Architectural Lighting Design
The importance of vertical illumination in a holistic lighting design methodology
Encompassing both the objective and subjective qualities of space, holistic lighting design is one which considers all aspects of the illuminated environment. Although such an approach has been proposed for some time, there still appears to be a weighted importance on illuminance levels stipulated in lighting regulations and the provision of a blanket level of horizontal task illuminance. This paper explores the importance of vertical illumination in a holistic lighting design methodology. 74 participants completed an online survey which explored this theory. Major findings and themes discussed include; consideration of the entire space beyond the provision of task illuminance; vertical surfaces as a major element in the field of view and contributor to the impression of space; and further exploration of the measured values and the distribution of (il)luminance.
Holistic lighting design is one which encompasses both the art and science components of lighting design. The art addresses the aesthetic qualities of the environment, revealing the architecture and creating a pleasant atmosphere. The science addresses the physiological needs of occupants, providing the quantity of light required by the visual system.
The quantitative approach to lighting design only addresses one half of the art and science – subjective and objective, psychological and physiological – requirements of lighting design. Task area, specifically horizontal illuminace, bias in lighting design has resulted in many environments which, although achieve the minimum task illuminance recommendations, appear under lit, dark and can be described as gloomy (Sheperd, Julian & Purcell, 1989).
A task and ambient lighting approach to lighting design which does away with blanket levels of illumination to one which provides task lighting as it is needed, with background illumination which respects the architecture and creates a pleasant environment, has the potential to reduce the energy demands of lighting and improve visual amenity (Low & Rowlands, 1996).
Existing research investigating the subjective responses to interior environments suggests that making allowances for the vertical surfaces within a space may improve the quality of the visual environment (Veitch, 2001). Combining this with the ambient and task approach, vertical illumination can potentially reduce the current energy demand of lighting, and improve the visual amenity, supporting both the art and science of holistic lighting design.
A holistic lighting design methodology is one which addresses the entire environment. It considers the architecture, the participants and how the space will be used. A review of the literature revealed that vertical illumination is an important factor which is often overlooked by many lighting designers and illuminating engineers who focus only on the provision of task lighting. Relying on task plane illuminance for lighting adequacy has often produced environments which appear under illuminated despite achieving minimum recommendations. Although the distribution of light in a space is argued to be a matter of personal preference, a number of studies revealed that the impression of brightness is more than a question of aesthetics. The light on the vertical plane has a major influence on the impression of brightness. The present research further explored the influence of vertical illumination on the impression of a space, and whether environments with a combination of task and background illuminance would be preferred to those with a blanket level of task illuminance. The research confirmed that the psychological influences of lighting design are complex and that visual adequacy is dependant on more than minimum levels of horizontal task illuminance. It is hoped that the consideration of vertical surfaces when designing the lighting for an environment will improve visual amenity of a space.