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Modelling the impact of urbanisation and weather on light pollution

Modelling the impact of urbanisation and weather on light pollution. Henk Spoelstra 8th Dark Sky Symposium, Vienna, August 22-23, 2008. Afstand 5 km van stad 4x4 km 100.000 inwoners 1000 lum/inw. Contents. Intro & why modelling Light scattering in the atmosphere How to model

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Modelling the impact of urbanisation and weather on light pollution

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  1. Modelling the impact of urbanisation and weather on light pollution Henk Spoelstra8th Dark Sky Symposium, Vienna, August 22-23, 2008 Afstand 5 km van stad 4x4 km 100.000 inwoners 1000 lum/inw

  2. Contents Intro & why modelling Light scattering in the atmosphere How to model Effect of urbanisation & weather Knowlegde gaps and future goals

  3. Light scattering in the atmosphere

  4. Light scattering Air molecules Dust particles & Water droplets Number ~ 7.1030 /cm3 Number ~ 103 - 105 /cm3 Diameter ~ 4.10-10 m (4 Å) Diameter ~10-8 – 2.10-5 m ~ 0,01 mm – 20 mm Dust particles & Water droplets scatter the light ~ factor 100 x MORE than air molecules

  5. Effect of light scattering Direct light: Intensityincreases Reflected indirect light: Intensity decreases

  6. How to model

  7. Principle

  8. Modelling and first validation Apeldoorn Ede 60 km 30 km

  9. Modelling and first validation Measured Calculated

  10. Effect of urbanisation

  11. Effect of urbanisation 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

  12. So….. Dust and water droplets very effective light scatterers mainly in forward direction Indirect light (from horizontal surfaces) causes mainly light pollution overhead Direct light and indirect light from vertical surfaces causes “long distance” light pollution

  13. And ….. X times bigger city -> ~ 0.7 X times brighter sky (City roads, shopping malls, parking lots, business parks, …) Y times higher light flux -> Y times brighter sky (City Beautification, advertisement, …..) Shielding ULR 30% -> 15% Factor 4 decrease of sky brightness ULR 15% -> 0% Factor 2 decrease of sky brightness

  14. Thus ….. Shielding of fixtures is NECESSARY AND VERY effective (up to factor ~ 7-8) ButALSO REDUCTIONof: the amount of illuminated surfaces the intensity of lighting

  15. Effect of weather

  16. Influence meteo : visibility

  17. Clouds Kas 375 x 375 m, 6100 lux, afstand 1500m, zicht 10km, wolken 600m

  18. So….. Less visibility = higher dust concentration (haze, smog) = more droplets (fog) At larger distances : darker At shorter distances : lighter Also in the case of clouds

  19. Knowledge gaps and future goals ?

  20. Unknown How often occurs which light pollution level ? (dependent on meteo) What is the true amount of upward light? (light sources in the local situation) What measures have to be taken, where and how?

  21. Developing measures policy legislation Project ! Future goals

  22. Project 2008/2009 One year continuous monitoring sky brightness at 1 – 3 locations Measuring & modelling effects of meteo and present measures Results to be transformed into darkness protection policy

  23. To see this again ! Source: Kerry-Ann Lecky Hepburn www.weatherandsky.com

  24. Extra’s

  25. Distance relationship

  26. Light output from fixtures

  27. Direct and indirect upward light

  28. Direct and indirect upward light

  29. Shielding direct upward light Factor 2 30% -> 0% factor 8 30% -> 15% factor 4 15% -> 0% factor 2

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