scope:

Background and Scope

Spatial Daylight Autonomy and Annual Sunlight Exposure are intended for application to common workplace environments and can be used for evaluating a single space or a collection of spaces across a building. The foundational research² was conducted in open offices, classrooms, meeting rooms, multipurpose rooms, library spaces, and service areas in lobbies. Therefore, the metrics are most applicable to spaces with similar visual tasks and occupancy patterns. The studied spaces were located in the continental United States, and thus are most applicable to similar latitudes (35 to 55 degrees) and for occupants with similar cultural backgrounds and experiences with daylight.

These metrics are calculated for a discrete "analysis area," as defined in Section 4.1, and address performance within a physically defined interior space. The metrics can be used to analyze daylighting performance in an existing building or in a new design, from the early conceptual stage through construction documents. They can also be used to guide design specifications for owners, building codes, and voluntary certification programs, and to inform field research and the design of optimization studies. It is for this reason that a standardized methodology and set of input parameters are presented in this document for use in applying these metrics.

It is important to acknowledge that these metrics are intended to describe an asset value (an assessment applying standardized ratings) for a given building design, based on standardized assumptions, rather than to predict the actual performance that would be determined by real-time weather and concurrent human behavior. "Asset" value refers to the value of a physical building independent of its current occupants' desires, behavior, and management. It distinguishes between the tangible aspects of building design and the impact of operational variables. In LM-83 many operational defaults are used to define a "normative" condition for general rating purposes, similar to a kilometer per liter (mjiles per gallon) rating for a car.

Producing an acceptable sDA and ASE does not guarantee a "good design," as these metrics provide only a first order-of-magnitude comparison between spaces and design strategies, and do not address important details related to the space, occupancy periods, visual tasks, building site, or thermal considerations that might affect the quality of a particular design. A more complete design study may require additional analyses or alternate assumptions than are applied in the standardized sDA and ASE metrics. The primary goal of this document, and the metrics its presents, is to create a consistent methodology that facilitates comparable reporting across research, design, and policy endeavors.

There are many things that these daylight performance metrics are not. They, and the illuminance threshold values that apply to them, are not counter to, nor do they supersede, IES task lighting criteria for these space types found in IES Recommended Practice documents. In addition, these metrics do not directly address human health outcomes, an ongoing area of research. These metrics also do not address energy performance, which would require a detailed analysis that also considered the design and operation of the electric lighting system, occupancy patterns, and the effect of the fenestration system on building heating, cooling, and ventilation. Finally, these metrics do not directly assess disability glare, discomfort glare, or veiling glare, which require a different type of analysis that is based on the luminances in an occupant's field of view.