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Glossary of Lighting Terms

Average illuminance(Eave)
The arithmetic mean illuminance over the specified surface.

The SI unit of luminous intensity, equal to one lumen per steradian.

The Chartered Institution of Building Services Engineers.

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

Colour temperature
The temperature of a full radiator which emits radiation of the same chromaticity as the radiator being considered.

Correlated colour temperature

The temperature of a full radiator which emits radiation having a chromaticity nearest to that of the light source being considered, e.g., the colour of a full radiator at 3500K is the nearest match to that of a white tubular fluorescent lamp.
DALI (Digital Addressable Lighting Interface)
An industry standard digital interface system using a digital 8bit code to communicate dimming and operational instructions between luminaires.

Disability glare
Glare produced directly or by reflection that impairs the vision of objects without necessarily causing discomfort.

Discomfort glare

Glare which causes visual discomfort.

Diversity (DE)

The ratio of minimum to maximum illuminance over
a specified area.
Efficacy - See Luminous Efficacy

Electronic starters (ES)
Type of starter that replaces the usual canister glow starters found in fluorescent switch start circuits. Employs the use of electronics to create the conditions required to start the lamp. Most types also utilize a warm start feature that prolongs the life of the lamp cathodes.
Emission of electromagnetic radiation, especially light, by an object exposed to radiation or bombarding particles.

Full radiator
A thermal radiator obeying Planck's radiation law and having the maximum possible radiant exitance for all wavelengths for a given temperature; also called a 'black body' to emphasize its absorption of all incident radiation.
GLS (General Lighting Service)
Lamp type in which light is produced by an incandescent filament sealed within a glass envelope usually containing an inert gas filling, e.g. domestic light bulb.
HF (High frequency)
A type of fluorescent control gear that uses electronics to maintain the lamp discharge at 25 - 40kHz.
Kelvin (K)
The SI unit of temperature. Also unit of Colour temperature.
A construction of curved or angled pieces of material, usually aluminium, which is fixed below a luminaire to control the distribution of the light from the light source.

Lumen (lm)
The SI unit of luminous flux, used in describing a quantity of light emitted by a source or received by a surface. A small source which has a uniform luminous intensity of one candela emits a total of 4pi lumens in all directions.

Lumen depreciation
The progressive reduction in the output of a light source throughout its service life due to the action of internal pollutants.

An apparatus which controls the distribution of light given by a lamp or lamps and which includes all the components necessary for fixing and protecting the lamps and for connecting them to the supply circuit. Luminaire has officially superseded the term 'lighting fitting' which is still used colloquially.

Luminous efficacy (unit: lm/W)
The ratio of the luminous flux emitted by a lamp to the power consumed by the lamp.

Lux (lux)
The SI unit of illuminance, equal to one lumen per square metre (lm/m2)
A substance that can emit light when irradiated with particles of electromagnetic radiation. When coated on the inside of fluorescent tubes, these substances convert the ultra-violet light produced by the discharge into visible light.
An Induction lighting system constructed without lamp cathodes. Provides a quality of light comparable with HF tri-phosphor fluorescent but with a vastly improved lumen maintenance and life expectancy. See also Abbas range.
Radiant exitance (M unit:W/m2)
At a point on a surface, the product of the radiant flux leaving the surface.

Radiant flux (P, unit: W
The power emitted, transferred or received as radiation.
Uniformity (UE)
The ratio of the minimum illuminance to the average illuminance over a specified surface. The ratio usually applies to values on the task area over the working plane. (UE=Emin / Eave)
Note : Selected items within this page are taken from the CIBSE Code for interior lighting and reproduced by kind permission of CIBSE.
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