L ABORATORIES FOR THE 2 1 S T C ENTURY :

B EST P RACTICES

DAYLIGHTING IN LABORATORIES

Introduction

Science can improve our lives dramatically, and even change the world as we know it. Therefore, it is important to

provide scientists and other researchers with laboratories that foster innovation and enhance performance. One way to

do this is by designing and building laboratories that make good use of natural light, or daylighting. Daylighting not

only saves energy, it also helps to provide an interior work environment that stimulates creativity and discovery. And

discovery is what research laboratories are all about.

Studies conducted in schools and retail centers show that daylighting helps to increase productivity and enhance

performance.(1,2) An increase in productivity of even 1%—as a result of providing natural light and views to the outdoors—has been known to nearly offset an organization’s annual energy costs. In addition, providing access to natural

light and exterior views in offices and labs is a good way to recruit and retain top scientists, technicians, and other key

research personnel.

Warren Gretz, NREL/PIX04715

Daylight through

clerestories and

small, stacked

windows illuminates

the interior office

area of a laboratory

building at the

National Renewable

Energy Laboratory

(NREL) in Colorado;

the towers help to

distribute heated or

cooled air. 

U.S. Department of Energy

Energy Efficiency and Renewable Energy

Federal Energy Management Program

United States

Environmental

Protection Agency
This guide to daylighting is one in a series on best

practices for laboratories. It was produced by Laboratories

for the 21st Century (“Labs 21”), a joint program of the 

U.S. Environmental Protection Agency and the U.S.

Department of Energy. Geared toward architects, 

engineers, and facility managers, these guides provide

information about technologies and practices to use in

designing, constructing, and operating safe, sustainable,

high-performance laboratories. 

Technology Description

Daylighting is the controlled entry of natural light

into a building. The use of daylighting allows occupants to

dim or turn off a building’s electric lights to save energy.

Daylighting is provided through windows, clerestories,

roof monitors, skylights, sawtooth roofs, or special lightpipe systems. To save the most energy, the designer must

integrate daylighting into the building’s overall design,

interior spaces, electric lighting system, and mechanical

systems.

Increasing the amount of daylight in a space entails

more than simply adding windows. Rather, designers

must locate and size windows and other elements to

ensure a relatively even amount of brightness in the building’s interior, avoid excess heat and glare, and minimize

the amount of bright sunlight that falls directly on work

areas.

Although information about how to use daylighting

in commercial buildings is widely available, designers of

daylighting systems for laboratories face different issues.

These differences are primarily due to the large interstitial

spaces between floors, lighting requirements in labs, and

the relative complexity of a laboratory’s electrical and

mechanical equipment and systems. 

Interstitial spaces above the ceilings in laboratories

are often large, so they can accommodate ductwork and

mechanical and electrical equipment. If space is not needed near the windows for these items, the added floor-tofloor height provides a unique opportunity for effective

daylighting. The higher that daylight can enter a space,

the farther back it can reach.

Lighting and daylighting requirements in labs can

vary widely. In some labs, access to views is desirable, but

daylighting might not be. In other labs, scientists may

require more ambient light because task lighting is a problem for them. However, sometimes it is difficult to design

for daylighting in the the lab portion of a building. In that

case, the designer might want to specify daylighting for

offices and public areas, instead. In most labs, less energy

is needed for lighting than for ventilation. But in offices

and public areas, lighting typically accounts for 37% of

energy consumption, and daylighting helps to reduce

both the lighting load and the cooling load. 

Given the complex mechanical, electrical and plumbing (MEP) systems in labs, integrating daylighting into the

design of a laboratory building is more challenging than 

it is for other building types. For example, MEP systems

may represent up to 50% of a lab’s construction budget,(3)

whereas these systems typically represent 20%–25% in an

office building. 

Some designers might be put off by daylighting’s

seeming complexities. However, armed with information

about where to start and how to use it, they could soon

make daylighting a “standard practice” for new laboratory buildings.

Daylighting within a space comes from three sources:

(1) exterior light reflected into a building from the ground,

pavement, adjacent buildings, and other objects; (2) direct

light from the sun and sky, which is typically blocked from

occupied space because of heat gain, glare, and ultraviolet

(UV) degradation issues; and (3) internal light reflected 

off walls, ceilings, and other interior surfaces.(4) The most

common daylighting approaches make use of side lighting, top lighting, and atria; other techniques can be used,

as well.

Side lighting. In side lighting, light enters a space

from windows below ceiling height, for views and daylight. It is a very common daylighting technique.

Horizontal strip windows are often used because they

provide more uniform daylight than individual windows.

Also, windows located higher in a space allow daylight 

to penetrate the interior of the space to a greater depth. 

If possible, separate windows should be used for views

and for daylighting, because the optimal properties of the

glazings are different for each use (see box on page 7).

The building section shown in Figure 1—which

includes a light shelf, a view window, and a clerestory

window—illustrates a rule of thumb for daylighting the

south side of a building: the distance that daylight can

extend into an interior space is equal to 1.5 to 2 times the

distance (d) from the floor to the top of the window.(5)

Adding a light shelf distributes the illumination better 

and reduces glare, because light shelves help the light

bounce off the ceiling. Exterior light shelves provide more

shade and less glare than interior light shelves do, but

both are best for year-round light distribution. Without 

a light shelf, the distance to which daylight can extend

into the space is no more than 1.5 times d. If the light shelf

has a reflective top surface, the daylit zone can be up to

2.5 times d. 

2 LABS FOR THE 21ST CENTURY
Figure 1 shows the ceiling sloping downward and

away from the window. This improves the quality of light

in the space because the sloped ceiling allows light to diffuse uniformly. A flat ceiling would be darker near the

center. In the configuration shown, ideally the view window has a lower visible transmittance (VT) than the glass

in the window above the light shelf. (See the box on page 7

for definitions of VT and other terms.)

Performance issues usually depend on orientation. In

the northern hemisphere, south-facing windows require

horizontal overhangs, external light shelves, or internal

and external light shelves to control glare and heat gain.

North-facing windows do not require shading, but they

experience greater thermal losses during the heating season, which can cause comfort problems. These can be minimized by using windows on the north side with a lower

U-value or well insulated windows with low-emissivity

(low-E) coatings. East- and west-facing windows are not

recommended for daylighting because it is difficult to control glare and heat gain, especially on the west side. If

these windows are used for

daylighting, external vertical

fins for shading or recessed

windows are recommended.

Figures 2 and 3 illustrate

two options for placing 

windows high in the space.

Figure 2 shows how the 

designers of Building 50 at the

National Institutes of Health

(NIH) complex in Bethesda,

Maryland, took advantage of

large floor-to-floor dimensions

to provide daylighting in a multistory lab building. Figure 3

(page 4) illustrates how the

Georgia Public Health Laboratory (GPHL) in Decatur,

Georgia, accomplished the same thing. In this example,

staff can see outside through three layers of windows.

Figure 4 (page 4) is a cross section of a planned laboratory

designed for the National Renewable Energy Laboratory

(NREL) in Golden, Colorado. It illustrates how the building provides daylighting for labs through the use of side

lighting on the north and south. 

Top lighting. For top lighting, daylight enters a space

through vertical windows located above the ceiling line.

Windows can be configured other than vertically if 

overheating can be avoided, such as by using specially

designed horizontal skylights in deep window wells. Top

lighting can be effective when windows are incompatible

with the function of the perimeter walls, when interior

spaces cannot easily accommodate side lighting, when the

design or lighting criteria make sidelighting inappropriate, or when there are security concerns. 

Daylight apertures can face north or south. Baffles

under the roof monitors or deep window wells can be

LABS FOR THE 21ST CENTURY 3

1.5–2.0 (d)

d Daylit zone

Daylight

window

Light

shelf

View

window

Figure 1. This section drawing illustrates a rule of thumb in designing for daylighting.

Interstitial Level

Curved High Ceiling

Work Stations

Daylight 

through

large

doubleheight

windows

Laboratory

Aisle

Equipment Laboratory

Room 03094301m

Figure 2. This cross section and photo of laboratories and work stations in Building 50 of the NIH complex shows how daylighting is

achieved through double-height windows.

Don Prowler & Associates/PIX10304

Courtesy of HLM Design, Inc.
Office

Office

Clerical

Office

Lab

Classroom

Service

corridor Lab support

Receiving

used to diffuse and reflect light in the space. Top lighting

can also be provided with stepped clerestory windows,

sawtooth or roof monitors, or horizontal window wells.

Figure 5 shows top lighting in a classroom building on the

Colorado School of Mines campus in Golden, Colorado.

Light is diffused through a perforated metal ceiling; this

prevents glare caused by direct sunlight on computer

screens. A cross section of this building is shown in

Figure 6.

Atria. Adding an atrium is a good way to increase the

amount of space that receives natural light in a building.

An atrium is often a central area one or more stories high

(depending on the building’s height) with side lighting or

top lighting. Atria are used for daylighting in Pharmacia’s

Building Q, a pharmaceutical research laboratory in

Skokie, Illinois. 

Other techniques. Not all buildings or sites are optimal for daylighting. A square building, or one with a long

axis running north and south, is not optimal. In both cases,

there is more east- and west-facing glass than is best for a

daylit building. Even so, some techniques can be helpful.

For example, designers can orient top lighting to face

north and south. Figure 7 is a floor plan of Donald Bren

Hall, a classroom and lab building in Santa Barbara,

California. In this building, the windows in the office are

oriented at an angle from the wall to take advantage of 

the primarily southern light. Another technique is to use

vertical or egg-crate-shaped shading devices and selective

surface glazing to reduce heat gain on the east and west

sides while retaining some of the view to the outside. 

4 LABS FOR THE 21ST CENTURY

Lab

Lab Section

Lab Corridor

Views

outside

Views

outside

Views

outside

Figure 3. The arrows show views from the GPHL laboratory through either two or three sets of windows.

Figure 4. Daylighting will enter NREL’s planned lab building primarily through clerestory windows on the north and south. Labs will also have

windows for views to the outside.
Design Considerations 

Design considerations include the building’s footprint

and mass, shading issues, placement of walls and windows, colors of interior spaces, and glazing properties.

Integrating daylighting with electric lighting, the quantity

and quality of light, and codes and standards are also

important considerations.

Building footprint and mass. As much as possible,

specify a long, narrow footprint along an east-west axis; it

is easier to daylight the north and south sides of a building

than the east and west sides. Low sun angles on the east

and west make shading difficult, so glazing

should be minimal, especially on the west side. 

Window shading. Because a well-designed

daylighting system captures indirect light from

the sun or sky, be sure to shade windows on the

south, east, and west facades from direct sunlight. Shading options include “self-shading”

windows in deep exterior wall sections, horizontal overhangs, louvers, vertical fins, and light

shelves that can be integrated into the building’s

structure. Horizontal shading devices work well

on the south facade. Architecturally, this means

that the north and south facades will look different. Vertical baffles, fins, or wing walls are recommended for east and west facades if windows

are needed there. 

Interior colors, ceiling height, and window

height. Specify light-colored interior spaces, tall

ceilings, and high windows to distribute natural

light most effectively. If private offices must be

along exterior walls with windows, specify a

horizontal band of glass that is above eye level

and adjacent to the ceiling on the walls across from the

windows. This provides workers in interior spaces with

natural light and access to views through the private

offices. Also, provide a strip of glazing above shades, so

occupants always have unobstructed windows even when

they close their shades.

Glazing properties. Choose glazing that minimizes

heating and cooling loads and maximizes visual comfort.

See the glazing performance indicators on page 7 for more

information.

LABS FOR THE 21ST CENTURY 5

Figure 6. Section through classroom block of the CTLM building at the

Colorado School of Mines, showing the top lighting.

Figure 5. Top lighting used at the Center for Technology and Learning Media (CTLM) building at the Colorado School of Mines.

Drawing courtesy of Anderson, Mason, Dale Architects Photo courtesy of Anderson, Mason, Dale Architects/PIX12815
Integration with electric lighting. Coordinate the

daylighting design with the electric lighting design so

they work together as one system. This includes defining

zones for electric lights, selecting proper task and ambient lights, and determining the best control strategy for

the lights, including photosensors and occupancy controls. Commissioning the lighting controls system to

make sure it works as designed is an important 

consideration.

Quantity and quality of light. Good daylighting

design is both an art and a science. A daylighting 

consultant is a “must” if your architect has never designed

a daylit space. Consultants use computer modeling tools

to size window openings properly, specify glazing properties, integrate daylighting with electric lights, and specify

the lighting control system. These factors ensure that interior spaces have the proper quantity as well as quality of

light for a given set of tasks. 

Proper light quality is important. Quality issues

include the uniformity of light levels and control of glare

and veiling reflections. Some variation in light levels is

pleasant, but too much causes eyestrain and unnecessary

use of shades and electric lights. A well-daylit space has

relatively even brightness, low contrast ratios (where the

illuminance levels in the space vary by less than a 3:1

ratio), and windows on two sides to provide more uniform light. Glare and veiling reflections obscure people’s

ability to see details and cause eyestrain. (Glare is extreme

brightness in the field of view; veiling reflections are

caused by vertical specular surfaces, such as computer

monitors, that reflect light into the eye.) A good daylighting system avoids these problems by minimizing or 

eliminating direct daylight on visual tasks. 

6 LABS FOR THE 21ST CENTURY

Key Questions for Daylighting

Project Teams

Questions to ask your project team:

Predesign

• What is the daylighting goal for our project? Can we set a

quantitative goal (such as to use 100% daylight for ambient

light from 10:00 a.m. to 2:00 p.m.) for each type of space—

labs, offices, public spaces, meeting rooms, and so on? 

• How can we integrate daylighting into an overall design to

ensure that this project saves energy and dollars? 

Schematic Design

• What different kinds of glass are needed for view windows

and daylighting windows at a given orientation?

• How can we ensure that light will be distributed uniformly?

• How can we simulate or model light levels to make sure our

daylighting strategy works? 

• What is the design lighting power density?

• What shading strategies will be compatible with the building’s

apperance?

Construction Documents

• Is a process for commissioning of the electric lighting

controls in response to daylight clearly defined in the

documents?

Design Development

• What type of overhead and task lighting fixtures will be

needed?

• How will lights be controlled? How many zones are needed?

Where will switches and sensors be in each zone? 

Questions to ask when selecting

daylighting consultants:

• Did previous daylit buildings that you designed perform as

expected? Can we visit them and talk to occupants?

• What simulation tools will you use to design the daylighting

system?

• How have you worked with the project design team in the

past? Are your design philosophies similar?

Figure 7. Windows for the offices of the Donald Bren Hall lab and

classroom building were oriented to take advantage of southern

light in Santa Barbara, California.
Codes and Standards 

The Illuminating Engineering Society of North

America (IESNA) defines criteria for appropriate lighting,

which depend on the nature of the tasks. IESNA recommends foot-candle levels as well as visual quality guidelines to consider in lighting design. The American Society

of Heating, Refrigerating, and Air-Conditioning Engineers

(ASHRAE) standard 90.1–1999 Table 9.3.1.2 lists lighting

power densities for various building types and suggests

1.8 watts (W) per square foot as a guideline for lighting

power density in buildings most like labs. And the

Uniform Building Code specifies the amount of glazing

that can be placed in internal walls, depending on the 

hazard rating for the laboratory building and the fire 

rating for the specific wall.

Performance Examples

The Labs 21 case studies contain examples of lighting

designs with measured electric power densities of

0.7–1.0 W per gross square foot (GSF) (see page 8 for more

information about the case studies). Monitoring results

show that lighting loads in Pharmacia’s Building Q average 1 W/GSF, and those for Sandia National Laboratories’

Process and Environmental Technology Laboratory

(PETL) are 0.75 W/GSF (though designed for 1 W/GSF).

In both buildings, electronic controls turn off lights in

unoccupied spaces. 

Daylighting can be designed as a significant source of

lighting in a space. If automatic lighting controls are used

to integrate daylighting with a building’s electric lighting

system, the average measured power density will be significantly less than the designed power density, because

electric lights will be used less during part of the day.

Designers can set quantitative performance specifications, such as the percentage of time that daylighting will

be used rather than electric lighting. If the daylighting and

electric lighting systems are well integrated, in theory the

lighting load will be close to zero between 10:00 a.m. and

2 p.m. on most workdays. Computer models can help

designers verify whether their design meets specifications.

For example, in a new laboratory being designed for one

of the Labs 21 pilot partners at NREL, designers specified

this performance goal: 100% daylighting between

10:00 a.m. and 2 p.m. in office spaces and 50% daylighting

during the same hours in laboratory spaces. A computer

simulation verified that the goal will be met.

Conclusion 

Daylighting saves energy, enhances productivity, and

reduces costs associaated with electric lighting. Daylighting

should be considered during the design phase of every

new laboratory building. The best time to address it is

during the goal-setting process, when defined, measurable

goals can be specified. A successful daylighting strategy

must be well-integrated with the building’s external

image, site, and form as well as its mechanical and electrical systems. Therefore, it is important to set a goal for 

daylighting early in an integrated design process. 

LABS FOR THE 21ST CENTURY 7

Glazing Performance Indicators

It is important to clearly specify these glazing performance

indicators when designing a daylighting system.

Visible transmittance (VT). The percentage of visible light that

will pass through glass. Glass with a relatively high VT (such 

as 0.7) has a clear appearance and is ideal for daylighting.

However, glare can be a problem for people who work near

windows made of this material. In such cases, it is better to use

view windows with well-shaded glazing or glazing with a lower

visible transmittance, to control glare.

Solar heat gain coefficient (SHGC). The fraction of incident

radiation that enters a building as heat gain. A value of 1.0

indicates that 100% of the solar gain enters the building. A value

of 0.0 indicates that no solar gain is entering the space. To

daylight a building in which heat is not wanted at any time of the

year (e.g., a large laboratory), specify glazing with a low SHGC

(e.g., 0.35). For a building designed to take advantage of passive

solar heating in winter (e.g., a very small lab), specify a glass

with a high SHGC for the south side (e.g., 0.7) and one with a

lower SHGC for the west side (e.g., 0.35). You can either specify

that the glass for the east and north sides be the same as the

glass used on the south side, or select a medium-range SHGC

value for them.

U-value. A measure of the rate of conductive heat transfer

through the glazing as a result of the temperature change

between inside and outside surfaces. A low U-value indicates 

a higher level of insulation, which is desirable for energy

efficiency.

Shading coefficient (sc). The ratio of the solar gain of a

particular glazing compared with the solar gain through clear,

single-pane glass; SC = SHGC x 1.15.

Spectral selectivity. The ability of glazing material to admit

visible light while rejecting unwanted infrared heat. Specifying

glass with a relatively high VT and a low SHGC results in a

spectrally selective glazing with good properties for daylighting

the space in a commercial building. In general, glass with a 

low-E coating, either as a film applied to the glass or suspended

between two double panes, has the right properties for

daylighting. A low-E coating transmits visible light and reflects

UV, near-infrared, and far-infrared light. Certain types of blueand green-tinted glass offer some of the same properties that

low-E coatings provide, but they also absorb rather than reflect

heat, which radiates into the building.
8

References

1. Heshong Mahone Group, Daylighting in Schools,

Paacific Gas & Electric Company, August 1999.

2. Romm, J., and W. Browning, Greening the

Building and the Bottom Line: Increasing

Productivity Through Energy-Efficient Design,

Rocky Mountain Institute, 1994.

3. Watch, Daniel, Research Laboratories, John Wiley

and Sons, 2001.

4. Hayter, Sheila J., LANL Sustainable Design Guide,

Los Alamos National Laboratory, 

LA-UR-6914, 2002.

5. O’Connor, Jennifer, with Eleanor Lee, Francis

Rubinstein, and Stephen Selcowitz, Tips for

Daylighting with Windows: The Integrated

Approach, Lawrence Berkeley National

Laboratory, LBNL-39945, 1997.

Acknowledgements

This best practices guide was written by Nancy

Carlisle of NREL; it is based on information in the

references and in "Labs 21" case studies. The following individuals provided very helpful review comments: Sheila Hayter, P.E., and Otto Van Geet, P.E.,

NREL; Geoffrey Bell, P.E., and Paul Mathew, Ph.D.,

Lawrence Berkeley National Laboratory; and Will

Lintner, P.E., U.S. Department of Energy. Paula

Pitchford, editor, and Susan Sczepanski, graphic

designer, NREL, also contributed to this guide.

For More Information

Lawrence Berkeley National Laboratory,

Daylight in Buildings: A Source Book on Daylighting

Systems and Components, http://gaia.lbl.gov/

iea21. Accessed in April 2003.

Lawrence Berkeley National Laboratory,

Daylighting and Windows, http://windows.

lbl.gov/. See especially Tips for Daylighting with

Windows: The Integrated Approach, LBNL-39945.

Accessed in April 2003.

U.S. Department of Defense et al., Whole

Building Design Guide, http://www.wbdg.org. 

Up-to-date information about integrated design

techniques, design tools, and other resources.

Accessed in April 2003.

U.S. Environmental Protection Agency and 

U.S. Department of Energy, Laboratories for the 

21st Century case studies, http://labs21.lbl.gov/

cs.html. Several case studies feature daylighting. 

For an example of the use of atria, see the study on

Pharmacia Building Q; for examples of side lighting,

see the studies on the Georgia Public Health

Laboratory, Building 50 at the National Institutes 

of Health, and the PETL at Sandia National

Laboratories, Albuquerque. Accessed in April 

2003.

On Laboratories for the 21st Centur y:

Phil Wirdzek

U.S. Environmental Protection Agency

1200 Pennsylvania Ave., N.W.

Washington, DC 20460

202-564-2094

wirdzek.phil@epamail.epa.gov

Will Lintner, P.E.

U.S. Department of Energy

Federal Energy Management Program

1000 Independence Ave., S.W. 

Washington, DC 20585

202-586-3120

william.lintner@ee.doe.gov

On Daylighting:

Nancy Carlisle, A.I.A.

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401

303-384-7509

nancy_carlisle@nrel.gov

DOE/GO-102003-1766

October 2003

Printed with a renewable-source ink on paper containing at least 

50% wastepaper, including 20% postconsumer waste

Laboratories for the 21st Century

U.S. Environmental Protection Agency

Office of Administration and Resources Management

www.epa.gov/labs21century/

In partnership with the 

U.S. Department of Energy

Energy Efficiency and Renewable Energy

Bringing you a prosperous future where energy 

is clean, abundant, reliable, and affordable

www.eere.energy.gov/

Prepared at the 

National Renewable Energy Laboratory

A DOE national laboratory