Simple Nomographs for Assessing Lighting in Urban Environments

Abstract

Incorporating different technologies and lighting techniques in the illumination of structures has allowed us to portray fantastic night time vistas of our cities. However, the success of the selected technique or technology is frequently assessed based on what the lighting does to the overall environment. At present, it is a common practice for the client or architect to require an illuminated night view of the building. These views are often used as part of the marketing strategy to promote building facilities. Alternatively, on a large scale, they can help promote buildings as city icons.

The illumination of building facades requires an appropriate selection of one or more floodlighting techniques and light sources to achieve the desired lighting effect. This selection, often driven by lighting standards and design considerations, will heavily influence the way in which that the overall lit environment will be portrayed at the end of the lighting project. Currently, tables and floodlighting techniques exist to select the recommended quantity of light and the most suitable luminaire arrangement to illuminate a façade. There is however, no direct indication of how the surrounding area will be affected when the recommended light levels are achieved on the façade.

Despite the increased importance of the floodlighting technique, the design of a good illuminated façade does not have a tradition on which to base parameters for the lighting design. This is often individually approached based on the knowledge, understanding, experience and proficiency of the lighting designer. Considering the diversity of buildings in urban environments, the selection of uncoordinated design parameters could have a significant impact on the area where the building is located. This could affect the occupant comfort and good energy management.

In light of the considerations presented above, it is only with a methodological approach that the lighting designer will be able to provide predictable and consistent results in any number of different situations. This presents an opportunity to develop a methodology to identify whether a façade is over-lit or if the proposed lighting solution is adequate for the area where it is situated.

The proposed methodology will provide a tool to estimate the potential lighting results while considering the effect on the overall environment where the building is located. When a façade is illuminated, the degree of the light experienced at street level is very much dependent upon the reflected light from the primary lit surface. This allows for a relationship based on light levels received at the surrounding street and the average illuminance level achieved on the façade.

Considering that lighting parameters such as lamp lumen output, the reflective qualities of the surface and the luminaire position are intrinsically connected to light reflections, a mathematical expression is formulated to link the relationship mentioned above with lighting design parameters through a set of nomographs. This method provides a good foundation to systematically approach lighting designs with a comprehensive procedure to link the practical lighting considerations with the lighting requirements that will provide occupant comfort and good energy management. This method will help designers to compare different lighting alternatives by analysing the lighting impact of different lit facade options at the very early stage of the lighting design process.