GLOSSARY

Illumination/ Lighting Incandescence
Emission of optical radiation by the process of thermal radiation.

Incandescent (electric) lamp
Lamp in which light is produced by means of an element heated to incandescence by the passage of an electric current.

Infrared radiation
Optical radiation for which the wavelengths are longer than those for visible radiation.

Intensity (I) / Luminous intensity (Iv, I)
Of a source in a given direction. Quotient of the luminous flux leaving the source, propagated in an element of solid angle containing the given direction, and the element of the solid angle containing the given direction, and the element of solid angle.
Unit candela, cd.

Intensity distribution / Luminous intensity distribution Distribution of the luminous intensities of a lamp or luminaire in all spatial directions.

Jet-proof luminaire
Luminaire constructed to withstand a direct jet of water from any direction.

Lamp mortality / Mortality rate.
The number of operating hours elapsed before a certain percentage of the lamps fail.

Lantern
see Luminaire

Light
Any radiation capable of causing a visual sensation direct i.e. Visible radiation

Light distribution
see Luminous intensity distribution

Light loss factor
see Maintenance factor

Light output ratio
Of a luminaire. The ratio of the total flux of the luminaire, measured under specified practical conditions, to the sum of the individual luminous fluxes of the lamps operating outside the luminaire under specified conditions.

Lighting (or illumination)
Application of light to a scene, objects or their surroundings so that they may be seen.

Louvre
Screen made of translucent or opaque components and geometrically disposed to prevent lamps from being directly visible over a given angle.

Low-pressure mercury (vapor) lamp
Mercury vapor lamp, with or without a coating of phosphor, in which during operation the partial pressure of the vapor does not exceed 100 Pa.

Low-pressure sodium (vapor) lamp
Sodium vapor lamp in which the partial pressure of the vapor during operation does not exceed 5 Pa - for example a SOX lamp.

Luminaire
Apparatus that distributes, filters or transforms the light given by a lamp or lamps and which includes all the items necessary for fixing and protecting these lamps and for connecting them to the supply circuit.
Note
In road lighting the term 'lantern' is also sometimes used.

Luminous efficacy (h)
Of a source. Quotient of the luminous flux emitted and the power consumed. Unit lumen per watt, lm/W.

Luminous flux (Fv), (F)
The quantity derived from radiant flux by evaluating the radiation according to its action upon the CIE standard photometric observer.
Unit lumen, lm.

Maintenance factor
Ratio of the average illuminance on the working plane after a specified period of use of a lighting installation to the average illuminance obtained under the same conditions for a new installation.
Note
The use of the term Depreciation factor as the reciprocal of maintenance factor is deprecated.

Metal halide lamp
Discharge lamp in which the major portion of the light is produced by the radiation from a mixture of a metallic vapor (for example, mercury) and the products of the dissociation of halides (for example, halides of thallium, indium or sodium). .

Metal vapor lamp
Discharge lamp such as the 'mercury (vapor) lamp' and the 'sodium (vapor) lamp' in which the light is mainly produced in a metallic vapor.

Mirror reflector
see Specular reflector

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