
Electromagnetic radiation with longer wavelengths than those of visible light, extending from the nominal red edge of the visible spectrum at 700 nanometers to 1 mm.
The degree or amount of energy or light.
A non-profit organization whose goals are to build awareness of the value of dark skies, and of the need for quality outdoor lighting.
Illuminance at a point varies directly with the intensity, I, of a point source and inversely as the square of the distance, d, to the source. E = I / d2
An electronics format of photometric data of an individual luminaire created according to the standard no. IES LM-63-02 - Standard File Format for Electronic Transfer of Photometric Data published by Illuminating Engineering Society of North America. This IES file is widely used by lighting professionals who use lighting design software as part of their lighting specification process.
A unit of energy equal to the work done by one kilowatt (1000 watts) of power acting for one hour.
Light emitting diode.
Any adverse effect of artificial light.
A measurement of a person’s comfort and perception based on the lighting.
Unwanted spillage of light onto adjacent areas and may affect sensitive receptors particularly residential properties and ecological sites.
Light falling where it is not wanted or needed. Spill light. Obtrusive light.
Devices used for either turning lights on and off or for dimming. Photocells Sensors that turn lights on and off in response to natural light levels. Some advanced mode can slowly dim or increase the lighting. See also: Adaptive Controls.
A discharge lamp where the light is produced by radiation from sodium vapor at a relatively low partial pressure (about 0.001 torr). LPS is a “tube source”. It is monochromatic light.
Unit of luminous flux; the flux emitted within a unit solid angle by a point source with a uniform luminous intensity of one candela.
The entire electric light fitting, including all the components needed to mount, operate and protect the lamp. Although also widely referred to as "lamps", luminaires actually perform a totally different function: they protect the lamp, distribute its light and prevent it causing glare.
The ratio of the light emitted by the luminaire compared to the light emitted by the enclosed lamps.
At a point and in a given direction, the luminous intensity in the given direction produced by an element of the surface surrounding the point divided by the area of the projection of the element on a plane perpendicular to the given direction. Units: candelas per unit area.
One lumen per square meter. Unit of illuminance.
A term to describe a luminaire light distribution widely used for outdoor luminaires.
Luminaires with a louvered enclosure, most of which are for use with tubular fluorescent lamps or compact fluorescent lamps, are referred to as louvered luminaires. Louvers provide optical control to shape intensity distribution and simultaneously guard against glare.
Maintenance factors form the basis of all lighting installation maintenance schedules. They depend on operating conditions as well as on the type of lamps, electrical equipment and luminaires used. Maintenance factors need to be defined and recorded by designers (and operators). Values required on installation are calculated as follows: value on installation = maintained value / maintenance factor. The lighting variable recommendations set out in European lighting standards such as DIN EN 12464-1, e.g. for levels of illuminance, refer to maintained values. These are values below which the lighting variables in question must never fall. However, because lamps, luminaires, walls and ceilings are subject to ageing and soiling, the values that are registered when lighting is new decline as operating time increases. So, to enable a lighting system to be operated longer without additional maintenance work, values on installation need to be correspondingly higher. How much higher is determined by maintenance factors.
An HID lamp where the light is produced by radiation from mercury vapor.
An HID lamp where the light is produced by radiation from metal-halide vapors.
The height of the fixture or lamp above the ground.
A point on the celestial sphere directly below the observer, diametrically opposite the zenith.
A luminaire light distribution where there is no candela limitation in the zone above maximum candela.
The components of a luminaire such as reflectors, refractors, protectors which make up the light emitting section.
A lighting control system that uses infrared beams to sense motion. When beams of infrared light are interrupted by movement, the sensor turns on the lighting system. If no movement is sensed after a predetermined period, the system turns the lights off.
PAR lamps – the abbreviation stands for Parabolic Aluminized Reflector – are pressed-glass reflector lamps available in three designs: as incandescent lamps, as high-voltage halogen lamps, both with E27 screw base, and as metal halide lamps with ceramic burner. They are available with various beam spreads and are used predominantly for outdoor illumination.
Pedestal luminaires – also known as pillar lights - are available for outdoor lighting. They are similar in appearance to post-top luminaires, and have similar lighting characteristics, but are mounted on walls or pillars instead of posts.
The quantitative measurement of light level and distribution.
A photoelectric lighting controller automatically switches one or more lights on and off when a pre-defined level of daylight (or artificial lighting) is reached. The brightness is monitored by an integrated light sensor. Its sensitivity should be infinitely adjustable, e.g. from two to 2,000 lux illuminance for outdoor lighting.
Power consumption is the electrical energy in Watts (W) consumed by a lamp (also referred to as lamp power or wattage) or a ballast. In the case of low-pressure and high-pressure discharge lamps, lamp power plus ballast power consumption is referred to as system power (consumption).
A transparent thermoplastic polymer featuring good optical and electrical properties, therefore largely used in lighting industry as an optical component.
A transparent thermoplastic polymer often used for outdoor luminaires. It has optical clarity, surface hardness, weatherablity and dimensional stability.
Recessed ceiling luminaires are for mounting in cavities or ceiling voids. Most of the luminaire is set into the ceiling out of sight, the luminaire face often flush with the ceiling. See also: surface-mounted ceiling luminaires, pendant luminaires.
An optic that achieves control of light by means of reflection (using mirrors).
An optic that achieves control of light by means of refraction (using lenses).
Recessed ground luminaires are generally floodlights that radiate light upwards. They are available with narrow- or wide-angled beams and symmetrical or asymmetrical intensity distribution curves. Recessed ground luminaires are mainly deployed outdoors but are also increasingly used for indoor lighting applications such as route-marking or providing accentuating light in hallways or bathrooms. Set into the ground or floor, they need to withstand the weight of pedestrians and wheeled vehicles and require a high degree of protection (IP 65 or IP 67). Optimized reflector technology boosts their light output ratio.
Reflector lamps have an integrated reflector (glass bulb with internal reflecting coating) which directs their light and determines beam spread. Reflectors are incorporated into normal incandescent lamps, PAR lamps and low- and high-voltage halogen lamps.
Diffuse, scattered sky light attributable to scattered light from sources on the ground.
A fixture designed to light only a small, well-defined area.
Semi-cylindrical illuminance (Ehz) is the amount of vertical illuminance in lux that falls on a semi-cylindrical surface. It is essential for identifying approaching figures. In outdoor car parks, for example, 1.5 – 5 lux (measured at a height of 1.5 metres above the ground) is correct.
Spots are luminaires used mainly for directional lighting. They are available for use with reflector lamps or in designs with reflectors incorporated into the luminaire. Spots are mounted on ceilings, walls, power track, wires or rods. They are often rotatable and swivel-mounted. Spots for exterior lighting require a higher degree of protection. They are also available in earth-spike designs.
These are luminaires for mounting directly on the ceiling. The luminaire housing is visible. Visible luminaire housings form part of room furnishings and thus double as an element of interior design. See also: recessed ceiling luminaires, pendant luminaires.
A luminaire light distribution where the candela per 1000 lamp lumens does not numerically exceed 50 (5 percent) at or above an angle of 90° above nadir, and 200 (20 percent) at or above a vertical angle 80° above nadir. This applies to all lateral angles around the luminaire.
Task area lighting caters for individual task areas and their immediate surroundings. According to DIN EN 12464-1 "Lighting of indoor work places", it is an alternative to room-related lighting. Task area lighting is particularly recommended where workplaces in a room have different visual and lighting requirements. For stationary task area lighting to be an option, the exact position of workplaces and task areas in the room needs to be known prior to installation. For more on this subject, see also work surface lighting and task area.
Task lighting is designed to supplement general lighting and cater to the special requirements of visual tasks performed at different points in the room. One example is bathroom mirror lighting, another is a reading light beside an armchair. In the world of work, light for special visual tasks is provided by workplace lighting and work surface lighting.
The task area is the part of the work place where the visual task is performed. The illuminance values set out in DIN EN 12464-1 apply to this area. Illuminance in the immediate surrounding area can be one grade lower.
A measure of signal distortion which assesses the energy that occurs on harmonics of the original signal. It is specified as a percentage of the signal amplitude.
A lighting control system using high–frequency sound waves pulsed through a space to detect movement by depth perception. When the frequency of the sound waves change, the sensor turns on the lighting system. After a predetermined time with no movement, the system turns the lights off.
Luminaires and floodlights for underwater use must meet special requirements to ensure safe and reliable operation: underwater floodlights and swimming pool luminaires for recessed or surface mounting are operated on protective extra-low voltages. Individual or collective upstream transformers are required. It is always advisable to have these special-purpose luminaires installed by a professional. Their installation and operation are governed by special safety regulations.
For the performance of a visual task, it is important to ensure not only the right lighting level but also the right degree of uniformity in the way the brightness is distributed. On some roads, the yardstick for this is uniformity of luminance; for all other applications, it is uniformity of illuminance.
Generally found as standard or wall luminaires, uplights direct most of their light upwards onto the ceiling to be reflected back into the room as indirect lighting. In uplights with a direct lighting component, the bottom of the reflector is translucent.
Electromagnetic radiation with wavelength shorter than that of visible light.
A luminance produced by bright sources in the field-of-view superimposed on the image in the eye reducing contrast and hence visibility.
Being perceived by the eye. Seeing effectively. The goal of night lighting.
Visual comfort describes the sense of wellbeing experienced by persons in the room as a result of lighting. It is the yardstick of lighting quality in terms of color rendering and harmonious brightness distribution. Lighting installations should offer visual comfort. However, they also need to meet all other quality requirements. For example, their light must not dazzle.
Visual performance is determined by the visual acuity of the eye and its sensitivity to differences in brightness and darkness. Time is another factor: visual performance is affected, for example, by the time it takes a motorist to make out differences in brightness, shapes, colors and details (speed of perception).
Visual tasks are defined by light/dark and color contrasts, by the size of details and by the speed at which contrasts need to be perceived. The harder the visual task, the higher the lighting level needs to be.
Unit of measure for electromotive force (EMF), the electrical potential between two points. An electrical potential of 1 volt will push 1 ampere of current through a 1-ohm resistive load.
Wall luminaires are used for task lighting, as a part of the general lighting system in a room and as a source of supplementary, accentuating light. They generally belong to a luminaire "family" of uniform design. Wall luminaires for exterior lighting may be mounted at the front door and around the building.
Working plane is the term used to denote the horizontal or vertical plane which artificial lighting is required to illuminate. Depending on the purpose of the lighting, standards stipulate a mathematical reference point - e.g. 0.75 m above floor-level - where illuminance should be assessed.
The unit for measuring power. In physics terms, one watt is one Joule of energy transferred or dissipated in one second. Electrical power is calculated as: Watts = Volts x Amps x Power Factor
The distance between two successive points of a periodic wave, in the direction of propagation, at which the oscillation has the same phase.
An imaginary point directly “above” a particular location, on the imaginary celestial sphere.
Ref. International Dark Sky Association
Illumination Engineering Society