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Guideline I.8: Daylight

Intent

To promote daylight for ambient illumination at levels and conditions known to produce physiological and psychological benefits. Daylight contributes to a perception of a “bright and cheery” workplace through provision of volumetric brightness (also called “room-surface brightness”). The important qualities of daylight are its inherent variation, power spectrum (color), and the predominantly horizontal component of its illumination vector (direction of illumination). Some studies have also shown a correlation between daylighting and improved productivity and test scores.

Required Performance Criteria

Guidelines apply to all projects designated New Buildings and for Major Renovations with glazing redesign included in project scope.

  1. In New Buildings, at least 75% of the floor area of continuously occupied spaces in the building must have a minimum daylight factor of 1% when measured without furniture and at 2 feet 6 inches above the floor. This may be demonstrated using the Daylight Factor Calculator provided in the B3 Guidelines, through daylight simulation, or physical daylight modeling. (This is recommended for Major Renovations where applicable.)
  2. In New Buildings, in every continuously occupied space with daylight, not more than 15% of the floor area shall exceed a uniformity ratio of 10:1 when measured without furniture and at 2 feet 6 inches above the floor. (This is recommended for Major Renovations where applicable.)
  3. Control direct solar penetration with fixed or operable shading devices to prevent direct sunlight from falling on the work plane beyond 4 feet from the exterior walls during the majority of operating hours.
  4. Employ automatic controls to turn off or dim the electric lights when daylighting is available. For spaces with daylight, the Window to Floor Area Ratio (WFAR) should not need to exceed 25% in order to meet daylighting criteria listed here. Note that exceeding this WFAR may introduce excess energy use and possibly glare.

A continuously occupied space is defined as a space that is occupied by one or more persons for more than one hour during days the building is in use.

Excluded from calculation of continuously occupied spaces are:

  • Spaces with uses that only require minimal lighting and in which the primary activity intended for the space would be harmed by daylight (this exclusion does not apply to spaces with ultraviolet light concerns).
  • Spaces that do not meet the minimum occupancy outlined above during daylight hours.

 

Several different software environments can calculate daylight factor and other daylighting metrics, these include:

Velux Daylight Visualizer, a simple-to-use daylight and rendering modeling environment that can be used to evaluate daylight factor and other lighting measures for complicated spaces and that works with 3D models from Autocad, Revit, Sketchup, Archicad, and others.

Diva for Rhino is a plug-in used in conjunction with the Rhinoceros NURBS modeler. It allows complex evaluations of daylight in buildings, including analysis of their surrounding environments.

DAYSIM is an analysis software that uses the Radiance engine and allows for 3D model inputs and evaluation in Rhinoceros, Sketchup, and Ecotect.

Implementation in the Design Process:

While programming the space use and arrangement of the project, identify and list continuously occupied spaces without security, hazard, or other conditions that would prevent the use of windows.

Using the Daylight Factor Calculator or other daylight simulation to establish room proportions, window area, and surface properties that satisfy the required performance criteria for each of the prototype spaces characteristic of the project’s design.

During early design use the Daylighting Factor Calculator or other daylight simulation to establish room proportions, window area, and surface properties that satisfy the required performance criteria, if this has not already been completed. Begin organizing the building volume and fenestration so as to maintain the required performance criteria. Use the output from the daylight models to check the performance periodically as the design evolves.

For each of the main prototype spaces, test and determine the implications for orientation, room proportion, window area, and finishes that achieve the performance criteria.

As the project design progresses demonstrate compliance using the Daylighting Factor Calculator, computer simulation, or physical modeling, whichever tool is appropriate. For each of the main prototype spaces, show a summary of calculations and quantitative results indicating conformance with performance criteria.

During construction observe and verify that the room, window, finishes (upon which estimated compliance was based) are proceeding according to goals and are reflected in drawings and specifications.

Measure performance criteria onsite. Develop a sampling plan to confirm daylighting performance over the first three years of occupancy. Compare performance at specific test times to what would be expected under the same conditions in the model. For example, if the onsite lighting measurements are taken at noon, on September 21, compare to the modeled condition at noon on September 21. Demonstrate that performance criteria are maintained via a sampling plan of daylighting performance over varying conditions during the first three years of occupancy.

Documentation

A Simple Daylighting Factor Calculator available in Appendix I-8 is designed to identify the physical attributes for room dimensions, surfaces, and fenestration in order to just meet the performance criteria for standard CIE overcast sky conditions. It does not currently take into account light shelves, partitions, non-orthogonal planes, significant exterior obstructions, or exterior reflecting surfaces. For such parameters that go beyond the current capability of the Daylighting Factor Calculator, physical models or computer simulations are necessary to refine the volumetric and surface attributes of the final design in order to assure compliance with the Required and Recommended Performance Criteria.

For more advanced and refined analysis, computer analysis and simulation should be used to evaluate options and create a daylighting solution. Some widely available programs are noted below. Usually, three-dimensional digital models are constructed using computer-aided design software (CAD), which is then imported into the daylighting analysis software. Such programs usually require the user to define location, sky conditions, and date and time and interior surface characteristics. Note that some programs that produce photorealistic renderings of the design do not necessarily provide accurate quantitative results.

Design:

  • I.8A: Verification and documentation that 75% of continuously occupied space has a daylight factor of 1% or greater.
  • I.8B: Verification that design does not exceed 10:1 in more than 15% of floor area.
  • I.8C: Verification that daylight penetration is controllable more than 4 feet from exterior walls during operational hours.

Final Design:

  • I.8A: Verification and documentation that 75% of continuously occupied space has a daylight factor of 1% or greater.
  • I.8B: Verification that design does not exceed 10:1 in more than 15% of floor area.
  • I.8C: Verification that daylight penetration is controllable more than 4 feet from exterior walls during operational hours.

Appendix I-8: Daylighting Factor Calculator

Velux Daylight Visualizer: https://commercial.veluxusa.com/inspiration/daylight-visualizer

ElumTools (integrated with Revit): https://apps.autodesk.com/RVT/en/Detail/Index?id=2939488134782668228&appLang=en&os=Win64

Efficient Windows Collaborative contains references, resources and simulation tools for window design and selection for daylighting: www.efficientwindows.org

Windows for High Performance Buildings contains references, resources and simulation tools for window design and selection for daylighting: www.commercialwindows.org

Radiance lighting engine: radiance-online.org

DOE Buildings Program: Daylighting http://energy.gov/eere/energybasics/articles/daylighting-basics

Building Energy Software Tools Directory: the DOE lists several hundred types of building analysis tools available to the designer, with a section on lighting, many of which include daylighting capabilities: http://buildingenergysoftwaretools.com/

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