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Far beyond energysavings, daylightingin buildings benefitsthe bottom line with productivityand health gains.

Daylit SpacBY RAMANA KOTI

The entrance lobby of the Lewis and ClarkState Office Building in Jefferson City, Mo.,allows abundant north light for employeesand visitors alike. Studies show that employ-ees in daylit buildings like this one are moreproductive than employees working in artifi-cially lit environments. ©

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Our reverence for the sun as the source of lifeis as old as human civilization. Even today,many practitioners of yoga still practice theSun Salutation (Surya Namaskara in Sanskrit),an act of physical exercise and meditationperformed at sunrise. In ancient Hindu liter-

ature, the Sun Salutation is recognized as a means to physicaland mental well-being.

Most people associate daylight with positive feelings. Thenews media regularly report scientific studies that acknowledgethe link between the day and night cycle and the human circa-dian rhythms. These rhythms generally promote activity duringthe day and sleep during the night.

Daylighting as a natural, controlled and passive strategy of illu-minating building interiors predates the profession of buildingdesign. In the recent past, however, daylighting has become aninseparable part of integrated design, and different building pro-fessionals value daylighting for different reasons.

In a recent survey on the role of daylighting in sustainabledesign by National Research Council Canada and LawrenceBerkeley National Laboratory, researchers asked designers andengineers which of five benefit categories — architectural,building energy consumption, cost, lighting energy savings, and load management — they most closely associated withdaylighting (see chart, below). The architectural category

included “health and productivity concerns and the interplayof natural light and building form.”

Based on the responses of the 120 professionals who partici-pated, the architectural and building energy-consumption-ben-efit categories were the most relevant. This trend is further sup-ported by the fact that architects and engineering consultants areturning to building information modeling (BIM) that integratesdaylighting design and energy performance to lay the foundationfor a good design during the early stages of a project.

Daylighting StudiesEarly daylighting studies focused exclusively on the energy

savings. For U.S. office buildings until the late 1970s, daylightingwas generally believed to result in a 15 percent to 20 percent savings in energy consumption over a non-daylit building. Withincreasingly efficient light fixtures, daylighting no longer has asmuch impact on energy savings. However, during the past 15years, studies have identified significant psychological and phys-iological benefits of daylighting that translate into tangible benefits for building occupants and owners.

While productivity benefits are hard to quantify, there aresome encouraging studies that make a strong case for daylight-ing. Romm and Browning’s studies in the 1990s documentedeight buildings with various energy-efficiency measures, some ofwhich involved incorporating daylighting through roof skylights,sloped ceiling for indirect lighting, lightshelves and atria, amongother strategies. Companies occupying daylit buildings reportedan increase in productivity of 5 percent to 15 percent and areduction in absenteeism of 15 percent to 40 percent. The authorsconcluded that the increased productivity resulting from improveddaylighting measures would pay for those measures in 1 to 4.5years. In another study done in 1998, Professor Harvey Bryan, adaylighting expert at Arizona State University, demonstrated a casein which a 0.5 percent increase in productivity could pay for thebuilding’s energy costs, while a 6.6 percent increase could pay forthe entire building!

Recent research by the Heschong Mahone Group for the Cal-ifornia Energy Commission also indicates that daylighting boostsproductivity in a variety of settings. In one test of mental func-tion and attention for office and call center workers, a 20 foot-can-dle increase in daylight levels resulted in a 13 percent perform-ance improvement. Call center workers with the best viewsprocessed calls 7 percent to 13 percent faster than those with noviews. Office workers with the best possible view performed 10 per-cent to 25 percent better on mental function and memory recalltests than workers with no views.

Not surprisingly, glare affected performance adversely. Thestudy also found a uniformly positive and statistically significantcorrelation between the presence of daylighting and student testscores in three school districts. The “daylighting effect” was

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es, Productive Places

A recent survey indicates that designers and engineers considerarchitectural and building energy-consumption issues to be the mostrelevant benefits of daylighting in sustainable design. C

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ing on scale models and performed daylight-illuminance analy-sis using the computer simulation program called Lumen Microto determine the configuration of external shades and internallight shelves. The resulting design integrates external shades onthe south façade into the precast structure of the building. Thedesign is visually pleasing and maximizes the use of daylighting.

In an online survey conducted after they moved in, the build-ing occupants were asked to characterize their overall level ofcomfort. Categories in the survey included overall building,lighting, acoustics, air quality and temperature. Eighty percentof the respondents indicated they were comfortable or neutralwith overall lighting in the building, while 89 percent of therespondents were comfortable or neutral with the amount of day-light in the building. However, 43 percent noted discomfortcaused by glare, especially from the low winter sun. The build-ing owners and BNIM are conducting further tests to determinehow to mitigate the glare.

LEED and DaylightingDaylighting has always been an important part of the U.S.

Green Building Council’s (USGBC’s) Leadership in Energy andEnvironmental Design (LEED) rating system. Up to 2 points maybe earned for daylighting and views. The USGBC has made somechanges to the metrics to qualify for points. While LEED version2.1 and 2.2 relied on the same daylight factor calculation to demon-strate compliance for the credit Indoor Environmental Quality(EQ) 8.1, the term “daylight factor” was renamed “glazing factor”in 2.2. A couple of additional options are available in version 2.2,including demonstrating the availability of 25 foot-candles of day-light in 75 percent of regularly occupied areas at the workplane level(30 inches, or 76 centimeters, above the floor) at noon on theequinox using computer simulation or demonstration of the samethrough measurements on site (on a 10-foot, or 3-meter, grid).

The LEED Reference Guide, in the credit EQ 8.1, illustrates vari-ous daylighting strategies and cautions against unwanted glare. Theguide suggests ways in which designers can avoid glare. Despite itsusefulness, the intent of the LEED credit is to quantitatively assessdaylight availability at an instant in the year, for a building in whichdaylighting design intent may or may not be based on robust scientific principles. Because such a framework for assessing abuilding’s performance is often interpreted by design teams as adesign guide, the metrics used by it assume critical importance.

The Lewis and Clark building achieved both the EQ credits per-taining to daylight and views. In the credit EQ 8.1, the metric fordemonstrating daylight availability, the building achieved a 2 per-cent daylight factor in 75 percent of the regularly occupied spaces,which exceeds the LEED requirements. The building was award-ed a LEED Platinum certification last year, making it only one of21 facilities that have earned USGBC’s highest level of recognitionfor new construction to date.

Other Metrics and ToolsDaylight factor, one of the metrics used by LEED, is the most

widely used metric for daylighting-performance analysis and pre-diction. Daylight factor originated as a minimum legal lightingrequirement and is based on the worst-case scenario — a uniform-ly overcast sky. It did away with the complications of having to

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Daylighting GlossaryDaylight Factor: The ratio of the internal illuminance at a point in a building to the unshaded, external horizontal illuminance under a CIE overcast sky. (CIE is the CommissionInternationale de l’Eclairage, which has developed a series ofmathematical models of ideal luminous distributions under different sky conditions.)

Daylight Autonomy: For a sensor point, it is the percentage of occupied times of the year when the minimum illuminancerequirement at the sensor is met by daylight alone.

Useful Daylight Illuminances: Aims to determine when daylightlevels are useful for the occupant, in terms of being neither toodark nor too bright (between 100 lux and 2000 lux).

Continuous Daylight Autonomy: Similar to Daylight Autonomyexcept partial credit is attributed to time steps when daylightilluminance lies below the minimum illuminance level.

Daylight Saturation Percentage: The daylight saturation percentage for 40 foot-candles (DSP40 ) to 400 foot-candles(DSP400) is the percent of hours and the percent of classroomfloor area between 8 a.m. and 3 p.m., Monday through Friday,from Aug. 15 through June 15 when daylight provides at least 40 foot-candles or more of illumination at a work planelocated 30 inches (76 centimeters) above the floor. Achieving a DSP of 400 is an indicator of over-lighting and glare, and is therefore penalized.

attributed to quantitative and qualitative aspects such as improvedvisibility, better distribution of light, better color rendition,absence of flicker and highlights on three-dimensional objects.

Daylighting DesignCreating visually stimulating spaces through the interplay of

natural light and building form has historically been an impor-tant objective in architectural design. An architectural design forPhoenix’s climate, for example, would be inherently different froma design for Chicago’s climate. The concept of “critical regional-ism,” a response to “placelessness” in architecture, offers an inter-esting insight into the relationship between space and light.(Placenessness refers to architecture that seems to have no rela-tionship to its location — it could be anywhere.) It argues that thecharacter of architecture in a region emerges from the way design-ers work with building shapes and the arrangement of windowsto deal with light and climate control. It advocates the use of con-trolled daylight that, for example, causes the exhibition volumein an art gallery to change with time, season and humidity, asopposed to the exclusive use of artificial light.

When BNIM Architects began work on the design of the Lewisand Clark State Office Building for the Missouri Department ofNatural Resources in Jefferson City, the expression of the designevolved from similar objectives. From conception, optimal depthof the available floorspace, orientation, solar control and accessto daylighting were integral to the sustainable strategies underconsideration. BNIM conducted solar studies on site, did solar test-

deal with dynamically changing sky conditions. Daylight-factorcalculation for a space does not take orientation into considera-tion and disregards shading and glare-control strategies, which arenot concerns in an overcast-sky condition. The premise was thatif the design is good for the worst-case scenario, it must be goodfor all other conditions. Daylight factors for different design con-ditions, such as geometry and surface properties, vary and can helpin narrowing down the best design solution. The calculation issimple, intuitive and easy to communicate among design teams.

Not all experts agree that daylight factor is the best way tomeasure daylighting performance. Christoph Reinhart, John

Mardaljevic and Zack Rogers, daylighting specialists at the Nation-al Research Council Canada, De Montfort University and Archi-tectural Energy Corp., respectively, argue that the daylight factorapproach does not result in realistic performance expectations.They suggest metrics that account for varying climate conditionsthroughout the year. Such metrics also consider the occupancyprofiles of a building.

Annual daylight prediction through computer simulation hasbecome more accurate, down to the time step of an hour or less.Higher accuracy of such daylight prediction has ceased to meanlonger simulation duration. Computer simulation also accommo-dates complex but critical concepts such as user behavior in con-trolling blinds. The ability to predict daylight accurately on anhourly basis with stress on climate-based design has given rise tometrics such as daylight autonomy, useful daylight illuminancesand continuous daylight autonomy (see “Daylighting Glossary,”facing page). California’s Collaborative for High PerformanceSchools, which offers guidance for designing high-performanceschools, suggests another metric called daylight saturation percent-age. A designer can optimize a particular design based on thesemetrics or compare different design alternatives to arrive at themost suitable one.

Radiance, a UNIX-based daylighting- and lighting-simulationsoftware, is another highly regarded tool that facilitates accuratemodeling. The use of climate-based daylighting metrics is evidentin one case study by Matt Franks, a lighting consultant withArup Lighting in New York. The case study illustrates the use ofRadiance-based DAYSIM software to optimize the predicted illu-minance levels on a typical art hanging point in a museumgallery on an annual hourly basis.

One other tool worthy of note is The Green Guide for HealthCare, a joint project of the Center for Maximum Potential Build-ing Systems and Health Care Without Harm. This self-certifyingsustainable design toolkit for the healthcare sector draws uponresearch and resources in the sector to maximize the benefits ofincreased daylighting, connectivity with the outside world andlighting design that reinforces circadian rhythms for caregivers,patients and families. It deals with operations both in existingfacilities and in new construction and is structured to work along-side the LEED rating system.

As designers and engineers continue to develop creativedesigns, reliable metrics and user-friendly computer simulationtools, good daylighting design has become more accessible thanever. The shift toward increased use of clean, sustainable, inex-haustible solar energy indicates our willingness to come full cir-cle and tap a resource that has been there all along.

Ramana Koti is a sustainable building analyst with BNIM Architectsand a LEED-accredited professional. Contact him at rkoti@bnim.com.

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Daylighting Design ResourcesIESNA Lighting Handbook, Illuminating Engineering Society ofNorth America: www.iesna.org

Daylight in Buildings, Lawrence Berkeley National Laboratory(LBNL): http://gaia.lbl.gov/iea21/

Energy Design Resources Design Brief:www.energydesignresources.com/docs/db-01-daylighting.pdf

Collaborative for High Performance Schools Best Practices Manual:www.chps.net/manual/documents/BPM_2006_Edition/CHPS_II_2006_Lighting_and_Daylighting.pdf

Dynamic Daylight Performance Metrics for Sustainable BuildingDesign, National Research Council of Canada:http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc48669/

“Building Information Modeling and Green Design,” Environ-mental Building News, May 2007: www.buildinggreen.com/auth/article.cfm?fileName=160501a.xml

Matt Frank’s and others’ studies on the Radiance PresentationArchive from the National Research Council Canada http://irc.nrc-cnrc.gc.ca/ie/light/RadianceWorkshop2005/

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Two views of the south façade of the Lewis and Clark State OfficeBuilding, which uses the precast structure of the building to controlsolar gain and allow daylight penetration.

The design of the Lewis and Clark State Office Building for the Missouri Department of Natural Resources in Jefferson City inte-grates external shades on the south façade into the precast structureof the building.

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