Apparent Colour
|
Of a light source, subjectivity the hue of the
source or of a white surface illuminated by the source; the degree of warmth
associated with the source colour. Lamps of low correlated colour temperature
are usually described as having a warm apparent colour, and lamps of high
correlated colour temperatures as having a cold apparent colour.
|
Aspect Factor
|
A function of the angle subtended at a point by
the length of a linear source, and of the axial distribution of luminous
intensity from the source; used in the calculation of luminance at a point.
|
BZ (British Zonal) System
|
A system for classifying luminaries as described
in CIBSE Technical Memorandum No.5. The BZ class number (e.g. BZ3) denotes
the classification of a luminaire in terms of the flux from a conventional
installation directly incident on the working plane, relative to the total flux
emitted below the horizontal (the direct ratio).
|
Candela (CD)
|
The SI unit of luminous intensity, equal to one
lumen per steradian.
|
Cavity index (CI)
|
A term, indicating the proportions of boundary
surfaces, used in determining the effective reflectance's of room surfaces
for interior lighting design: defined for cavity of length L, width W, and
depth d, as LW/(d (L+W)).
|
Chroma
|
In the Munsell system, and index of saturation of
colour ranging from 0 for natural Grey to 16 for strong colours. A low chroma
implies a pastel shade.
|
Chromatically
|
The colour quality of stimulus usually defined by
coordinates on a plane diagram in the colorimetric system (IE publication 15)
or by the combination of dominates wavelength and purity.
|
Colour Rendering Index (RI)
|
A measure of the degree to which the colours of
surfaces illuminated by a given light source conform to those of the same
surfaces under a reference illuminate, suitable allowance having been made
for the state of chromatic adaption. (CIE Publication 13.2)
|
Colour Temperature
|
The temperature of a full radiator, which emits
radiation of the same chromaticity as the radiator being considered.
|
Correlated Colour Temperature (Unit:K)
|
The temperature of a 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.
|
Daylight Factor
|
The luminance received at a point indoors, from a
sky of known or assumed luminance distribution, expressed as a percentage of
the horizontal luminance outdoors from an unobstructed hemisphere of the same
sky. Direct sunlight is excluded from both values of luminance.
|
Design Service Luminance
|
The service luminance in the lighting
specification. Design service luminance is derived from the standard service luminance
by taking account of the modifying factors in the flow chart.
|
Diffused Lighting
|
Lighting in which the luminous flux comes from
many directions, none of which predominates.
|
Direct Lighting
|
Lighting in which the greater part of the
luminous flux from the luminaries reaches the surface (usually the working
plane) directly, i.e. without reflection from surrounding surfaces. Luminaries
with a flux fraction ratio of less than 0.1 are usually regarded as direct.
|
Disability Glare
|
Glare which impairs the ability to see detail.
|
Discomfort Glare
|
Glare which causes visual discomfort.
|
Downward Light Output Ratio (DLOR)
|
The ratio of the total light output of a
luminaire below the horizontal under stated practical conditions to that of
the lamp or lamps under reference conditions.
|
Emergency Lighting
|
Lighting provided for use when the main lighting
installation fails.
|
Escape Lighting
|
Emergency lighting provided to ensure that the
means of escape can be safely and effectively used at all material times.
|
Flicker
|
A visible oscillation in luminous flux.
|
Flux Fraction
|
The proportion of luminous flux emitted from a
luminaire in the upper or lower hemisphere (upper and lower flux fraction).
|
Flux Fractions Ratio (FFR)
|
The ratio of the upward luminous flux to the
downward luminous flux from a luminate. It is also the ratio of the upper
flux fraction to the lower flux fraction and the ratio of the upward light
output ratio to the downward light output ratio.
|
General Lighting
|
Lighting designed to illuminate the whole area
uniformly, without provision for special local requirements.
|
General Surround Lighting
|
Lighting designed to illuminate the non-working
parts of a working interior.
|
Glare
|
The discomfort or impairment of vision
experienced when parts of the visual field are excessively bright in relation
to the general surroundings.
|
Hazardous Environment
|
An environment in which a risk of fire or
explosion exists.
|
Luminance (E)(Unit: Lm/m², LUX)
|
The illuminous flux density at a surface, i.e.
the luminous flux incident per unit area. (This quantity was formally known
as the illumination value or illumination level).
|
Initial Light Output (Unit:Lm)
|
The luminous flux from a lamp after 100 hours of
operation.
|
Installed Efficacy (Unit:Lm/W)
|
A factor, which quantifies the efficiency of a
lighting installation in converting electrical power to light. Specifically
it is the product of the lamp circuit luminous efficacy and the utilization
factor.
|
Isolux Diagram
|
A diagram showing contours of equal luminance.
|
Lamp Lumen Maintenance Factor (LLMF)
|
The proportion of the initial light output of the
lamp that is produced after a set time.
|
Light Loss Factor (LLF)
|
The ratio of the luminance provided by the
installation at some stated time, with respect to the initial luminance, i.e.
that after 100 hours of operation. The light loss factor is the product of
the lamp lumen maintenance factor, the luminaire maintenance factor and the
room surface maintenance factor.
|
Light Output Ratio (LOR)
|
The ratio of the total light output of a
luminaire under stated practical conditions to that of the lamp or lamps
under reference conditions. For the luminaire, the output is usually measured
in the designated operating position at 25°C ambient temperature with control
gear of the type usually supplied in a luminaire and operated at its normal
voltage. For the lamp the output is measured at 25°C ambient temperature and
with control gear of standard properties. This is a practical basis for
evaluating the total light output to be expected under service conditions.
|
Lighting Design Lumens (LDL) (Unit:Lm)
|
Lamps vary in flux output, both between
themselves and through their operating lives. The lighting design lumen is a
nominal value, which is representative of the average light output of each
type or size of lamp throughout its life.
|
Load Factor
|
The ratio of the energy actually consumed by a
lighting installation over a specified period of time to the energy that
would have been consumed had the lighting installation always been operating
during the period of time.
|
Local Lighting
|
Lighting designed to illuminate a particular
small area which usually does not exceed far beyond the visual task, e.g. a
desk light
|
Localized Lighting
|
Lighting designed to illuminate an interior and
at the same time to provide higher luminance over a particular part or parts
of the interior.
|
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
4 lumens in all directions and emits one lumen within solid angle (Steradian)
|
Luminaire
|
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 superseded the term light fitting.
|
Luminaire Maintenance Factor (LMF)
|
The lumen output from a luminaire declines with
time because of dirt deposition on and in the luminaire. The luminaire
maintenance factor quantifies this decline; being the proportion of the
initial light output from the luminaire that occurs after a set time,
allowance having been made for the decline in light output from the lamp.
|
Luminance (L)(Unit: Cd/m²)
|
The physical measure of the stimulus, which
produces the sensation of brightness measured by the luminous intensity of
the light, emitted or reflected in a given direction from a surface element,
divided by the area of the element in the same direction. The SI unit of
luminance is the candela per square metre; the relationship between luminance
and luminance is given by the equation.
|
Luminous Efficacy (Unit:Lm/W)
|
The ratio of the luminous flux emitted by a lamp
to the power consumed by the lamp. When the power consumed by control gear is
taken into account this term is sometimes known as lamp circuit luminous
efficacy and is expressed in lumens/circuit watt
|
Luminous Efficiency
|
The ratio of the radiant flux weighted according
to the CIE Standard Photometric Observer to the corresponding radiant flux.
|
Luminous Flux (Unit:Lm)
|
The light emitted by a source, or received by a
surface. The quantity is derived from radiant flux by evaluating the
radiation in accordance with the spectral sensitivity of the standard eye as
described by the CIE Standard Photometric Observer.
|
Luminous Intensity (Unit:Cd)
|
A quantity, which describes the power of a source
or illuminated surface to emit light in a given direction. It is the luminous
flux emitted in a very narrow cone containing the given direction divided by
the solid angle of the cone: the result is expressed in candelas.
|
Luminous Intensity
|
The distribution of the luminance provided by an
installation in the average condition of dirtiness expected in service, to
the luminance from the same installation when clean. The maintenance factor
is always less than unity, 1.
|
Mounting Height
|
Usually the vertical distances between a
luminaire and the working plane, but sometimes the distance between the
luminaire and the floor.
|
Operating Efficacy (Unit:Lm/W)
|
A term, which qualifies the efficacy of a
lighting installation in use. Specifically operating efficacy is the quotient
of the installed efficacy of the installation and the load factor.
|
Power Factor
|
In an electric circuit, the power factor is equal
to the ratio of the root mean square power in watts to the product of the
root mean square values of voltage and current; for sinusoidal waveforms the
power factor is also equal to the cosine of the angle phase difference
between voltages and current.
|
Room Index (RI)
|
An index related to the dimension of a room and
used when calculating the utilization factor and other characteristics of the
lighting installation:
|
|
Room Index =
|
LW
|
|
|
hm(L+W)
|
Where L is the length of the room, W the
width and hm the height of the luminaries above the working plane.
|
|
Room Surface Maintenance Factor (RSMF)
|
The proportion of the luminance provided by a
lighting installation in a room after a set time compared with that which
occurred when the room was clean, allowance having been made for the
deposition on luminaries.
|
Service luminance
|
The mean luminance throughout the maintenance
cycle of an installation, averaged over the relevant area. The area may be
the whole of the working plane or just the area of the visual task and its
immediate surround, depending on the lighting approach used.
|
Spacing to Height Ratio (SHR)
|
This ratio describes the distance between
luminaire centres in relation to their height above the working plane. For a
regular square arrangement of luminaries, it is the distance between adjacent
luminaries divided by their height above the working plane More generally,
spacing/height
ratio = (1/hm)Ö(A/N)
Where A is the total floor area, N is the number of luminaries
and hm is their height above the working plane.
|
Standard Service Luminance
|
The service luminance recommended for the assumed
standard conditions of the application, specified by the CIBSE guide.
|
Standby Lighting
|
Emergency lighting provided to enable normal
activities to continue.
|
Steradian (SR)
|
The unit of solid angle. A complete sphere
subtends 4 steradians from the centre.
|
Stroboscopic Effect
|
An illusion caused by oscillation in illuminous
flux, that amkes a moving object appears to be stationary or as moving in a
manner different from that which it is truly moving.
|
Upward Light Output Ratio (ULOR)
|
The ratio of the total light output of a
luminaire above the horizontal under stated practical conditions to that of
the lamp or lamps under reference conditions.
|
Utilization Factor (UF)
|
The proportion of the luminous flux emitted by
the lamps, which reaches the working plane.
|
Working Plane
|
The horizontal, vertical, or inclined plane in
which the visual task lies. If no information is available, the working plane
may be considered to be horizontal and 0.7m above the floor for offices,
horizontal and 0.85m above the floor for industry.
|
Emergency Lighting
Maintained
|
In this the lamp is on all the time. Under normal
conditions the mains power it directly or indirectly. Under emergency
conditions, one of the lamps normally operated by the mains, is energized
from it's own battery supply.
|
Emergency Lighting
Non-Maintained
|
In this the lamp is off when power is available
to charge the batteries. Upon supply failure the lamp is energized from the
battery pack.
|
Emergency Lighting
Sustained
|
This is a hybrid of the previous two. A lamp
provided which operates from the mains supply under normal conditions. Under
emergency conditions a second lamp, not normally energized under mains
operation, powered from the battery pack, takes over. Sustained luminaries
are often used for exit signs. Systems of self-contained luminaries are the
easiest and most flexible to install but their effective life is likely to be
less than that of central battery systems. Also, maintenance and testing must
be through if operation in the event of emergency is to be guaranteed.
|