An Argument for Daylighting Legislation Because of Health

Abstract

Industry The Illuminating Engineering Society of North America (IESNA) is the professional body that sets building illumination standards for the US. Until 1979, IESNA had been publishing single-value illu-minance recommendations based on a method estab-lished by the Committee on Recommendations for Quality and Quantity of Illumination (RQQ) Report No. 1, which dated as far back as 1958, possibly even earlier (IES, 1958; 1980). Since then, it has become apparent to IESNA that such single-value recommen-dations were no longer valid, and they have moved towards prescribing a range of illuminance levels based on the nature of visual task, the age of the building occupants, surface reflectance, and the im-portance of speed and accuracy for performing the task. These levels are implicitly intended to be mini-mum average target levels and are based solely on a visual performance requirement. But even from the single aspect of visual performance, one can argue that an illuminance-based yardstick, alone, is not ad-equate to ensure proper illumination (Boubekri, 1999). There are also qualitative criteria and guide-lines known to professionals that pertain to other fac-tors, such as color properties of light. These criteria, however, remain, at best, merely recommended prac-tices and not enforceable standards. The use of visual performance as the single crite-rion for prescribing Illuminance levels, along with the concern about lighting's high energy consumption in non-residential buildings and the development of more efficient technologies have caused the require-ments for prescribed illuminance levels to decrease over the last five or six decades (IES, 1958; 1980) . However, neither the lighting design guidelines nor the illumination standards address health issues re-lated to light and building occupants despite the large body of scientific evidence associating light to sev-eral human health aspects. Light levels that are con-sidered as therapeutic for a variety of illnesses such as to combat seasonal affective disorders, depression, to supply the necessary light levels for photosynthe-sis to facilitate vitamin D secretion within human body, tend to be many fold higher than the indoor recommended levels for illumination (Boubekri, 2004). Let us first say that in order for any daylighting legislation to be effective, it must require not only ad-equate amount of daylight in a particular room but also specify their duration. Daylight is dynamic and constantly changing. Prescriptions ought to be made according to functional requirements of the room, seasonal variations, the geographical and climatic conditions of where the building is situated and the users' needs. Within this context, we see that legisla-tion that requires architects to design for certain pre-scribed daylight levels inside buildings does not cur-rently exist. The latest IESNA recommended practice for daylighting is completely silent when it comes to daylighting regulation (IESNA, 1999). Perhaps one of the reasons is due to the complexity of the prob-lem. If it were to be prescribed, daylighting must be specified both in terms of illumination level and du-ration of illumination. The impact this will have on fenestration design and building design may cause another set of problems that the industry may not be ready to deal with. A review of building codes in most countries shows that there are not any building codes that assign mandatory illumination levels for buildings (Boubekri, 2004). When window sizes are prescribed, they are estimated as a percentage of the wall or floor area of the room; to a large degree win-dows are provided for safety regulations as means of egress and for ventilation in case of fire but not for mandatory daylighting. The provision of natural light is only a by-product or an added benefit. Studies suggest that one way to cultivate support for daylighting legislation is to underscore its health effects. Though they may be long term ones, they are