Resources
Glossary of Lighting Terms
Ballast
Ballasts are electrical devices used with fluorescent or high intensity discharge (HID) lamps to supply sufficient voltage to start and operate the lamp but then to limit the current during operation. They can be either magnetic or electronic.
Batten and trunking systems
These are generally fitted with fluorescent lamps and are primarily used in commercial and industrial environments. Designed either as surface-mounted or pendant units, they are generally simple to install and can be used singly or as strip lighting. Suitable housings ensure that the light is directed as required and that glare is kept to a minimum.
Carbon dioxide (CO2)
An important greenhouse gas. Countries that ratified the Kyto agreement have committed to reduce their emissions. Lighting designers have the power to hold down CO2 emissions into the atmosphere (0.42 kg of carbon dioxide is produced for each 1kWh of electricity).
Colour Appearance
The colour emitted by a near-white light source can be indicated by its correlated colour temperature (CCT). Each lamp type has a specific correlated colour temperature measured in degrees Kelvin e.g. 3000K and are described as warm, intermediate, cool and cold.
Colour Rendering
The ability of a light source to reveal the colours of an object. It is determined by the spectral power distribution or spectrum of the light source. Measured by the colour rendering index (Ra). The higher the number the better, up to a maximum of 100.
Most artificial light sources other than incandescent lamps require special control gear to start the lamp and control the current after starting. Depending on the type of lamp involved, the control gear can take the form of ballasts, igniters or transformers.
Diffusers and moisture-proof fittings
Luminaires of a higher protection class. These are closed luminaires for humid, wet, chemically aggressive or dusty environments where the requirements for glare control are generally rudimentary.
Digital Serial Interface (DSI)
A lighting control protocol created by the Zumtoble Group, for applications where the addressing feature of DALI is not required.
Downlight
Ceiling luminaire that concentrates the light in a downward direction. Downlights are generally round or square and recessed into the ceiling, but may also be surface-mounted. They may feature an open reflector and/or a shielding device.
Columns
Poles for mounting roadlighting lanterns or floodlights. Also known as "masts" and "towers".
Contrast
Subjective experience of comparative brightness between points or areas of luminance, seen simultaneously or successively.
Contrast Rendering Factor (CRF)
A measure of the degradation of contrast that is caused by veiling reflections (bright reflections in the task).
Digital Addressable Lighting Interface (DALI)
A lighting control protocol set out in the technical standard IEC 929
Efficacy
Measured in lumens per Watt (lm/W) and a useful parameter for assessing how much light is available from the lamp for each Watt of power. Luminaire efficacy is often expressed by dividing the initial lamp lumens by the combined lamp and control gear power.
Emergency lighting
Lighting provided for use when the mains lighting fails for whatever reason.
Glare
Glare is the result of excessive contrasts of luminance in the field of view. The effect may vary from mild discomfort to an actual impairment of the ability to see. When the ability to see is impaired this is called disability glare. Discomfort glare is associated more with interiors; it refers to the discomfort or distraction caused by bright windows or luminaires.
High bay
As the term implies, these are for use when mounting heights of around 8-10m or above are encountered.
High frequency electronic control gear (HF)
Most artificial light sources other than incandescent lamps require special control gear to start the lamp and control the current after starting. HF electronic gear operates fluorescent tube(s) at high frequency (typically at 30-60 kHz) instead of the mains frequency of 50 Hz offering benefits of higher quality lighting, reduced running costs and ease of use, combined with safe reliable operation. Dimmable versions available. They may also be used with high intensity discharge lamps.
Igniter
Igniters are required for lamps that cannot be started using the normal line voltage alone. This is the case with high-pressure discharge lamps such as metal halide lamps and high-pressure sodium vapour lamps.
Illuminance
The amount of light falling on an area divided by that area - measured in lux. Generally, 500 lx is needed for office work, whereas a watchmaker requires 4,000 lux. In summer, the sun shines on the ground with 120,000 lux, and a full moon produces 3 lux.
Indirect Lighting
System of illumination where the light from lamps and luminaires is first reflected from a ceiling or wall.
Ingress protection (IP)
Denotes the protection against entry of dust/solid objects and moisture/water, provided by the luminaire enclosure.
Lamp
Lamps are artificial sources of light. There are many types, distinguished by the way they generate light, their light output or luminous flux, their power consumption, their luminous efficiency, their geometry,the spectral composition of the radiation emitted, their luminance and their beam characteristics.
LED / light-emitting diode
An LED or light-emitting diode is a small semiconductor device which emits light, usually coloured, when an electric current passes through it. LEDs are energy saving and have a long service life. LED light engines can generate any colour by mixing the individual spectral
Lighting control system
Lighting control systems are used to actively change the lighting situation. Such changes can take place automatically or as a result of intervention by a user. Lighting control systems often include operating equipment. Lighting can automatically respond to the level of daylight, it can be controlled by presence sensors to switch on or off depending whether people are in the room or can also progress through a sequence of changing scenarios.
Lighting Energy Numeric Indicator (LENI)
Defined in the European standard for assessing the Energy Performance of Buildings (EPBD), EN 15193 as the measure for the annual lighting energy requirement for the building per square metre.The quick method of calculation being:
LENI = W/A
W is the total annual energy used for lighting {kWh/year}
A is the total useful floor area of the building {m²}
Lighting management
Lighting management covers the entire concept of a controlled or regulated lighting system including emergency lighting and its use. As well as permitting efficient, user-focused operation of the lighting system, it also allows it to be monitored, thus facilitating maintenance.
Light Output Ratio (LOR)
The ratio of the total light output of the luminaire to the output of the lamp(s), under stated conditions.
Luminaires housing high intensity discharge lamps mounted horizontally at low heights 4-8m, typically in industrial, sporting and public concourses.
Lumen (lm)
The unit of luminous flux or the rate of flow of light from a source or received by a surface. When a ray of light hits a solid surface, the process is known as illumination.
Luminaire
Modern term for “light fitting” or “fixture”. A complete lighting unit that controls the distribution of light given by a lamp(s) and includes components for fixing and protecting the lamp(s) and for connecting them to the supply circuit. Luminaires for road lighting are often known as lanterns.
Luminaire-lumens per circuit watt
Is the luminaire efficiency factor given by LOR x (total bare lamp flux in the luminaire/circuit Watts).
Luminance
The measured brightness of a surface. The unit is cd/m².
Luminous intensity (candelas)
The amount of light that a small light source at the tip of a cone emits through a narrow cone in a given direction.
Lux
The unit of illuminance, equal to one lumen per square metre.
Modelling
The use of light to bring out the form of three-dimensional objects, structures or spaces.
The reflector and/or refractor system that directs the light emission from the lamp in the luminaire into required directions.
Spill Light
Stray light from a luminaire that incidentally illuminates nearby objects or surfaces within the public environment. Can be a cause of ‘light trespass’.
Spine
See batten
Track
A linear bus bar system providing one to three main circuits or a low voltage supply to which display lighting (spotlights) can be connected and disconnected at will along the length of the system.
Transformer
Transformers reduce the line voltage (for instance 230 V) to the lower voltage required for operating low-voltage halogen lamps. This will generally be 12 V.
Trunking
Trunking usually provides mechanical fixings for the luminaires as well as electrical connection.
Uniformity
The ratio of the minimum illuminance to the average illuminance over the specified area.
Visual performance
The ability to perceive detail and carry out the visual tasks.
Visual comfort
Our feeling of ease or well being within the visual field.
Visual satisfaction
The qualitative impression of a lit space.