Civil Engineering Reference
In-Depth Information
Table 17.9
Maximum
allowable value of E
vert,virt
according to lighting zone.
(IDA-IES
2011
)
Lighting zone
E
vert,virt
(lx)
LZ0
0.5
LZ1
1
LZ2
3
LZ3
8
LZ4
15
illuminance,
surfvirt
and E
vertvirt
) have been described in Sect 16.2.2 (see Figs. 16.6
and 16.7). The total luminous flux leaving the vertical surfaces and the top surface
(
surfvirt
) should be less than 15 % of the total luminous flux of all luminaires,
lumtot
.
The maximum vertical illuminance at any point of the virtual vertical surfaces is given
in Table
17.9
.
17.5
Spectrum of Light
Light with shorter wavelengths (blue-greenish light) scatters more on the aerosol
particles of the sky and therefore increases sky glow relative to that produced by
yellowish-red light with its longer wavelengths. The spectral effect is different for
different animal and plant species. For example, blue-rich light has a relatively great
effect on sea turtles and insects, while blue and green light has little or no disturbing
effect on the migration course of birds. Many more studies are needed in order to
obtain a better insight in the influence of the spectrum on the different effects of light
pollution. It is probably for this reason that the CIE Guide on light pollution and the
IDA-IES MLO ordinance, dealt with in this chapter, do not give specifications for
the spectrum of light.
It is more than likely that different spectra will have to be recommended for
different locations with a different predominant disturbing effect. It also seems that
metrics such as correlated colour temperature and S/P ratio are not really suitable
enough for characterizing the effect of the spectrum on light pollution. In order
to give some guidance, the International Dark-sky Association IDA, in a separate
publication, suggests that the wavelengths of light sources employed in a wide area
around professional observatories, should be limited to greater than 500 nm in order
to restrict sky glow (IDA
2010
).
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