James
R. Benya, PE
Benya Lighting Design
December 2001
ighting
is and always has been an important factor in designing and operating
schools. Until the 1950s, natural light predominated as a means of illuminating
most school spaces. Classroom design was based in large part on time-honored
relationships between window sizes and room dimensions. As electric power
costs declined and designers began to take advantage of the increased
flexibility provided by electric lighting, daylighting took a secondary
role. Now, highly energy efficient windows and skylights and a renewed
recognition of the positive psychological and physiological effects of
daylighting (Heschong Mahone Group) allow a healthy and economical mix
of natural and electric illumination in new and renovated schools.
Simply adding windows or skylights to a classroom is not necessarily responsible
daylighting. Poorly designed daylighting, as with poorly designed
electric lighting, can create visual discomfort and disabling glare. Incorrectly
placed daylighting can introduce undesirable solar heat gain, causing
discomfort and increasing ventilation and air conditioning loads and energy
use.
Good daylighting design requires understanding a building's local climate
and use patterns and the location, placement, and shading of windows and
skylights relative to their solar orientation. A good daylighting system
provides:
• balanced, diffuse, glare-free daylight from two or more directions;
• sufficient light levels for the tasks in the space;
• operable shading devices to reduce light intensity for audio-visual programs and computer work;
• windows for interest, relaxation, and communication with the outdoors; and,
• exterior shading devices as needed to minimize solar heat gains during the cooling season.
The concept of cool daylighting is
a systematic approach to daylighting design that ensures that the daylight
is controlled through a combination of glazing systems (such as low-e),
shading systems, and architectural design. The result is a building that
uses significantly less energy than an ordinary school by simultaneously
reducing electric lighting and cooling loads. However, to be effective,
daylighting must be supplemented by automatically controlled electric
lighting that dims in response to daylight levels.
There is a side benefit to daylighting: by turning off the electric lights
when they are not needed, the life of the electric lighting system is
extended and maintenance costs are reduced. A simple automatic photo-control
system can switch off one, two, or three fluorescent lamps per light fixture,
depending upon the amount of daylight present. By reducing the use of
the electric lights by 50 percent, their life span will be doubled and
associated maintenance costs cut in half.
Daylighting can be effective and energy efficient for almost all school
spaces, including classrooms, cafeterias, offices, shops, gyms, pools,
corridors, locker rooms, and study halls. Some daylighting approaches,
especially top lighting (skylights), can be added to existing buildings.
For instance, many gyms could easily employ simple, reliable commercial
skylights that would allow lights to be turned off during much or all
of the day. This saves energy and reduces the cost of maintaining the
electric lighting system, a significant expense.
Although daylighting design for classrooms can be as simple as installing
good windows, the best designs often employ clerestories and other more
complex lighting devices such as light shelves. Remember, windows that
provide a view can also introduce glare. Windows also introduce side light,
which usually is not as good as top light for illuminating tasks.
In summary, daylighting is beneficial to student learning in addition
to simply being pleasant. Employed correctly, daylighting can dramatically
cut electric lighting, energy, and maintenance costs, even in cloudy or
northern latitudes. The resultant energy savings can, in the long term,
offset the increased costs of adding daylighting while increasing comfort
and student performance.
Even if the school is well daylighted, an electric lighting system is
needed for inclement days, early and late winter hours, and evening classes.
The challenge is to provide a lighting system that is energy efficient,
has a long life, and requires minimal maintenance.
Lamp technology. For the greatest energy efficiency and best color
rendering, school lighting should employ either fluorescent T-8 or T-5
linear lamp technology with electronic ballasts. The latest T-8 lamps,
called second generation, produce more than 10 percent more light per
watt than the original T-8 lamps and 50 percent more light per watt than
the old T-12 lamps (still the most commonly used lamps in older schools).
The second-generation T-8 lamps are currently about 30 percent more expensive
than ordinary T-8 lamps, but their superior color and light output are
worth the cost and they last about 20 percent longer. In a typical classroom,
the added cost of purchasing second-generation lamps (as compared to T-8
generic lamps) is about $5 per year. However, if the additional light
from the lamps is utilized through good design practice, the classroom
will use about 200 fewer watts and will save about $50 per year in energy
costs. T-8 lamps can be easily retrofitted into existing lighting systems.
T-5 linear lighting systems are best suited to new schools or schools
undergoing major remodeling. They are most effective when used for suspended
uplighting, direct-indirect pendant lighting, cove lighting, under- cabinet
lighting, or in specialized applications. Because the T-5 lamp and ballast
system is more expensive than the T-8 system, the two systems should be
compared to determine which best meets a school's needs. The T-5 HO (high
output) lighting system is rapidly gaining prominence as the preferred
lighting system for gymnasiums, pools, and other spaces with high ceilings.
Compact fluorescent lamps should replace incandescent lamps in downlights,
wall bracket lights, and utility lights. Because of improvements in low
temperature performance, compact fluorescent lamps also may be used for
some exterior lighting applications such as canopy downlights, utility
wallpacks and some types of security lighting.
High intensity discharge (HID) lamps should be used primarily outdoors
(in parking lots, athletic fields, and high-wattage exterior lights) and
for a few interior applications. Metal halide lamps are strongly recommended
(as opposed to high-pressure sodium) for their good color rendering and
white light, which provides better night vision. Until recently, HID lamps
were used in gyms, pools, and other spaces with high ceilings. With the
advent of T-5 HO and multiple compact fluorescent lamps, however, indoor
applications for HID lamps should be chosen carefully and only after weighing
a fluorescent alternative. The reason is simple: fluorescent systems generate
more light per watt and provide superior color. The exception is high
color-rendering ceramic metal halide lamps. These new lamps are not nearly
as energy efficient as fluorescent lamps, but they are the most efficient
source for display lighting and a few other specialty applications where
color rendering is important.
There are very few applications for traditional tungsten sources of any
kind. The short lamp life and low energy efficiency of tungsten lamps
make them a poor choice. They should only be used in theaters, art galleries,
and in spaces where dimming is important, such as multipurpose rooms.
The latest halogen IR (infrared) lamps should be specified, for they produce
light about 33 percent more efficiently than ordinary incandescent lamps.
On the horizon, new light sources such as light-emitting diodes (LEDs)
and induction lamps may ultimately change the way we approach lighting.
The only current practical application of LED technology, however, is
for exit and directional signs, and induction lamps are cost effective
only when used in places that are difficult and costly to maintain (induction
lamp life is generally five times longer than the best fluorescent lamps).
A few other sources might be considered for special applications, such
as cold cathode lighting, neon, and fiber optics, but, if used extensively,
these sources will generally prove to be costly and comparatively inefficient.
Lighting fixtures (luminaires). Much of the lighting equipment
used in schools is, and should be, commercial grade, similar to the equipment
used in offices, stores, and other kinds of commercial buildings. When
choosing lighting systems and fixtures, think about efficiency, glare
control, durability, cost, and maintainability, for which there are many
cost-effective choices. New lighting trends to consider:
• Suspended indirect luminaires are recommended in classrooms. Suspended indirect luminaires with relatively low-cost sheet metal bodies have become reasonably competitive with recessed troffer lighting. Indirect lighting provides a superior quality of light by illuminating the ceiling, which redirects light downward uniformly and without glare. However, to use these lighting systems, ceiling heights should be at least 9 feet 6 inches, and walls and ceilings should be a light color.
• Direct-indirect luminaires, which are more efficient than indirect luminaires alone, work well in classrooms. They are slightly more expensive to install, but high performance direct-indirect lighting expends about 20 percent less energy for the same light levels as indirect lighting alone. A ceiling of at least 9 feet is needed, and walls and ceilings should be a light color.
• T-5 HO systems with specially designed reflectors are the most efficient and economical systems for use in gyms and other spaces having high ceilings. These systems permit multiple-level switching and other control options that do not work with traditional HID lighting systems. Multiple compact fluorescent lamp luminaires and metal halide industrial luminaires also may be used, depending on ceiling heights and other factors.
• Fluorescent and compact fluorescent vandal-resistant luminaires are available in architectural styles that look pleasing, even when the school is built to withstand rough service.
• Several other efficient fixtures are available, such as the recessed indirect troffer that works well for corridors and other spaces.
By following the six steps below, it is possible to design lighting systems
that use half the energy conventional designs used just a few years ago:
1. Use daylighting strategies throughout the school. Design the
electric lighting so that lights can be adjusted in response to changes
in daylight levels.
2. Select the best light source suitable for the application. Considering
the excellent color quality available from modern fluorescent and compact
fluorescent lamps, there is rarely a need to compromise. In a few cases,
however, a good design might use a small amount of tungsten lighting or
HID lamps. Carefully weigh all options before choosing.
3. Use the most efficient luminaires. For instance, modern direct-indirect
luminaires are 85 to 90 percent efficient, as compared to the 60 to 70
percent efficiency of older styles. Many of today's luminaires are open
bottomed, which minimizes dirt accumulation and assures good lighting
performance even when maintenance is reduced.
4. Use luminaires that produce a good coefficient of utilization (CU).
The CU takes into account the way a luminaire works within a particular
space. This is especially important with indirect lighting systems, which
have an excellent CU in a room with a flat ceiling 10 feet above the floor
but have a reduced CU at higher ceiling heights.
5. Design using the latest recommendations of the Illuminating Engineering
Society of North America (IESNA). The IESNA Lighting Handbook, 9th
Edition, contains new recommendations for lighting levels (footcandles
or lux). These levels and their applications can result in lower energy
use when properly applied. See also IESNA's Recommended Practice for
Lighting for Educational Facilities (IESNA).
6. Use modern lighting controls throughout the school. With electronic
dimming ballasts, fluorescent dimming is quiet, flicker-free, and energy
efficient. Automatic fluorescent dimming can be employed in every room
with adequate daylighting, although this option is more expensive. Other
types of modern lighting controls, including motion sensors and energy
management systems, should be used to reduce operating time. Remember,
the amount of money spent on energy is the power (kilowatts) of the system
multiplied by the time it is operating (hours) and the price of electricity.
Modern lighting controls save money by reducing the time that lights are
used unnecessarily.
A high performance school should have a maximum lighting power usage for
interior lighting of less than 1.2 watts per square foot. When combined
with effective lighting controls, the total energy use of a high performance
school is much lower than in ordinary schools. And when daylighting is
used properly, schools can operate with very little lighting power under
most peak conditions.
Q: I have heard that full spectrum lighting is good for use in
schools. Is this true?
A: Thirty years ago, the most common fluorescent lamps were cool
white, which is a color of white light having a distinct bluish tint.
People hated them. The idea of full spectrum lighting began in the 1970s
as a sales tactic to promote particular brands of fluorescent lamps. Those
specific lamps generate a bluish white light similar to natural daylight.
Although the color of the lamp was significantly better than cool white,
the manufacturers made claims about the lamps' health benefits. Many schools
installed them as a result. The Food and Drug Administration ruled in
1985 that these full spectrum lamps provided no health benefits.
Modern T-8 versions of these lamps are available and provide a bluish
light of high color quality. Consider using these 5000 K color-rated lamps
for art studios because the color balance is better tuned for fine color
discrimination. For most school lighting, however, lamps with a color
rating of 3500 K or 4100 K tend to be preferred for economy and ease of
obtaining replacements.
Q: We live in the northern portion of the United States where
natural light can be limited during the winter months. Should special
lighting for treating seasonal affective disorder (SAD) be installed in
our schools?
A: SAD is a medical condition that requires a professionally managed
program of lighting and medication. Contrary to popular belief, ordinary
office and school lighting systems cannot be used to counter the effects
of SAD. Proper treatment involves special lighting systems, and the lighting
must be introduced in a clinical manner. However, the use of daylighting
provides natural changes in illumination levels that are thought to be
psychologically beneficial.
Q: The security lights at our neighborhood school are on motion
sensors and are not activated unless someone is near the school. Is this
safe?
A: The concept of the black-out school is based on the assumption
that vandals will not be attracted to a blacked out building, especially
when sensors activate lights to announce their presence. As long as the
motion sensors are properly designed and avoid detecting small animals,
this type of lighting approach is really quite clever. It saves energy,
helps reduce light pollution, and permits the use of low-cost halogen
floodlights instead of the more expensive HID or fluorescent lighting
systems. It is not suitable, however, for a school's parking lot or other
exterior lighting if the school has many evening events.
The table, "Lighting Sources for School Uses" is a guide for choosing electric lighting systems
for school applications. Note that mean lumens per watt is the
measure of the energy efficiency of the lamp system, much the way miles
per gallon measures the energy efficiency of an automobile. And a luminaire
is the proper term for a lighting fixture.
____________________
Light Source System: Fluorescent T-5
linear with programmed start electronic ballasts (24-, 36-, 48-, and 60-inch
lengths)
Mean Lumens per Watt: 91
Luminaires: Specialty lighting, such as under-cabinet, suspended
indirect, wallwashing
Types of Spaces in a School: Classrooms, offices, multipurpose
rooms, libraries
____________________
Light Source System: Fluorescent T-8
second- generation linear with electronic instant start ballasts or programmed
start ballasts (24-, 36-, 48-, and 60-inch lengths)
Mean Lumens per Watt: 92
Luminaires: General lighting in troffers, suspended lighting systems,
wraparounds, strips
Types of Spaces in a School: Classrooms, offices, multi- purpose
rooms, lockers, toilets, stairs, libraries, utility areas, hallways, corridors,
labs, music rooms, shops, studios
____________________
Light Source System: Fluorescent T-5
HO linear with programmed start electronic ballasts (24-, 36-, 48-, and
60-inch lengths)
Mean Lumens per Watt: 81
Luminaires: Specialty lighting applications where high lumen output
is needed
Types of Spaces in a School: Gyms, pools, libraries, offices, multipurpose
rooms
____________________
Light Source System: Compact fluorescent
triple tube lamps (18, 26, 32, and 42 watts) with electronic ballasts
Mean Lumens per Watt: 50—72
Luminaires: Downlights, sconces, wallwashers, utility lights, wall
brackets, table and task lamps
Types of Spaces in a School: Lobbies, offices, multipurpose rooms,
toilets, halls and corridors, utility spaces, exterior canopies, walls,
bollards, utility applications
____________________
Light Source System: Pulse start metal
halide lamps (250 watts or higher)
Mean Lumens per Watt: 55—78
Luminaires: Industrial style downlights, parking lot lights, roadway
lights, large wallwashers, specialized uplights, floodlights, sports lights
Types of Spaces in a School: High-ceiling interior spaces (some
gyms, pools), park- ing lots, sports fields, other pole-mounted exterior
lighting
____________________
Light Source System: Pulse start ceramic
metal halide lamps (150 watts or lower), with electronic ballasts
Mean Lumens per Watt: 35—65
Luminaires: Track and recessed display lighting
Types of Spaces in a School: Feature displays
____________________
Light Source System: Halogen IR lamps
(60 to 100 watt PAR-38, 50 watt PAR-30) or low voltage halogen IR lamps
(37 watt MR16)
Mean Lumens per Watt: 20—30
Luminaires: Track and recessed display lighting, surface and recessed
downlighting
Types of Spaces in a School: Feature displays and house lighting
for theaters, performance spaces, and multipurpose rooms
____________________
Heschong Mahone Group. 1999. Daylighting in Schools: An Investigation
Into the Relationship Between Daylighting and Human Performance. San Francisco,
Calif.: Pacific Gas and Electric Company. Heschong Mahone Group
Illuminating Engineering Society of North America (IESNA). 2000. Lighting
Handbook, 9th Edition. New York: IESNA.
________________. 2000. Recommended Practice for Lighting for Educational
Facilities. New York: IESNA.
See the NCEF resource lists Daylighting and Lighting at http://www.edfacilities.org/rl/
The author especially thanks Barbara Erwine for her significant additions
to the text on daylighting.
James Ansley, Charles Eley, Barbara Erwine, Lisa L. Heschong, Randy Karels,
Henry Sanoff, Thomas M. Tolen, and Terry Whitney.
This publication was produced by the National Clearinghouse for Educational
Facilities (NCEF), an affiliate clearinghouse of the Educational Resources
Information Center (ERIC) of the U.S. Department of Education.