|
Electric Lighting
Lighting accounts for 31%
of the energy use in commercial buildings. Significant
reductions in energy use can be achieved by installing
energy-efficient lights, fixtures, and controls. In recent
years, new technologies such as electronic ballasts, dimmable
fluorescents, and others have revolutionized the lighting
industry. Retrofits to install new technologies are often cost
effective, paying back within a few years.
Compact
fluorescent light bulbs can replace incandescent light bulbs in
most commercial applications, and they are now widely available.
To demonstrate the high efficiency of these light bulbs, compare
the light output of a 60-watt incandescent bulb, at 775 lumens,
to the light output of a 32-watt T-8 compact fluorescent bulb,
at 3,050 lumens. That is roughly four times the light at half
the energy use.
Other options
available for commercial buildings include improved reflectors
for standard fluorescent fixtures, allowing the number of bulbs
per fixture to be reduced, and electronic ballasts, which can
save up to 25% of energy use compared to older magnetic
ballasts.
Energy Efficient Lighting
The quantity and quality of light around us determine how well
we see, work, and play. Light affects our health, safety,
morale, comfort, and productivity.
Lighting also directly affects our economy. As a nation, we
spend about one-quarter of our electricity budget on lighting,
or more than $37 billion annually. Yet much of this expense is
unnecessary. Technologies developed during the past 10 years can
help us cut lighting costs 30% to 60% while enhancing lighting
quality and reducing environmental impacts.
This publication is an introduction to lighting technology and
discusses how you can save energy while maintaining good light
quality and quantity. Specifically, you will learn about:
Lighting principles and definitions
Types of lighting and how each works
Energy-efficient lighting options, including day lighting, for
new or retrofit applications.
Lighting Principles and Terms
To choose the best lighting options, you should understand basic
lighting terms. This section explains terminology used in the
industry, which will help you better understand the potentially
confusing language you could hear in a lighting store.
Illumination
A lumen is a measurement of light output from a lamp,
often called a tube or a bulb. All lamps are rated in lumens.
For example, a 100-watt incandescent lamp produces about 1750
lumens.
The distribution of light on a horizontal surface is called its
illumination. Illumination is measured in foot-candles. A
foot-candle of illumination is a lumen of light distributed over
a 1-square-foot (0.09-square-meter) area.
The amount of illumination required varies according to the
difficulty of a visual task. Ideal illumination is the minimum
foot-candles necessary to allow you to perform a task
comfortably and proficiently without eyestrain. The Illuminating
Engineering Society says that illumination of 30 to 50
foot-candles is adequate for most home and office work.
Difficult and lengthy visual tasks�like sewing for extended
periods of time�require 200 to 500 foot-candles. Where no seeing
tasks (i.e., tasks whose speed and accuracy of completion are
affected by quality and quantity of light) are performed,
lighting systems need to provide only security, safety, or
visual comfort�requiring from 5 to 20 foot-candles of
illumination.
Another lighting term you will hear is efficacy. This is
the ratio of light output from a lamp to the electric power it
consumes and is measured in lumens per watt (LPW).
Lighting Uses
Experts divide lighting uses into three categories: ambient,
task, and accent lighting. Ambient lighting provides security
and safety, as well as general illumination for performing daily
activities. The goal of task lighting is to provide enough
illumination so that tasks can be completed accurately but not
provide so much light that entire areas are illuminated. Accent
lighting illuminates walls so they blend more closely with
naturally bright areas like ceilings and windows.
Light Quality
Light quality describes how well people in a lighted space can
see to do visual tasks and how visually comfortable they feel in
that space. Light quality is important to energy efficiency
because spaces with higher quality lighting need less
illumination. High-quality lighting is fairly uniform in
brightness and has no glare.
For example, direct intense sunlight streaming through the
windows of a room with chocolate brown carpets and dark wall
paneling will likely give too much contrast in brightness. The
pupils of your eyes will constantly adjust to the differing
bright nesses. Making this area visually comfortable would
involve using lots of artificial lighting with a high
illumination level.
On the other hand, in a pale-colored room bathed in soft light,
you can hardly tell where the light is coming from because no
one area of the room appears much brighter than another. The
walls, ceiling, floor, and work surfaces are relatively the same
light hue. People can perform tasks faster and with fewer
mistakes with this type of high-quality lighting. Also, lighting
such a room requires far less artificial lighting than the
previous example.
Glare
Eliminating glare (i.e., excessive brightness from a direct
light source) is essential to achieving good lighting quality.
Types of glare include direct glare, reflected glare, and
veiling reflections.
Direct glare results from strong light from windows or bright
lamps shining directly into your eyes. Reflected glare is caused
by strong light from windows or lamps that are reflected off a
shiny surface into your eyes. Veiling reflection is a special
type of reflected glare that can obscure contrasts and reduce
task clarity. Veiling reflections occur when light is reflected
into your eyes from a work surface, such as a printed page or a
computer screen.
Light Color and Color Rendering
Lamps are assigned a color temperature (according to the Kelvin
temperature scale) based on their "coolness" or "warmness." The
human eye perceives colors as cool if they are at the blue-green
end of the color spectrum, and warm if they are at the red end
of the spectrum.
Cool light is preferred for visual tasks because it produces
higher contrast than warm light. Contrast is the brightness
difference between different parts of the visual field, which is
the expanse of space you can see at a given instant without
moving your eyes. Warm light is preferred for living spaces
because it is more flattering to skin tones and clothing.
Keep in mind, though, that artificial light sources vary widely
in their color rendering indexes (CRI). The CRI is a measurement
of a light source's ability to render colors the same as
sunlight does. For example, incandescent lamps are rated at a
CRI of 100�nearly equal to sunlight�while some high-pressure
sodium lamps have a CRI of 22, which means they render colors
very poorly.
However, a light's color-rendering ability is not related to
whether it is a cool or warm color. For example, blue light from
the northern sky, white light at noon, and red light from a
sunset all have perfect color rendering (a CRI of 100) because
our eyes are designed to read the colors of objects illuminated
by sunlight.
Types of Lighting
There are four basic types of lighting: incandescent,
fluorescent, high-intensity discharge, and
low-pressure sodium.
Incandescent lighting is the most common type of lighting used
in residences. Fluorescent lighting is used primarily in
commercial indoor lighting systems, while high-intensity
discharge lighting is used only for outdoor lighting
applications. Low-pressure sodium lighting is used where color
rendering is not important, such as highway and security
lighting. These lighting types vary widely in their
construction, efficiency, color characteristics, and lamp life.
Incandescent
Incandescent lamps are the least expensive to buy but the most
expensive to operate. Incandescent light is produced by a tiny
coil of tungsten wire that glows when it is heated by an
electrical current.
Incandescent lamps have the shortest lives of the common
lighting types. They are also relatively inefficient compared
with other lighting types. However, significant energy and cost
savings are possible if you select the right incandescent lamp
for the right job. The three most common types of incandescent
lights are standard incandescent, tungsten halogen, and
reflector lamps.
Standard incandescent
Known as the "A-type light bulb," these lamps is the most common
yet the most inefficient light source available. Larger wattage
bulbs have a higher efficacy than smaller wattage bulbs. Note
that a larger wattage lamp or bulb may not be the most energy-
or cost-effective option, depending on how much light is needed.
"Long- life" bulbs, with thicker filaments, are a variation of
these A-type bulbs. Although long-life bulbs last longer than
their regular counterparts, they are less energy efficient.
Tungsten halogen
this newer type of incandescent lighting achieves better energy
efficiency than the standard A-type bulb. It has a gas filling
and an inner coating that reflect heat. Together, the filling
and coating recycle heat to keep the filament hot with less
electricity. These lamps are considerably more expensive than
standard incandescent and are primarily used in commercial
applications: theater, store, and outdoor lighting systems.
Reflector lamps
Reflector lamps (Type R) are designed to spread light over
specific areas. They are used mainly indoors for stage/theater
and store applications, as well as floodlighting, spotlighting,
and down lighting.
Parabolic aluminized reflectors (Type PAR) are used for outdoor
floodlighting. The ellipsoidal reflector (Type ER) focuses the
light beam about 2 inches (5 centimeters) in front of its
enclosure and is designed to project light down from recessed
fixtures. Ellipsoidal reflectors are twice as energy efficient
as parabolic reflectors for recessed fixtures.
Fluorescent
The light produced by a fluorescent tube is caused by an
electric current conducted through mercury and inert gases.
Fluorescent lighting is used mainly indoors�both for ambient and
task lighting�and is about 3 to 4 times as efficient as
incandescent lighting. Fluorescent lamps last about 10 times
longer than incandescent. But, to gain the most efficiency, you
should install fluorescents in places where they will be on for
several hours at a time.
Fluorescent lights need ballasts (i.e., devices that control the
electricity used by the unit) for starting and circuit
protection. Ballasts consume energy. You can increase the energy
savings for existing fluorescent lighting by relamping (e.g.,
replacing an existing lamp with one of a lower wattage),
replacing ballasts, and replacing fixtures with more efficient
models.
Tube fluorescent
these lamps are the next most popular lamps after A-type
incandescent lamps. The two most common types are 40-watt,
4-foot (1.2-meter) lamps and 75-watt, 8-foot (2.4-meter) lamps.
Tubular fluorescent fixtures and lamps are preferred for ambient
lighting in large indoor areas because their low brightness
creates less direct glare than do incandescent bulbs.
Compact fluorescent
Compact fluorescent lamps (CFLs) are the most significant
lighting advance developed for homes in recent years. They
combine the efficiency of fluorescent lighting with the
convenience and popularity of incandescent fixtures. CFLs can
replace incandescent that are roughly 3 to 4 times their
wattage, saving up to 75% of the initial lighting energy.
Although CFLs cost from 10 to 20 times more than comparable
incandescent bulbs, they last 10 to 15 times as long. This
energy savings and superior longevity make
CFLs are one of the best energy efficiency investments
available.
When introduced in the early- to mid-1980s, CFLs were bulky,
heavy, and too big for many incandescent fixtures. However,
newer models with lighter electronic ballasts are only slightly
larger than the incandescent lamps they replace.
CFLs come in integral and modular designs.
Integral CFLs have ballast and a lamp in a single disposable
unit. Modular designs
feature separate ballast that serves about five lamp
replacements before it wears out.
High-Intensity Discharge
High-intensity discharge (HID) lamps provide the highest
efficacy and longest service life of any lighting type. They are
commonly used for outdoor lighting and in large indoor arenas.
HID lamps use an electric arc to produce intense light. They
also require ballasts, and they take a few seconds to produce
light when first turned on because the ballast needs time to
establish the electric arc.
The three most common types of HID lamps are mercury vapor,
metal halide, and high-pressure sodium. HID lamps
and fixtures can save 75% to 90% of lighting energy when they
replace incandescent lamps and fixtures. Significant energy
savings are also possible by replacing old mercury vapor lamps
with newer metal halide or high-pressure sodium lamps.
Mercury vapor�the
oldest type of HID lighting�is used primarily for street
lighting. Mercury vapor lamps provide about 50 lumens per watt.
They cast a very cool blue/green white light. Most indoor
mercury vapor lighting in arenas and gymnasiums has been
replaced by metal halide lighting, which has better color
rendering and efficiency.
Metal halide
lamps are similar in construction and appearance to mercury
vapor lamps. The addition of metal halide gases to mercury gas
within the lamp results in higher light output, more lumens per
watt, and better color rendition than from mercury gas alone.
Metal halide lamps are used to light large indoor areas such as
gymnasiums and sports arenas, and for outdoor areas such as car
lots or anywhere that color rendition is important.
High-pressure sodium
lighting is becoming the most common type of outdoor lighting.
It provides 90 to 150 lumens per watt�an efficiency exceeded
only by low-pressure sodium lighting. High-pressure sodium lamps
are also reliable and have long service lives. Their color is a
warm white, and their color rendition ranges from poor to fairly
good depending on design and intended use.
Low-Pressure Sodium
Low-pressure sodium lamps work somewhat like fluorescent lamps.
They are the most efficient artificial lighting, have the
longest service life, and maintain their light output better
than any other lamp type. Low-pressure sodium lighting is used
where color is not important because it renders all colors as
tones of yellow or gray. Typical applications include highway
and security lighting.
Energy Efficiency with Lighting
Lighting accounts for 20% to 25% of all electricity consumed in
the United States. An average household dedicates 5% to 10% of
its energy budget to lighting, while commercial establishments
consume 20% to 30% of their total energy just for lighting.
In a typical residential or commercial lighting installation,
50% or more of the energy is wasted by obsolete equipment,
inadequate maintenance, or inefficient use.
Saving lighting energy requires either reducing electricity
consumed by the light source or reducing the length of time the
light source is on. This can be accomplished by:
Lowering wattage, which involves replacing lamps or entire
fixtures
reducing the light source's on-time, which means improving
lighting controls and educating users to turn off unneeded
lights
using day lighting, which reduces energy consumption by
replacing electric lights with natural light
performing simple maintenance, which preserves illumination
and light quality and allows lower initial illumination levels.
Replacing Lamps and Fixtures
"Relamping" means substituting one lamp for another to save
energy. You can decide to make illumination higher or lower when
relamping. But be sure that the new lamp's lumen output fits the
tasks performed in the space and conforms to the fixture's
specifications.
When relamping an entire store or office, first test the new
lamps in a small area to ensure adequate illumination, occupant
satisfaction, and compatibility of the new lamp and the old
fixture.
Matching replacement lamps to existing fixtures and ballasts can
be tricky, especially with older fixtures. Buying new fixtures
made for new lamps produces superior energy savings,
reliability, and longevity compared with relamping.
Relamping incandescent fixtures
Much has been learned about fixture design since the energy
crises of the 1970s. Many indoor fixtures trap a significant
portion of light inside the fixture, while many outdoor fixtures
tend to disperse much of their light beyond the intended area,
which causes light pollution.
New incandescent fixtures are designed to push all their light
out into the room. Others use smaller tungsten halogen lamps.
Advances in indoor fixture design include brighter reflectors
and better reflecting geometry.
Many incandescent lamps are mismatched to their tasks. Some have
excessive wattages and therefore create unnecessarily high
illumination. This can be corrected by using lamps with smaller
wattage.
Some existing incandescent lamps may not be the best type of
lamp for their application. A-type light bulbs can often be
replaced with improved lamp designs, such as reflectors or
tungsten halogen lamps. And, for energy savings of 60% to 75%,
many incandescent lamps can be replaced by CFLs.
When used in recessed fixtures, standard A-type lamps and
reflector lamps waste energy because their light gets trapped.
To save energy, you could replace a 150-watt standard reflector
with a 75-watt ellipsoidal reflector (ER). Remember, though,
that ER lamps are less efficient at delivering light from
shallow fixtures, so use reflectors or parabolic reflectors for
these purposes.
You can also replace standard A-type lamps with CFLs in spaces
where lights are needed for long periods of time. A standard
18-watt CFL replaces a 75-watt A-type lamp. CFLs are also
packaged in the same glass reflector lamps as incandescent
lamps. Use CFLs packaged as ellipsoidal reflectors (type-ER) in
recessed fixtures. Use reflector (R) or parabolic reflector
(PAR) CFLs for flood and spotlighting. New CFL fixtures have
built-in electronic ballasts and polished metal reflectors.
Relamping fluorescent fixtures
Although fluorescent lamps are generally energy efficient, there
are new, even more efficient lamps that use better electrodes
and coatings than do older fluorescent lamps. They produce about
the same lumen output with substantially lower wattage.
Common 40-watt and 75-watt lamps can be replaced with
energy-saving lamps of 34 watts and 60 watts, respectively.
Energy-saving lamps for less-common fluorescent fixtures are
also available.
If you need to replace the ballasts in your fluorescent
fixtures, consider using one of the improved varieties. These
fluorescent ballasts, called improved electromagnetic ballasts
and electronic ballasts, raise the efficiency of the fixture 12%
to 30%.
The new electromagnetic ballasts reduce ballast losses, fixture
temperature, and system wattage. Because they operate at cooler
temperatures, they last longer than standard electromagnetic
ballasts.
Electronic ballasts operate at a very high frequency that
eliminates flickering and noise. They are even more efficient
than improved electromagnetic ballasts. Some electronic ballast
even allows you to operate the fluorescent lamp on a dimmer
switch, which usually is not recommended with most fluorescents.
Improving Lighting Controls
Lighting controls are devices for turning lights on and off or
for dimming them. The simplest type is a standard snap switch.
Other controls are photocells, timers, occupancy sensors, and
dimmers.
Snap switches, located in numerous convenient areas, make it
easier for people in large, shared spaces to turn off lights in
unused areas.
Photocells turn lights on and off in response to natural light
levels. Photo-cells switch outdoor lights on at dusk and off at
dawn, for example. Advanced designs
gradually raise and lower fluorescent light levels with changing
daylight levels.
Mechanical or electronic time clocks automatically turn on and
off indoor or outdoor lights for security, safety, and tasks
such as janitorial work.
Crank timers, which are spring-driven and similar to old oven
timers, limit lights to short durations where the need for light
is brief.
Occupancy sensors activate lights when a person is in the area
and then turn off the lights after the person has left. They are
popular for areas used infrequently, such as warehouses. They
also offer security advantages over continuous lighting: when
lights suddenly come on, they startle intruders and alert
residents and neighbors to motion in the area.
Dimmers reduce the wattage and output of incandescent and
fluorescent lamps. Dimmers also increase the service life of
incandescent lamps significantly. However, dimming incandescent
lamps reduces their lumen output more than their wattage. This
makes incandescent lamps less efficient as they are dimmed.
Dimming fluorescents requires special dimming ballasts and lamp
holders, but does not reduce their efficiency.
Fluorescent Lamp Disposal
All fluorescent lights contain small amounts of mercury, and
some compact fluorescent lamps with magnetic ballasts contain
small amounts of short-lived radioactive material. Because of
these hazardous materials, you should not toss burned-out lamps
into the trash. Find out if there is a recycling program for
them in your community�they are becoming more common�or dispose
of them with other household hazardous wastes such as batteries,
solvents, and paints at your community's designated drop-off
point or during a designated day when you can put such materials
with your curbside trash pickup.
Day lighting
Day lighting means using daylight for indoor lighting. Modern
buildings designed for day lighting typically use 40% to 60%
less electricity for lighting needs than do conventional
buildings.
Sunlight and daylight are free and readily accessible. However,
using sunlight without causing glare and without overheating a
building can be difficult. Glare can be avoided by using window
sills, walls, louvers, reflective blinds, and other devices to
reflect light deep into the building. Be careful to locate
windows and skylights away from the sun's direct rays to avoid
overheating. For example, placing skylights on the north slope
of your roof rather than on the southern exposure may reduce
heat transfer. In addition, look for windows with new selective
glazing that transmit the most visible light while excluding the
most solar heat.
For more information on day lighting and windows, contact the
Energy Efficiency and Renewable Energy Clearinghouse (EREC�see
Source List).
Lighting Maintenance
Maintenance is vital to lighting efficiency. Light levels
decrease over time because of aging lamps and dirt on fixtures,
lamps, and room surfaces. Together, these factors can reduce
total illumination by 50% or more, while lights continue drawing
full power. The following basic maintenance suggestions can help
prevent this.
clean fixtures, lamps, and lenses every 6 to 24 months by
wiping off the dust. However, never clean an incandescent bulb
while it is turned on. The water's cooling effect will shatter
the hot bulb.
Replace lenses if they appear yellow.
Clean or repaint small rooms every year and larger rooms every
2 to 3 years. Dirt collects on surfaces, which reduces the
amount of light they reflect.
Consider group relamping. Common lamps, especially
incandescent and fluorescent lamps lose 20% to 30% of their
light output over their service life. Many lighting experts
recommend replacing all the lamps in a lighting system at once.
This saves labor, keeps illumination high, and avoids stressing
any ballast with dying lamps.
Optimizing Energy Efficiency and Lighting
Quality
When making changes designed to increase the energy efficiency
of lighting, it often pays to redesign the building's entire
lighting system. This can improve lighting quality, make visual
tasks easier, and save 50% or more on energy costs.
Often, you can reduce light levels without reducing light
quality by following these procedures.
Redesign visual tasks. For example, use a better printer with
darker printing.
Reduce light levels where there are no visual tasks. Provide
the minimum light necessary for safety, security, and
aesthetics.
Reduce light levels for visual tasks where those levels are
currently excessive.
If you want to cut energy consumption from lighting while
enhancing light quality, consider the following.
Establish ambient illumination at minimum acceptable levels.
Provide task lighting at the optimal level depending on the
difficulty of visual tasks. For example, sewing requires more
light than cooking.
Increase the efficiency of lamps, ballasts, and fixtures.
Improve light quality by reducing glare and brightness
contrast.
Use day lighting where possible and practical.
Better Light, Less Cost
Using just a few of these ideas will help lower your electricity
costs from lighting and make your home or workplace more
comfortable and efficient.
NOTICE
This report was prepared as an account of work sponsored by an
agency of the United States government. Oksolar.com
|
