Definition & Description of Terms

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1Basic Units and Symbols
The basic units and symbols used in this code are given in Table-2.1
SymbolDescriptionUnits
PPowerWatts
UTerminal r.m.s. VoltageV
ICurrentA
Luminous Fluxlm
EIlluminancelux
KLuminous efficacylm/W
LLength of spacem
WWidth of spacem
HHeight of fixture from the plane of measurementm
AAreamsq2
Table 2-1: Basic Units and Symbols
SymbolDescription
mMeasured value
RRated value
avAverage value
Table 2-2: Subscripts
2Description of terms
Circuit watts
Total power consumption of lamps plus ballasts in the lighting feeder/circuit
under consideration
Color Rendering Index (CRI)
is a measure of the effect of light on the perceived color of objects. A low CRI indicates that some colors may appear unnatural when illuminated by the lamp.
Installed Load Efficacy
This is the average maintained illuminance provided on a horizontal
working plane per circuit watt with general lighting of an interior expressed in lux/W/m²
Installed Load efficacy ratio
This is the ratio of Target Load efficacy and Installed load efficacy.
Lumen
Unit of luminous flux; the flux emitted within a unit solid angle by a point source with a uniform luminous intensity of one candela. One lux is one lumen per square meter.
Luminaire
A luminaire is a complete lighting unit, consisting of a lamp or lamps together with the parts designed to distribute the light, position and protect the lamps, and connect the lamps to the power supply
Lux
This is the metric unit of measure for illuminance of a surface. Average maintained illuminance is the average of lux levels measured at various points in a defined area. One lux is equal to one lumen per square meter.
Mounting height:
The height of the fixture or lamp above the working plane.
Rated luminous efficacy:
The ratio of rated lumen output of the lamp and the rated power
consumption expressed in lumens per watt.
Room Index
This is a ratio, which relates the plan dimensions of the whole room to the
height between the working plane and the plane of the fittings.
Target Load Efficacy:
The value of Installed load efficacy considered being achievable
under best efficiency, expressed in lux/W/m²
Utilisation factor (UF):
This is the proportion of the luminous flux emitted by the lamps,
which reaches the working plane. It is a measure of the effectiveness of the lighting scheme.

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