Natural-lighting Design in Architecture: Filling in the Blanks

This paper discusses the first full version of IDEA-l, a new natural-lighting design tool for the early stages of the architectural design process. This computer program, which is part of the larger IDEA+ research project, allows the user to judge the impact of natural light on his architectural design. For this purpose a number of tests are provided, covering different aspects of natural lighting. This paper will discuss each of the tests and the involved algorithms. The paper will end with a reflection on the IDEA+ project, which aims at providing a new integrated design environment for architecture. PURPOSES AND FEATURES Lighting design in architecture The past few decades an increasing number of research projects have illustrated a growing interest in natural lighting. Rising ecological awareness, combined with new insights into the psychological and physical effects of daylight and daylight deprivation, have sparked a number of research initiatives worldwide that study the potential of daylight for decreasing energy consumption, reducing carbon-dioxide emissions and improving the well-being of our buildings’ inhabitants. These projects have resulted in the definition of the daylight factor, in the introduction of standard skies and of design guidelines, in a few “manual” computation methods and, more recently, in the development of a number of computer tools. Most of these computers tools aim at an in-depth simulation of the light propagation in a building, sometimes even combined with a full thermal simulation. Examples include Radiance, Adeline, DOE2, and ESP-r. Most of these programs can produce amazing results when operated carefully, i.e. by a skilled and knowledgeable user and based on elaborate and accurate input. Because of their nature these applications are best suited for the later stages in the architectural design process. Not only is their use labor-intensive and therefore expensive, they also require a level of detail that is not available in earlier stages. Typically consultancy firms use this kind of software. As for the early stages of the architectural design process, a number of tools have been developed to compute the daylight factor, including protractors, tables, dot charts and diagrams. None of these require a high level of expertise or a high level of detail. They seem therefore excellently suited for the conceptual design stage. However, their use is not nearly as widespread as one would expect. A number of reasons can be found: their result, the daylight factor, is not very informative; the fact that all calculations have to made by hand makes them rather cumbersome to use; many designers feel they can rely upon their intuition when it comes to lighting... What does this mean for the component of lighting in architectural design? Lighting, if at all treated, is in most cases reduced to the very last stages. For artificial lighting this can seem completely justified. However, natural lighting includes a wide range of aspects that can affect design decisions as early as conceptual design. Research has shown that often very important conceptual decisions are taken based on assumptions without any form of prior assessment (de Wilde et al. 1999)(Saelens & Hens 2000). Too often poorly chosen design options are optimized, options that might have been abandoned in the conceptual design stage when looked at closely. This situation, which is not limited to lighting, cannot be justified, considering that early design decisions tend to have the greatest impact. Changing this situation is not an uncomplicated task. It involves a change in mentality on behalf of the designer, perhaps a change in the education of architects, it requires the careful study of conceptual design decisions and the availability of appropriate assessment tools. Providing one of these tools is what we aim at with the development of IDEA-l (read “idea-ell”). This program, which is part of the larger IDEA+ research project at K.U.Leuven, aims at providing a means for the designer of judging the impact of natural lighting on his design right at the beginning of the design process. Seventh International IBPSA Conference Rio de Janeiro, Brazil August 13-15, 2001