Daylighting
and
Lighting
Control
I. Definition and Description
Daylighting is the controlled admission of natural light into a space through windows to reduce
or eliminate electric lighting. By providing a direct link to the dynamic and perpetually evolving
patterns of outdoor illumination, daylighting helps create a visually stimulating and productive
environment for building occupants.
Proper daylighting design involves more than just adding windows or skylights to a space. It is
the careful balancing of heat gain and loss, glare control, and variations in daylight availability.
For example, successful daylighting designs will invariably pay close attention to the use of
shading devices to reduce glare and excess contrast in the workspace. Additionally, window
size and spacing, glass selection, the reflectance of interior finishes and the location of any
interior partitions must all be evaluated.
In large measure, the art and science of daylighting is not so much how to provide enough
daylight to an occupied space, but how to do so without any undesirable side effects.
II. Impact on Navy Building Energy Performance Goals
A. Daylighting has the potential to significantly reduce operating costs. Electric lighting accounts
for 35 to 50 percent of the total electrical energy consumption in commercial buildings. By
generating waste heat, lighting also adds to the loads imposed on a building's mechanical
cooling equipment. The energy savings from reduced electric lighting through the use of
daylighting strategies can directly reduce building cooling energy usage an additional 10 to 20
percent.
B. Consequently, for many institutional and commercial buildings, total energy costs can be
reduced by as much as one third through the optimal integration of daylighting strategies.
C. Among the primary types of Navy and Marine Corps buildings that can benefit from the
application of daylighting are:
•
Administration buildings
•
Offices
•
Warehouses
•
Maintenance facilities
III. Daylighting Fundamentals
It is important to appreciate that the daylighting design process involves the integration of many
disciplines including architectural, mechanical, electrical, and lighting. These design team
members need to be brought into the process early to ensure that daylighting concepts and
ideas are carried throughout the project.
A. Concepts
1. An awareness of basic visual acuity and performance issues is essential to an effective
daylighting design.
Veiling Reflections:
Veiling reflections of high brightness light sources off specular (shiny) surfaces
obscure details by reducing contract. They should be avoided, particularly
where critical visual tasks occur.
Distribution:
Introduce as much controlled daylight as deep as possible into a building
interior. The human eye can adjust to high levels of luminance as long as it is
evenly distributed. In general, light which reaches a task indirectly (such as
having bounced from a white wall) will provide better lighting quality than light
which arrives directly from a natural or artificial source.
Glare:
The aim of an efficient daylighting design is not only to provide illuminance
levels sufficient for good visual performance, but also to maintain a comfortable
and pleasing atmosphere. Glare, or excessive brightness contrast within the
field of view, is an aspect of lighting that can cause discomfort to occupants.
The human eye can function quite well over a wide range of luminous
environments, but does not function well if extreme levels of brightness are
present in the same field of view.
Variety:
Some contrast in brightness levels may not be undesirable. Dull uniformity in
lighting can lead to tiredness and lack of attention-neither of which is
compatible with a productive environment. Often times a good daylighting
solution will integrate a "blast" of beam daylight in a circulation area for visual
interest and to help lead occupants through a building. The human eye is
naturally attracted to this bright area and can be useful in guiding people down
an otherwise banal corridor.
2. Good daylighting requires attention to both qualitative and quantitative aspects of design.
Make sure the combination of natural and artificial sources provides adequate light levels for the
required task.
•
The Illuminating Engineering Society of North America publishes a industry-standard
method for determining recommended illuminance levels (expressed in units of
footcandles, or fc) for various tasks.
•
For office spaces, the General Services Administration has interpreted the IES method
to recommend a minimum of 50 footcandles on an imaginary desk-height horizontal
"work surface." Nevertheless, when used in conjunction with indirect an ambient lighting
system and direct task lighting, a high-quality daylighting design can be achieved with
ambient lighting levels of 30 footcandles or less.
3. To be effective, daylighting must be integrated with electric lighting design. In particular,
daylighting must be coupled with efficient electric lighting controls if net energy savings are to be
realized.
•
As part of a daylighting design, consider the use of continuously dimming fixtures
controlled by luminous sensors.
B. Design Recommendations
A number of design strategies should be understood and explored during the design process.
These strategies are briefly described below.
•
Increase perimeter daylight zones-extend the perimeter footprint to maximize the usable
daylighting area.
•
Allow daylight penetration high in a space. Windows located high in a wall or in roof
monitors and clerestories will result in deeper light penetration and reduce the likelihood
of excessive brightness.
•
Reflect daylight within a space to increase room brightness. A lightshelf, if properly
designed, has the potential to increase room brightness and decrease window
brightness.
•
Slope ceilings to direct more light into a space. Sloping the ceiling away form the
fenestration area will help increase the surface brightness of the ceiling further into a
space.
•
Avoid direct beam daylight on critical visual tasks. Poor visibility and discomfort will
result if excessive brightness differences occur in the vicinity of critical visual tasks.
•
Filter daylight. The harshness of direct light can be filtered with vegetation, curtains,
louvers, or the like, and will help distribute light.
•
Understand that different building orientations will benefit from different daylighting
strategies; for example light shelves which are effective on south-facades are often
ineffective on the east or west elevations of buildings.
All drawings on this page reprinted with permission from "Daylighting
Performance and Design" by Gregg Anders
IV. Materials and Methods of Construction
1. Exterior Shading and Control Devices: In hot climates, exterior shading devices often work
well to both reduce heat gain and diffuse natural light before entering the work space. Examples
of such devices include light shelves, overhangs, horizontal louvers, vertical louvers, and
dynamic tracking or reflecting systems.
2. Glazing Materials: The simplest method to maximize daylight within a space is to increase the
glazing area. However, three glass characteristics need to be understood in order to optimize a
fenestration system: U-value, Shading Coefficient, and Visible Transmittance.
•
U-value represents the rate of heat transfer due to temperature difference through a
particular glazing material.
•
Shading Coefficient (SC) is a ratio of solar heat gain of a given glazing assembly
compared to double-strength, single glazing. [NB: A related term, Solar Heat Gain
Factor (SHGF), is beginning to replace the term Shading Coefficient]
•
Visible Transmittance (Tvis) is a measure of how much visible light is transmitted
through a given glazing material.
Glazings can be easily and inexpensively altered to increase both thermal and optical
performance. Glazing manufacturers have a wide variety of tints, metallic and low-emissivity
coatings, and fritting available. Multi-paned lites of glass are also readily available with inert-gas
fills, such as argon or krypton, which improve U-values. For daylighting large buildings in most
climates, consider the use of glass with a moderate-to-low SC and relatively high Visible
Transmittance.
3. Aperture Location: Simple sidelighting strategies allow daylight to enter a space and can also
serve to facilitate views and ventilation. A rule-of-thumb is that the depth of daylight penetration
is about two and one-half times the distance between the top of a window and the sill.
4. Reflectances of Room Surfaces: Reflectance values for room surfaces will significantly
impact daylight performance and should be kept as high as possible. It is desirable to keep
ceiling reflectances over 80%, walls over 50%, and floors around 20%. Of the various room
surfaces, floor reflectance has the least impact on daylighting penetration.
5. Integration with Electric Lighting Controls: A successful daylighting design not only optimizes
architectural features, but is also integrated with the electric lighting system. With advanced
lighting controls, it is now possible to adjust the level of electric light when sufficient daylight is
available. Three types of controls are commercially available:
•
Switching controls - on/off controls simply turn the electric lights off when there is ample
daylight.
•
Stepped controls - provide intermediate levels of electric lighting by controlling individual
lamps within a luminaire.
•
Dimming controls - continuously adjust electric lighting by modulating the power input to
lamps to complement the illumination level provided by daylight.
Any of these control strategies can, and should, be integrated with a building management
system to take advantage of the system's built-in control capacity.
To take full advantage of available daylight and avoid dark zones, it is critical that the lighting
designer plan lighting circuits and switching schemes in relation to fenestration. The following
figure shows several control schemes.
6. Other Lighting Control Systems: In addition to daylight controls, other electric lighting control
strategies should be incorporated where they are cost effective, including the use of:
•
Occupancy controls - Using infrared, ultrasonic or micro-wave technology, occupancy
sensors respond to movement or object surface temperature and automatically turn-off
or dim-down luminaires when rooms are left unoccupied. Typical savings have been
reported to be in the 10 to 50 percent range depending on the application.
•
Timers - these devices are simply time clocks which are scheduled to turn lamps or
lighting circuits off on a set schedule. If spaces are known to be unoccupied during
certain periods of time, timers are extremely cost effective devices.
IV. Opportunities and Cautions [HCE: or, perhaps, Benefits and Costs]
As with all energy-efficient design strategies, there are both benefits and costs associated with
the use of daylighting.
Opportunities
•
Improved Life Cycle Cost: At an estimated incremental first cost
increase of from $0.50 to $0.75 per square foot of occupied space for
dimmable ballasts, fixtures and controls, daylighting has been shown to
save from $0.05 to $0.20 annually [in 1997 $].
•
Increased User Productivity: Daylight enlivens spaces and has been
shown to increase user satisfaction and visual comfort leading to
improved performance.
•
Reduced Emissions: By reducing the need for electric consumption for
lighting and cooling, the use of daylight reduces greenhouse gases and
slows fossil fuel depletion.
Cautions
•
Be Sure to Avoid Glare and Overheating: More windows do not
automatically result in more daylighting; Natural light has to be
controlled and distributed properly throughout the work space.
•
Ensure Lighting Controls Work: For cost savings to be realized,
controls have to be in proper functioning order. Poor installation,
commissioning or Operations and Maintenance (O&M) practices can all
lead to sub-optimum performance.
V. Analysis and Design Tools
1. Physical Modeling: The physics of illumination are such that light behaves exactly the same
way in a scaled model as it does in a full size room. Physical models can be built inexpensively
and at various stages of the design process. A number of issues can be accomplished with
physical models.
•
Photographs of the model interior can be taken to record and study various design
alternatives;
•
The effect of different glass areas and locations can be studied;
•
Using photometers, illumination levels resulting from different daylighting schemes can
be compiled and used to project energy savings.
2. Calculation Tools: Over the past 50 years many daylighting calculation tools have been
developed. These include hand methods, nomographs, and computer models to simulate both
daylighting design and its impact on the overall thermal performance of buildings. The following
table briefly describes some of the available tools.
Daylighting Nomographs (1984)
Description: A hand-method that assists designers in determining potential daylighting benefits
and costs; also offers a checking strategy for energy conservation and load management.
Cost: Free, but no technical support
Availability:
Building Technologies Program
Lawrence Berkeley Laboratory
1 Cyclotron Road, Bldg. 90-3111
Berkeley, CA 94720
510-486-4761; Fax: 510-486-4089
University of Washington Graphic Daylighting Design Method (1980)
Description: Determines daylight patterns for a room based on the proportions of the window
openings, providing illumination level, distribution, and gradient. For more information see: B.
Stein and J. Reynolds, Mechanical and Electrical Equipment for Buildings (MEEB), Eighth
Edition, John Wiley & Sons, New York, NY, 1992, or G. Z. Brown et al, Inside Out, Second
Edition, John Wiley & Sons, New York, NY, 1992.
Cost: approximately $30.00
Availability:
Department of Agriculture
Gould Hall JO-20
University of Washington
Seattle, WA 98105
Contact: Professor Marietta Millet
(206)-543-4180
AAMA Sky and Skylight Handbook (1988)
Description: Skylight design analysis with emphasis on optimizing for energy efficiency,
incorporating both a worksheet and Lotus spreadsheet (IBM PC or compatible).
Cost:$50.00/software package; $50.00/handbook; $100.00/handbook+software (half price for
AAMA Members).
Availability:
Architectural Aluminum Manufacturers Association (AAMA)
1540 E. Dundee Road, Suite 310
Palatine, IL 60067
Lumen-Micro 6 (1993)
Description: Analyzes complex interior lighting systems including daylight, direct/ indirect lighting,
mixed and even aimed luminaires. DXF file editor, user-friendly input, animated walk-through.
Limited to rectangular spaces. Requires IBM 486 with high density floppy drive, 8 MB hard disk
space, 80387 math-coprocessor, VGA or SVGA graphics FORTRAN, 2 MB RAM, MS-DOS 3.3
or later.
Cost: $595.00 $129 for upgrade from Lumen-Micro 5
Availability:
Lighting Technologies
2540 Frontier Street, Suite 107
Boulder, Colorado
(303) 449-5791; Fax: (303) 449-5864
Contact: David DiLaura
Superlite 2.0 (1993)
Description: Updated version of SUPERLITE 1.01. Now analyzes daylight and electric lighting
for various room geometries. Max 5 windows. Tabulated output, no graphics. IBM PC or
compatible with 8087 or better math-coprocessor chip. FORTRAN, MS-FORTRAN 3.2 compiler.
Cost: Free, but no technical support
Availability:
Building Technologies Program
Lawrence Berkeley Laboratory
(510) 486-4154; Fax: (510) 485-4089
Contact: Rob Hitchcock or Werner Osterhaus
DOE 2.1e (1992)
Description: Comprehensive hour-by-hour simulation; Daylighting and glare calculations
integrate with hourly energy simulation. IBM or compatible pentium is advisable.
Cost: Free from LBL in hard-to-use format; at various cost from third party vendors
Availability:
Building Technologies Program
Lawrence Berkeley Laboratory
510-486-5711; Fax: 510-486-4089
Several Third Party Vendors have produced user-friendly versions of DOE 2 for the professional
market
Radiance 2.1 (1992)
Description: A ray-tracing program that accurately predicts light levels and produces photo
realistic images of architectural space in all sky conditions. Sun Microsystems, DEC, MacIntosh
with (AUX), CRAY or other UNIX machine.
Cost: Contact LBL for current policy
Availability:
Building Technologies Program
Lawrence Berkeley Laboratory
510-486-5711; Fax: 510-486-4089
Contact: Charles Erlich
ENERGY-10
Description: An hour-by-hour simulation program designed to inform the earliest phases of the
design process. Runs on IBM-compatible platforms. Best operated with pentium or higher
processor and 16 Megs of RAM.
Cost: $250 [1997]
Availability:
Passive Solar Industries Council(PSIC) (http://www.psic.org)
1511 K Street NW, Suite 600
Washington D.C. 20005
(202) 628-7400
VII. Navy-Specific Standards
The Construction Criteria Base (http://www.ccb.org) is the source for the full text of all Federal
construction documents including Naval Facilities Guide Specifications (NFGS), Corps of
Engineers Guide Specifications (CEGS), Military Handbooks, and Military and Federal
Standards. It is available on CD-ROM and DVD from the National Institute of Building Sciences
(http://www.nibs.org) (1090 Vermont Avenue, NW Suite 700, Washington, DC 20005-4905;
(202) 289-7800; fax: (202) 289-1092. CCB is free to A/Es doing work for the Federal
Government.
VIII. Additional Resources and Training Opportunities
Ander, G. D., Daylighting Performance and Design, Van Nostrand and Reinhold, New York,
1995. This is an excellent source for daylighting design issues, tutorials on calculation
technologies, and has many case studies documented.
American Institute of Architects, Architect's Handbook of Energy Practice: Daylighting,
American Institute of Architects, Washington, DC, 1992. Part of a series of monographs by the
AIA on energy-conscious design. The text is supported with case studies of famous buildings
that utilize daylighting.
Evans, Benjamin H., Daylight in Architecture, McGraw-Hill, New York, 1971. This designoriented book is intended as a primer. It is strong on basic concepts and model testings and is a
good place to start for those entering the field.
Hopkinson, R. G., Petherbridge, P., and Longmore, J., Daylighting, University College,
London, 1966. This text is an excellent technical resource for daylighting research and design
methods, including sections on sky luminance, daylight photometry, models, and artificial skies.
Illuminating Engineering Society of North America, Recommended Practice of Daylighting,
IES, New York, 1979. This publication is a very good source for daylighting information. The
appendix goes through typical examples of the IES method.
McCluney, Ross, A Daylighting Checklist, Solar Age, April 1985, p. 84. This one-page outline
contains 15 factors to consider when employing daylighting. It contains good references to other
articles that delve into some of the factors in more detail, such as roof monitor design and
calculator programs for skylight.
Moore, Fuller, Concepts and Practice of Architectural Daylighting, Van Nostrand Reinhold, New
York, 1986. This good text on the fundamentals of daylighting is well supported with graphics.
Simpler and more direct to use than other texts on the subject, it covers all of the major issues
pertaining to daylighting.
Olgyay, Aladar, and Olgyay, Victor, Solar Control and Shading Devices, Princeton University
Press, Princeton, NJ, 1976. This classic text on designing shading devices begins with a
historical overview of indigenous responses to shading and ends by outlining a detailed analysis
and design process. Photographs of many different shading devices are used to support the
authors' claims.
Robbins, Claude L., Daylighting: Design and Analysis, Van Nostrand Reinhold Company, New
York, 1986. This is a technical two-part handbook that explores the fundamentals of daylighting.
The first part presents the principal sources, control devices, and analysis methods used in
daylighting. The second part contains reference material needed to supplement the design
methodologies given.
Villecco, M., Selkowitz, S., and Griffith, J. W., Strategies of Daylight Design, AIA Journal,
September 1979, pp. 68-77, 104, 108, 110, 112. This is a comprehensive article on daylighting
design. The article is a good introduction to principles and concepts due to its scope and
accuracy. Emphasis is on the qualitative aspects of design instead of the quantitative.
LINKS
International Commission of Illumination (http://www.ping.at/cie) : United States National
Committee CIE/(USA) is a not-for-profit organization formed in 1913 to assist the International
Commission on Illumination in achieving its objectives in the fields of light and lighting.
Illuminating Engineering Society of North America (http://www.iesna.org): Organization
whose mission is to advance knowledge and disseminate information for the improvement of the
lighted environment for the benefit of society.
Lawrence Berkeley Laboratory (http://www.lbl.gov): Research laboratory operated by the
University of California as part of the U.S. Department of Energy's national laboratory system.
Inter.Light (http://www.light-link.com): Internet source for lighting specifiers.
Lighting Research Center, School of Architecture, Rensselaer Polytechnic Institute
(http://www.lrc.rpi.edu): The world's largest university-based research and educational
institution dedicated to lighting. The LRC takes a unique and energetic approach to problem
solving with a commitment to bringing together unparalleled resources for lighting research.
Magnetek (http://www.magnetek.com): Electrical equipment manufacturer. Product line
includes lighting ballasts.
Lutron (http://www.lutron.com): Offers dimmers, home automation and energy management
systems for fluorescent lighting.
Southwall Technologies (http://www.southwall.com): Southwall designs and produces thin
film coatings that selectively absorb, reflect or transmit certain types of electromagnetic radiation.
U.S. EPA Green Lights Program (http://www.epa.gov/greenlights.html): Green Lights is an
innovative, voluntary pollution prevention program.