Civil Engineering Reference
In-Depth Information
Fig. 16.6
Luminous flux
surf1
+
surf2
+
surf3
leaving the virtual surfaces
surrounding the area to be
lighted
ˆ
surf1
ˆ
surf2
ˆ
lum tot
ˆ
surf3
Fig. 16.7
Vertical
illuminance on inside vertical
surfaces of the virtual
enclosure of the area to be
lighted
E
vert virt
E
vert virt
“virtual vertical illuminance” at any point on the vertical inside surfaces of the same
virtual enclosure (Fig.
16.7
):
E
vert virt
Normally this parameter is used in combination with the parameter described in the
previous Section: total luminous flux leaving the virtual surfaces surrounding the
area to be lighted (and that is including the top surface).
16.2.2.4
BUG Luminaire Classification
IDA-IESNA uses the IES luminaire classification system, LCS, as described in
Sect. 11.1.2, to classify the light-pollution characteristics of a luminaire (IES
2007
).
This so-called BUG luminaire classification system divides the light distribution of
a luminaire
1
into three zones or solid angles (Fig.
16.8
):
•
the backward quarter sphere, denoted by the letter B, responsible for possible
light trespass (light beyond the area to be lit),
•
the upper hemisphere, denoted by the letter U, responsible for possible sky glow,
1
The light distribution of a luminaire here is given for the standard mounting position of the
luminaire. Adverse effects of tilting luminaires in an installation are therefore not taken into account
in the BUG system.
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