Modelling the impact of Modelling the impact of
urbanisation and weatherurbanisation and weather
on light pollution on light pollution
Afstand 5 km van stad 4x4 km 100.000 inwoners 1000 lum/inw
Henk Spoelstra
8th Dark Sky Symposium, Vienna, August 22-23, 2008
ContentsContents
► Intro & why modellingIntro & why modelling
►Light scattering in the atmosphereLight scattering in the atmosphere►How to modelHow to model►Effect of urbanisation & weatherEffect of urbanisation & weather
►Knowlegde gaps and future goalsKnowlegde gaps and future goals
Light scatteringLight scattering
in the in the atmosphereatmosphere
Light scatteringLight scattering
Air molecules Dust particles & Water droplets
Number ~ 7.1030 /cm3 Number ~ 103 - 105 /cm3
Dust particles & Water droplets scatter the light
~ factor 100 x MORE than air molecules
Diameter ~ 4.10-10 m (4 Å) Diameter ~10-8 – 2.10-5 m ~ 0,01 m – 20 m
Effect of light scatteringEffect of light scattering
Reflected indirect light: Intensity decreases
Direct light:Intensity increases
How to modelHow to model
PrinciplePrinciple
30 km
Modelling and first validationModelling and first validation
60 k
m
Apeldoorn
Ede
Modelling and first validationModelling and first validation
170000 180000 190000 200000
440000
450000
460000
470000
480000
490000
500000
Arnhem
Apeldoorn
Ede
Har
derw
ijk
Hattem
Nunspeet
Epe
170000 180000 190000 200000
440000
450000
460000
470000
480000
490000
500000
Arnhem
Apeldoorn
Ede
Har
derw
ijk
Hattem
Nunspeet
Epe
170000 180000 190000 200000
440000
450000
460000
470000
480000
490000
500000
Measured Calculated
EffectEffect
ofof
urbanisationurbanisation
Effect of urbanisationEffect of urbanisationInfluence of the size of a city
0.0001
0.001
0.01
0.1
1
10
1000 10000 100000 1000000
Number of citizens
Ze
nit
h s
ky
bri
gh
tne
ss
Co
ntr
ibu
tio
n
[mc
d/m
2]
Distance 4 km
Distance 18 km
Distance 10 km
Sky brightness increase ~ 0,7 x increase population
1200 lumen/cit x 4000 cit/km2 = 4,8 . 106 lum/km2
G =0.15 F=0.15
So…..So…..►Dust and water droplets very effective light Dust and water droplets very effective light
scatterers mainly in scatterers mainly in forwardforward direction direction
►Indirect light (from horizontal surfaces) Indirect light (from horizontal surfaces) causes mainly light pollution overheadcauses mainly light pollution overhead
►Direct light and indirect light from vertical Direct light and indirect light from vertical surfaces causes “long distance” light surfaces causes “long distance” light pollution pollution
And …..And …..►XX times bigger city -> times bigger city -> ~ ~ 0.7 X0.7 X times brighter sky times brighter sky (City roads, shopping malls, parking lots, business parks, …)(City roads, shopping malls, parking lots, business parks, …)
►YY times higher light flux -> times higher light flux -> YY times brighter sky times brighter sky (City Beautification, advertisement, …..)(City Beautification, advertisement, …..)
►ShieldingShielding ULR 30% -> 15% ULR 30% -> 15% Factor 4Factor 4 decrease of sky brightness decrease of sky brightness ULR 15% -> 0% ULR 15% -> 0% Factor 2Factor 2 decrease of sky brightness decrease of sky brightness
Thus …..Thus …..
►Shielding of fixtures is Shielding of fixtures is NECESSARYNECESSARY AND AND VERYVERY effective (up to factor ~ 7-8) effective (up to factor ~ 7-8)
►ButBut ALSO REDUCTIONALSO REDUCTION ofof::o the amount of illuminated surfacesthe amount of illuminated surfaceso the intensity of lightingthe intensity of lighting
EffectEffect
of of
weatherweather
Influence meteo : visibilityInfluence meteo : visibilityInfluence of meteo: visibility (dust)
0.001
0.01
0.1
1
10
1 10 100
Distance to edge of the city (km)
Co
ntr
ibu
tio
n t
o z
en
ith
sk
y b
rig
htn
es
s
mc
d/m
2
Aer 0,2,4,10.104, 4x4, 64000 inw
1200 lum/inw, 4000 inw/km2
F=0.15, G=0.15, no DS
> 40 km
2.6 km 6.5 km 12.5 km
CloudsCloudsKas 375 x 375 m, 6100 lux, afstand 1500m, zicht 10km, wolken 600m
So…..So…..
►Less visibility Less visibility = higher dust concentration (haze, = higher dust concentration (haze,
smog)smog) = more droplets (fog) = more droplets (fog)
►At larger distances : darkerAt larger distances : darker►At shorter distances : lighterAt shorter distances : lighter
Also in the case of cloudsAlso in the case of clouds
Knowledge gapsKnowledge gaps
andand
future goals future goals
UnknownUnknown
►How often occurs which light pollution How often occurs which light pollution level ? level ? (dependent on meteo)(dependent on meteo)
►What is the true amount of upward What is the true amount of upward light? light? (light sources in the local situation)(light sources in the local situation)
►What measures have to be taken, What measures have to be taken, where and how?where and how?
► Developing measures Developing measures
policypolicy
legislationlegislation
► Project !Project !
Future goalsFuture goals
Project 2008/2009Project 2008/2009
►One year continuous monitoring sky One year continuous monitoring sky brightness at 1 – 3 locations brightness at 1 – 3 locations
►Measuring & modelling effects of meteo Measuring & modelling effects of meteo and present measuresand present measures
►Results to be transformed into darkness Results to be transformed into darkness protection policyprotection policy
To see this again !To see this again !
Source:Kerry-Ann Lecky Hepburnwww.weatherandsky.com
Extra’s Extra’s
Distance relationshipDistance relationship
0.0001
0.001
0.01
0.1
1
10
1 10 100
Distance (km) from a city (size 8 x 8 km)
Co
ntr
ibu
tio
n t
o z
en
ith
bri
gh
tne
ss
[m
cd
/m²] 1/d1
1/d5
1/d2,5
(Walker)
Source: Dutch Platform LichthinderSource: Dutch Platform Lichthinder
Light output from Light output from fixturesfixtures
Direct and indirect upward Direct and indirect upward lightlight
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0 30 60 90
Degrees
Fra
cti
on
of
the
to
tal u
pw
ard
lig
ht
(F+
I)
F 0
Ground reflection 15%
Full-cut off15% reflec tion
100%15%I
Direct and indirect upward Direct and indirect upward lightlight
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0 30 60 90
Degrees
Fra
cti
on
of
the
to
tal u
pw
ard
lig
ht
(F +
I)
F 0
F 0.05
F 0.10
F 0.15
F 0.20
Ground reflection 15%
Full-cut off
15% reflec tion
F
I
20%
80%
12%
Shielding direct upward lightShielding direct upward lightInfluence direct upward light
0.00
0.05
0.10
0.15
0.20
0.25
0 10 20 30 40 50
Fraction direct upward light
Co
ntr
ibu
tio
n t
o z
en
it s
ky
bri
gh
tne
ss
mc
d/m
2
700 lumen
1400 lumen
4x410 km
Factor 2
30% -> 15% factor 4
15% -> 0% factor 2
30% -> 0% factor 8
