Far beyond energy savings, daylighting in buildings benefits the bottom line with productivity and health gains.

1. Daylit Spac
BY RAMANA KOTI
Far beyond energy
savings, daylighting
in buildings benefits
the bottom line
with productivity
and health gains.
©2006 ASSASSI. BNIM ARCHITECTS
The entrance lobby of the Lewis and Clark
State Office Building in Jefferson City, Mo.,
allows abundant north light for employees
and visitors alike. Studies show that employ-
ees in daylit buildings like this one are more
productive than employees working in artifi-
cially lit environments.
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2. es, Productive Places
O
ur reverence for the sun as the source of life included “health and productivity concerns and the interplay
is as old as human civilization. Even today, of natural light and building form.”
many practitioners of yoga still practice the Based on the responses of the 120 professionals who partici-
Sun Salutation (Surya Namaskara in Sanskrit), pated, the architectural and building energy-consumption-ben-
an act of physical exercise and meditation efit categories were the most relevant. This trend is further sup-
performed at sunrise. In ancient Hindu liter- ported by the fact that architects and engineering consultants are
ature, the Sun Salutation is recognized as a means to physical turning to building information modeling (BIM) that integrates
and mental well-being. daylighting design and energy performance to lay the foundation
Most people associate daylight with positive feelings. The for a good design during the early stages of a project.
news media regularly report scientific studies that acknowledge
the link between the day and night cycle and the human circa- Daylighting Studies
dian rhythms. These rhythms generally promote activity during Early daylighting studies focused exclusively on the energy
the day and sleep during the night. savings. For U.S. office buildings until the late 1970s, daylighting
Daylighting as a natural, controlled and passive strategy of illu- was generally believed to result in a 15 percent to 20 percent
minating building interiors predates the profession of building savings in energy consumption over a non-daylit building. With
design. In the recent past, however, daylighting has become an increasingly efficient light fixtures, daylighting no longer has as
inseparable part of integrated design, and different building pro- much impact on energy savings. However, during the past 15
fessionals value daylighting for different reasons. years, studies have identified significant psychological and phys-
In a recent survey on the role of daylighting in sustainable iological benefits of daylighting that translate into tangible
design by National Research Council Canada and Lawrence benefits for building occupants and owners.
Berkeley National Laboratory, researchers asked designers and While productivity benefits are hard to quantify, there are
engineers which of five benefit categories — architectural, some encouraging studies that make a strong case for daylight-
building energy consumption, cost, lighting energy savings, ing. Romm and Browning’s studies in the 1990s documented
and load management — they most closely associated with eight buildings with various energy-efficiency measures, some of
daylighting (see chart, below). The architectural category which involved incorporating daylighting through roof skylights,
sloped ceiling for indirect lighting, lightshelves and atria, among
other strategies. Companies occupying daylit buildings reported
an increase in productivity of 5 percent to 15 percent and a
reduction in absenteeism of 15 percent to 40 percent. The authors
concluded that the increased productivity resulting from improved
daylighting measures would pay for those measures in 1 to 4.5
years. In another study done in 1998, Professor Harvey Bryan, a
daylighting expert at Arizona State University, demonstrated a case
in which a 0.5 percent increase in productivity could pay for the
building’s energy costs, while a 6.6 percent increase could pay for
the entire building!
Recent research by the Heschong Mahone Group for the Cal-
ifornia Energy Commission also indicates that daylighting boosts
productivity 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 views
C.F. REINHART & A. GALASIU, 2006
processed calls 7 percent to 13 percent faster than those with no
views. Office workers with the best possible view performed 10 per-
cent to 25 percent better on mental function and memory recall
tests than workers with no views.
Not surprisingly, glare affected performance adversely. The
A recent survey indicates that designers and engineers consider study also found a uniformly positive and statistically significant
architectural and building energy-consumption issues to be the most correlation between the presence of daylighting and student test
relevant benefits of daylighting in sustainable design. scores in three school districts. The “daylighting effect” was
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3. DAYLIT SPACES
attributed to quantitative and qualitative aspects such as improved ing on scale models and performed daylight-illuminance analy-
visibility, better distribution of light, better color rendition, sis using the computer simulation program called Lumen Micro
absence of flicker and highlights on three-dimensional objects. to determine the configuration of external shades and internal
light shelves. The resulting design integrates external shades on
Daylighting Design the south façade into the precast structure of the building. The
Creating visually stimulating spaces through the interplay of design is visually pleasing and maximizes the use of daylighting.
natural light and building form has historically been an impor- In an online survey conducted after they moved in, the build-
tant objective in architectural design. An architectural design for ing occupants were asked to characterize their overall level of
Phoenix’s climate, for example, would be inherently different from comfort. Categories in the survey included overall building,
a design for Chicago’s climate. The concept of “critical regional- lighting, acoustics, air quality and temperature. Eighty percent
ism,” a response to “placelessness” in architecture, offers an inter- of the respondents indicated they were comfortable or neutral
esting insight into the relationship between space and light. with overall lighting in the building, while 89 percent of the
(Placenessness refers to architecture that seems to have no rela- respondents were comfortable or neutral with the amount of day-
tionship to its location — it could be anywhere.) It argues that the light in the building. However, 43 percent noted discomfort
character of architecture in a region emerges from the way design- caused by glare, especially from the low winter sun. The build-
ers work with building shapes and the arrangement of windows ing owners and BNIM are conducting further tests to determine
to deal with light and climate control. It advocates the use of con- how to mitigate the glare.
trolled daylight that, for example, causes the exhibition volume
in an art gallery to change with time, season and humidity, as LEED and Daylighting
opposed to the exclusive use of artificial light. Daylighting has always been an important part of the U.S.
When BNIM Architects began work on the design of the Lewis Green Building Council’s (USGBC’s) Leadership in Energy and
and Clark State Office Building for the Missouri Department of Environmental Design (LEED) rating system. Up to 2 points may
Natural Resources in Jefferson City, the expression of the design be earned for daylighting and views. The USGBC has made some
evolved from similar objectives. From conception, optimal depth changes to the metrics to qualify for points. While LEED version
of the available floorspace, orientation, solar control and access 2.1 and 2.2 relied on the same daylight factor calculation to demon-
to daylighting were integral to the sustainable strategies under strate compliance for the credit Indoor Environmental Quality
consideration. BNIM conducted solar studies on site, did solar test- (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-
Daylighting Glossary light in 75 percent of regularly occupied areas at the workplane level
(30 inches, or 76 centimeters, above the floor) at noon on the
Daylight Factor: The ratio of the internal illuminance at a equinox using computer simulation or demonstration of the same
point in a building to the unshaded, external horizontal through measurements on site (on a 10-foot, or 3-meter, grid).
illuminance under a CIE overcast sky. (CIE is the Commission The LEED Reference Guide, in the credit EQ 8.1, illustrates vari-
Internationale de l’Eclairage, which has developed a series of ous daylighting strategies and cautions against unwanted glare. The
mathematical models of ideal luminous distributions under guide suggests ways in which designers can avoid glare. Despite its
different sky conditions.) usefulness, the intent of the LEED credit is to quantitatively assess
Daylight Autonomy: For a sensor point, it is the percentage daylight availability at an instant in the year, for a building in which
of occupied times of the year when the minimum illuminance daylighting design intent may or may not be based on robust
requirement at the sensor is met by daylight alone. scientific principles. Because such a framework for assessing a
building’s performance is often interpreted by design teams as a
Useful Daylight Illuminances: Aims to determine when daylight
design guide, the metrics used by it assume critical importance.
levels are useful for the occupant, in terms of being neither too
The Lewis and Clark building achieved both the EQ credits per-
dark nor too bright (between 100 lux and 2000 lux).
taining to daylight and views. In the credit EQ 8.1, the metric for
Continuous Daylight Autonomy: Similar to Daylight Autonomy demonstrating daylight availability, the building achieved a 2 per-
except partial credit is attributed to time steps when daylight cent daylight factor in 75 percent of the regularly occupied spaces,
illuminance lies below the minimum illuminance level. which exceeds the LEED requirements. The building was award-
Daylight Saturation Percentage: The daylight saturation ed a LEED Platinum certification last year, making it only one of
percentage for 40 foot-candles (DSP40 ) to 400 foot-candles 21 facilities that have earned USGBC’s highest level of recognition
(DSP400) is the percent of hours and the percent of classroom for new construction to date.
floor area between 8 a.m. and 3 p.m., Monday through Friday,
from Aug. 15 through June 15 when daylight provides at Other Metrics and Tools
least 40 foot-candles or more of illumination at a work plane Daylight factor, one of the metrics used by LEED, is the most
located 30 inches (76 centimeters) above the floor. Achieving widely used metric for daylighting-performance analysis and pre-
a DSP of 400 is an indicator of over-lighting and glare, and diction. Daylight factor originated as a minimum legal lighting
requirement and is based on the worst-case scenario — a uniform-
is therefore penalized.
ly overcast sky. It did away with the complications of having to
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4. ©2005 SINCLAIR, COURTESY OF BNIM ARCHITECTS
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 structure
of the building.
DRAWN BY JEREMY CORDELL, BNIM ARCHITECTS
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 factor
approach does not result in realistic performance expectations.
They suggest metrics that account for varying climate conditions
throughout the year. Such metrics also consider the occupancy
profiles of a building.
Annual daylight prediction through computer simulation has
become more accurate, down to the time step of an hour or less.
Higher accuracy of such daylight prediction has ceased to mean
Two views of the south façade of the Lewis and Clark State Office longer simulation duration. Computer simulation also accommo-
Building, which uses the precast structure of the building to control
dates complex but critical concepts such as user behavior in con-
solar gain and allow daylight penetration.
trolling blinds. The ability to predict daylight accurately on an
hourly basis with stress on climate-based design has given rise to
deal with dynamically changing sky conditions. Daylight-factor metrics such as daylight autonomy, useful daylight illuminances
calculation for a space does not take orientation into considera- and continuous daylight autonomy (see “Daylighting Glossary,”
tion and disregards shading and glare-control strategies, which are facing page). California’s Collaborative for High Performance
not concerns in an overcast-sky condition. The premise was that Schools, which offers guidance for designing high-performance
if the design is good for the worst-case scenario, it must be good schools, suggests another metric called daylight saturation percent-
for all other conditions. Daylight factors for different design con- age. A designer can optimize a particular design based on these
ditions, such as geometry and surface properties, vary and can help metrics or compare different design alternatives to arrive at the
in narrowing down the best design solution. The calculation is most suitable one.
simple, intuitive and easy to communicate among design teams. Radiance, a UNIX-based daylighting- and lighting-simulation
Not all experts agree that daylight factor is the best way to software, is another highly regarded tool that facilitates accurate
measure daylighting performance. Christoph Reinhart, John modeling. The use of climate-based daylighting metrics is evident
in one case study by Matt Franks, a lighting consultant with
Arup Lighting in New York. The case study illustrates the use of
Daylighting Design Resources Radiance-based DAYSIM software to optimize the predicted illu-
IESNA Lighting Handbook, Illuminating Engineering Society of minance levels on a typical art hanging point in a museum
North America: www.iesna.org gallery on an annual hourly basis.
One other tool worthy of note is The Green Guide for Health
Daylight in Buildings, Lawrence Berkeley National Laboratory
Care, a joint project of the Center for Maximum Potential Build-
(LBNL): http://gaia.lbl.gov/iea21/
ing Systems and Health Care Without Harm. This self-certifying
Energy Design Resources Design Brief: sustainable design toolkit for the healthcare sector draws upon
www.energydesignresources.com/docs/db-01-daylighting.pdf research and resources in the sector to maximize the benefits of
Collaborative for High Performance Schools Best Practices Manual: increased daylighting, connectivity with the outside world and
www.chps.net/manual/documents/BPM_2006_Edition/ lighting design that reinforces circadian rhythms for caregivers,
CHPS_II_2006_Lighting_and_Daylighting.pdf patients and families. It deals with operations both in existing
Dynamic Daylight Performance Metrics for Sustainable Building facilities and in new construction and is structured to work along-
side the LEED rating system.
Design, National Research Council of Canada:
As designers and engineers continue to develop creative
http://irc.nrc-cnrc.gc.ca/pubs/fulltext/nrcc48669/
designs, reliable metrics and user-friendly computer simulation
“Building Information Modeling and Green Design,” Environ- tools, good daylighting design has become more accessible than
mental Building News, May 2007: www.buildinggreen.com/ ever. The shift toward increased use of clean, sustainable, inex-
auth/article.cfm?fileName=160501a.xml haustible solar energy indicates our willingness to come full cir-
Matt Frank’s and others’ studies on the Radiance Presentation cle and tap a resource that has been there all along.
Archive from the National Research Council Canada
http://irc.nrc-cnrc.gc.ca/ie/light/RadianceWorkshop2005/ Ramana Koti is a sustainable building analyst with BNIM Architects
and a LEED-accredited professional. Contact him at rkoti@bnim.com.
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