Ground Factors, Luminaires and Light Pollution Potential in Landscape Lighting Design

Light pollution, a new environmental problem, significantly influences the sustainability of an urban area on basis of ecological stability, human well-beings and energy conservation. This study analysed the impact of ground surface reflectances and three outdoor lighting fixtures on the potential of lighting pollutions in the landscape lighting design in Beijing. Seven fundamental ground surfaces found in landscape sites were investigated as the follows: new snow (reflectance 0.8), old snow (reflectance 0.5), white sand (reflectance 0.4), grey earth (reflectance 0.3), grey paving (reflectance 0.2), grass and green vegetation (reflectance 0.1), and water surface (reflectance 0.05). A test plot, covered by the seven materials and lit by three typical outdoor pole luminaires, was used to check how much light would be reflected from the ground. The potential of light pollution, therefore, could be evaluated according to the surface luminance of the landscape plot. Radiance, a state-of-the-art backward ray tracing technique, was adopted to simulate the absolute luminance and its distributions at the plot. Several findings have been given: it is necessary to check the reflected light from the ground even though a full cutoff luminaires were installed; combined with a specific luminous intensity distribution of luminaire, however, a higher surface reflectance could make it more difficult to shield the reflected light from ground.