I.9 Daylight

Intent
Provide 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

1. In New Buildings, at least 75% of the floor area of continuously occupied spaces in the building shall have a minimum daylight factor of 1% when measured without furniture and at 2'6" above the floor. This may be demonstrated using the Daylight Factor Calculator provided in the 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 2'6" above the floor. (This is recommended for Major Renovations where applicable.)
3. To be considered a good daylighting design, direct solar penetration must be controlled with fixed or operable shading devices and kept from falling on the work plane beyond 4 ft. from the exterior walls during most operating hours.

For the purposes of these guidelines a continuously occupied space is defined as a space which is occupied by one or more persons for more than one hour each during days the building is in use.

Excluded from calculation of continuously occupied spaces are:

• Spaces which have 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 which do not meet the minimum occupancy outlined above during daylit hours

For new lighting scope, automatic controls should be employed to turn off or dim the electric lights when daylighting is available. Note: 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.

Compliance Tools and Resources

• Simple Daylighting Factor Calculator for a example building area with a single side with glazing and no borrowed light. See Appendix I-9.
• For more advanced and refined analysis, computer analysis and simulation may 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 (CAD) computer-aided design software that is then imported into the lighting 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 provide accurate quantitative results.