General information, optic specifications, index

L952D953_SRC.QXD 11-03-2004 08:19 Pagina 12.14
Information – Lighting technique
However, the luminous intensity graph in the cartesian intensity
diagram gives a much better indication of the beam shape.The
luminous intensity in the cartesian diagram is given in absolute candela
values.Along the horizontal axis the -values of the C-plane are given,
while the vertical axis shows the absolute intensity values in candela.
Utilisation factor table
Room
Index
k
0.60
0.80
1.00
1.25
1.50
2.00
2.50
3.00
4.00
5.00
0.80
0.50
0.30
0.43
0.51
0.57
0.63
0.67
0.73
0.77
0.79
0.82
0.84
0.80
0.50
0.10
0.41
0.48
0.53
0.58
0.61
0.65
0.68
0.69
0.71
0.72
0.70
0.50
0.30
0.42
0.50
0.56
0.62
0.66
0.71
0.75
0.77
0.79
0.81
0.70
0.50
0.20
0.41
0.49
0.54
0.59
0.63
0.68
0.71
0.72
0.75
0.76
0.70
0.50
0.10
0.40
0.47
0.53
0.57
0.60
0.65
0.67
0.69
0.70
0.71
0.70
0.30
0.10
0.36
0.43
0.49
0.54
0.57
0.62
0.65
0.67
0.69
0.70
0.50
0.30
0.10
0.36
0.43
0.48
0.53
0.56
0.61
0.64
0.66
0.68
0.69
0.50
0.10
0.10
0.33
0.40
0.46
0.51
0.54
0.60
0.63
0.65
0.67
0.68
The Utilisation Factor table enables the lighting designer to
determine the number of luminaires required, or to calculate the
illuminance realised with a certain lighting installation.Although a lot
of calculation work has been taken over by computer, the Utilisation
Factor table is still a handy tool for lighting designers.The Utilisation
Factor (UF) of a lighting installation represents the percentage of the
luminous flux of the lamp(s) that reaches the defined working plane
in the room, which has to be seen as the efficiency of the lighting
installation.The Utilisation Factor depends on:
- light distribution of the luminaire
- luminaire efficiency
- reflection of ceiling, walls and floor/working plane of the room
- room index k
The room index k represents the geometrical ratio of the room, and
can be expressed as:
0.30
0.30
0.10
0.35
0.42
0.48
0.53
0.56
0.60
0.63
0.65
0.67
0.67
0.30
0.10
0.10
0.33
0.40
0.45
0.50
0.54
0.59
0.62
0.64
0.66
0.67
0.00
0.00
0.00
0.32
0.39
0.44
0.49
0.53
0.58
0.60
0.62
0.64
0.65
k =
L x W
Hwp ( L + W)
Where:
L = length of the room (m)
W = width of the room (m)
Hwp = height or vertical distance between the luminaires
and the working plane
Lumen method:
The UF can be looked up in the table for a range of values of the
room index k and a number of reflection value combinations.After
determining the UF for the specific layout for a luminaire, the
number of luminaires for a specific illumination level can be
calculated with the formula:
E x A
N =
x UF x MF
Alternatively, knowing the number of luminaires, the resulting
illuminance can be calculated with the formula:
x N x UF x MF
EAV =
Reflectances (%) for ceilings, walls and working plane
Recessed mounted
A
12.14 GENERAL INFORMATION, OPTIC SPECIFICATIONS, INDEX
Where:
N = required number of luminaires
EAV = specified average illuminance in lux
n = nominal lamp flux per luminaire (lumen)
UF = utilisation factor
MF = maintenance factor
A = surface area of the room (m 2
)
Quantity estimation diagram
Number of luminaires
hroom: 2.8 m
Reflectances: 0.70, 0.50, 0.20
60 Maintenance factor: 1.0
Recessed mounted
45
30
15
750 lx
500 lx
300 lx
0
20 60 100 140
2
180 (m )
The quantity estimation diagram gives a quick insight into the number of
luminaires that will be needed to reach the desired illuminance in a room.
The diagram gives the number of luminaires of one type needed for
different lighting levels, as a function of the area to be illuminated.Three
different diagrams exist.They are based on three fixtures' mounting
heights (2.8, 6 or 9 m, depending on the typical application,) and are made
for fixed reflection factors, as indicated in the diagram.The quantity
estimation diagram should only be used when the luminaires are placed
in a regular pattern, in, on or suspended from the ceiling. For calculation
purposes the space to be illuminated is considered to be rectangular.
The example shows that if 750 lux is required in an area of 100 m 2
,32
luminaires have to be installed.The information from this diagram should
be considered as a guideline. For exact figures, the lumen method or
computer calculations are required.The maintenance factor used for this
diagram is 1.0 but in practical situations a real maintenance factor has to
be taken into consideration.
Unified Glare Rating diagram (UGR)
hroom: 2.8 m
Reflectances: 0.70 0.500.20
Ceiling mounted
: viewed endwise
: viewed crosswise
: Parallel to viewing
direction
The Unified Glare Rating is an indication of the direct glare
perceived in a certain space illuminated by artificial lighting.
According to CEN (European Committee for Standardisation) the
Unified Glare Rating (UGR) should be determined according to the
CIE tabular method.