Advantages and possibilities of light pollution modelling (LPM)
LPM gives insight how light from light sources propagates in the atmosphere, which light sources contribute most to light pollution and what measures for reduction of light pollution are the most effective.
Basics of LPM
Light from light sources is scattered in the atmosphere to an observer by air molecules, dust particles, water droplets and clouds. The effect of scattering by air molecules gives our sky a blue colour during daytime. By modelling this propagation and scattering of artificial light, the brightness of the night sky brightness as seen by an observer can be calculated. Factors that influence the sky brightness are among others the visibility range, the wavelength of light and of course the specific output characteristics of light sources, such as light intensity, the amount and direction of upward light.
General results from LPM
Air molecules scatter the light in all directions, while small dust (haze) particles scatter the light predominantly in a forward direction and are about a factor 100 more effective in light scattering than air molecules.
Light that emanates useless from fixtures directly into the atmosphere and reflected light from vertical surfaces (walls) generates the so called “long-distance” light pollution. This is enhanced due to the strong forward light scattering of dust particles. Shielding of direct upward light and reduction of reflected light from vertical surfaces is a very effective way in reducing the “long-distance” light pollution. No light above the horizontal should be emitted.
Ground reflected light generates the light pollution “overhead”. Reduction of the amount of illuminated ground surface and the intensity of this illumination reduces the “overhead” light pollution.
Light pollution increases at shorter distances from light sources when the visibility decreases, for example during hazy conditions. This explains the increase in light pollution in cities and in the neighbourhood of cities when visibility decreases.
Number and differences between Light Pollution Models
To this date only a handful of Light Pollution Models exists, which are owned by private persons or institutes. In general these Light Pollution Models employ the same physical laws for light scattering in the atmosphere; however the models differ in the way of the degree of development and complexity. For example, the way of modelling the light output characteristics of fixtures, the degree of modelling the surrounding effects (such as shielding by houses, trees and reflection of walls), dust layers, wavelength of light, clouds and so on.
Applications of LPM
LPM is increasingly used as a tool to calculate the impact of light from greenhouses, strobe light of wind parks, greenhouses, and industrial areas and so on. In the Netherlands light pollution modelling is used in obligatory Environmental Impact Assessments for the light impact on the surroundings by greenhouses.
Reference and contact
The effects and results presented here were obtained by a light pollution model, in which most of the described parameters are incorporated. Contact firstname.lastname@example.org.