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Arc discharge (in a gas or vapor)
Electric discharge characterized by a cathode fall that is small
compared with that in a glow discharge.
Average illuminance (Eav)
Over a surface, Illuminance averaged over the specified surface.
Ballast
Device used with discharge lamps for stabilizing the current in
the discharge.
Beam axis
The direction in the center of the solid angle which is bounded
by directions having luminous intensities of 90% of the maximum
intensity of a luminaire.
Beam spread
The angle (in the plane through the beam axis) over which the luminous
intensity drops to a stated percentage of its peak intensity.
Cold-start lamp (instant-start lamp, USA)
Discharge lamp designed to start without preheating of the electrodes,
for example 'TL'S fluorescent lamp.
Color rendering
General expression for the effect of an illuminant on the color
appearance of objects in conscious or subconscious comparison with
their color appearance under a reference illuminant.
Color temperature
Temperature of the black body that emits radiation of the same
chromaticity as the radiation considered.
Unit Kelvin, K.
Dimmer
A device in the electrical circuit for varying the luminous flux
from lamps in a lighting installation.
Discharge lamp
Lamp in which the light is produced, directly or indirectly, by
an electric discharge through a gas, a metal vapor, or a mixture
of several gases and vapors.
Downlight (downlighter)
Small luminaire concentrating the light, usually recessed in the
ceiling.
Emergency lighting
Lighting provided for use when the supply to the normal lighting
fails. Flicker
Impression of fluctuating luminance or color.
Floodlight
Projector designed for floodlighting, usually capable of being
pointed in any direction and of weatherproof construction.
Fluorescent lamp
Discharge lamp of the low-pressure mercury type in which most of
the light is emitted by a layer of fluorescent material excited
by the ultraviolet radiation from the discharge.
Note
This term is most commonly applied to low pressure tubular
fluorescent lamps, for example 'TL', 'TL'D, 'TL'E lamps.
Fluorescent mercury lamp
A high-pressure mercury lamp in which the light is produced partly
by the mercury vapor and partly by a layer of fluorescent material
on the inner surface of the outer bulb excited by the ultraviolet
radiation of the discharge - for example: HPL-N, HPLR-N lamps.
Glare
Condition of vision in which there is discomfort or a reduction
in the ability to see significant objects, or both, due to an
unsuitable distribution or range of luminance or to extreme
contrasts in space
or time.
Halogen lamp
Gas-filled lamp containing a tungsten filament and a small proportion
of halogens. High-pressure mercury (vapor) lamp
Mercury vapor lamp, with or without a coating of phosphor, in which
during operation the partial pressure of the vapor is of the order
of 105 Pa - for example: HPL and HPL-N lamps.
High-pressure sodium (vapour) lamp
Sodium vapour lamp in which the partial pressure of the vapour
during operation is of the order of 104 Pa - for example, SON and
SON-T lamps.
Illuminance (E)
At a point on a surface. Quotient of the luminous flux incident
on an element of the surface containing the point, and the area
of that element.
Unit lux, lx.
Note
The orientation of the surface may be defined, e.g. horizontal,
vertical, hence horizontal illuminance, vertical illuminance.
Incandescent (electric) lamp
Lamp in which light is produced by means of an element heated
to incandescence by the passage of an electric current.
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 - for example a 'TL' lamp.
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.
Luminance (L)
In a given direction, at a given point of a real or imaginary surface.
Quotient of the luminous flux transmitted by an elementary beam
passing through the given point and propagating in the solid angle
containing the given direction, and the product of the solid angle,
the area of a section of that beam containing the given point,
and the angle between the normal to that section and the direction
of the beam.
Unit candela per square meter, cd/m2.
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) - for example: HPI-T lamps.
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.
Projector
Luminaire using reflection and/or refraction to increase the luminous
intensity within a limited solid angle.
Reflector lamp
Lamp in which part of the bulb is coated with a reflecting material,
either diffuse or specular, so as to control the light, for example:
HPL-R, MLR, and 'TL'F lamps.
Spotlight
A (small) projector giving concentrated light of usually not more
than 20° divergence.
Spread
Quantity of a luminaire to indicate the extent to which the light
is 'spread out'.
Luminaires are classified as being of narrow, average or broad
spread.
Starter
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.
Switch-start fluorescent lamp
Fluorescent lamp suitable for operation with a circuit requiring
a starter for the preheating of the electrodes, for example 'TL'D
type.
The Lightbulb Company (UK) Ltd acknowledges the
copyright of Philips Lighting B.V. as the source for this glossary.
© 2001 The
Lightbulb Company |
