Energy Efficient Buildings
Energy Efficient Lighting
The electricity to power lights and electrical equipment is a significant fraction of total
building electricity. Moreover, heat gain from lighting, electrical equipment and people
are significant components of building heating and cooling loads. Thus, energy efficient
buildings utilize natural lighting and efficient electrical lighting and equipment to reduce
both primary and cooling energy use.
Residential Building Energy Breakdown
Commercial Building Energy Breakdown
Lighting Introduction
In the U.S., about 19% of all electricity is used for lighting (ACEEE, 2000). Typical lighting
power densities are about 1-2 W/ft2 in the commercial sector and 1-1.5 W/ft2 in the
manufacturing sector (UD-IAC, 2008).
Modern lighting systems are much more energy efficient that previous systems. Thus,
upgrading older lighting presents an opportunity for energy savings. However, an
effective lighting system must do more than deliver light efficiently. Effective lighting
must provide the right quantity of light, with good color rendition and minimal glare.
Quality lighting and day lighting has been shown to improve productivity and enhance
worker satisfaction. In most cases, small improvements in worker productivity greatly
outweigh lighting energy costs. Thus, when considering upgrades to reduce lighting
energy use and costs, it is essential that the changes maintain or improve the quality of
light.
End use lighting savings opportunities include:



Turn off blocked lights and lights in unoccupied areas.
Use motion sensors to turn off lights in seldom used areas such as warehouses.
Turn off unnecessary lights near windows or skylights.
1




Use photo sensors to turn on/off outdoor lights.
Determine required light level and disconnect lights in overlit areas.
Replace colored glass and fiberglass with corrugated polycarbonate, and turn off
unnecessary lights.
Add windows or skylights, and turn off unnecessary lights.
Lighting distribution system savings opportunities include:





Clean dirty lenses and replace yellowed lenses.
Add reflectors to fluorescent strip lights.
Add task lighting over critical areas and decrease general lighting.
Lower lights beneath scaffolding.
Paint ceilings and walls lighter color.
Lighting replacement savings opportunities include



Replace incandescent and halogen lights with compact fluorescent lights.
Replace T12 fluorescent lights with T8 or T5 lights and electronic ballasts.
Replace HID lights with HBF lights.
Productivity and Lighting
Several studies have documented productivity improvements due to lighting upgrades
and the increased use of sunlight for interior lighting. A few examples are listed here.
Lighting Upgrades
In the post office in Reno, Nevada, a lighting retrofit with a six-year payback increased
the number of letters sorted per hour by 6% and decreased the rate of sorting errors to
0.1% making the Reno Post Office the most efficient in the Western US. Energy savings
were about $22,400 per year, but the increase productivity was worth about $400,000
per year (Romm and Browning, 1999).
Boeing recently went through a lighting upgrade with a two-year payback. In addition
to energy savings, “the things that people tell us are almost mind boggling”, said one
manager. Machinists report being able to read calipers and tools more easily. The
improved contrast improves workers ability to detect imperfections in the shop by 20%.
This is important because “most of the errors… weren’t picked up until installation in
the airplane, where it is much more expensive to fix” (Romm and Browning, 1999).
Hyde Tools lighting upgrade reduced electricity costs by $48,000 per year. However,
“the quality of work improved significantly because we could see things we couldn’t see
before”. The manager estimates that the improved lighting results in about $250,000
per year in additional revenue (Romm and Browning, 1999).
2
Pennsylvania Power and Light saved $2,000 per year from their lighting upgrade, but the
time required to produce drawings decreased, saving them another $42,000 per year.
In addition, sick leave decreased from 72 to 54 hours per year. It was apparent that
“low quality seeing conditions were causing morale problems among employees”
(Romm and Browning, 1999).
West Bend Mutual Insurance Company’s move to a new building with advanced HVAC
and better lights reduced electricity costs from $2.16 /ft2 to 1.32 /ft2, and improved
productivity by 16.8% (Romm and Browning, 1999).
Day Lighting
The Herman Miller company built a new manufacturing plant with a large portion of its
lighting provided by skylights. Production output has consistently been over 20% higher
than in the previous electrically-lighted plant. Employees report that working conditions
are excellent (McDonough, 2008).
Lockheed Missiles and Space Company commissioned a new office building in California
in which the cost of extensive day lighting added an extra 4% to the buildings cost.
However, electricity costs will be reduced by about $500,000 per year for a four- year
payback. In addition, absenteeism dropped by 15%, which paid for 100% of the first
cost in the first year (Romm and Browning, 1999).
Skylights were installed on one half of the roof of a Wal-mart in Lawrence, Kansas. Sales
data indicated that the departments under the skylights sold more than the
departments under the electric lighting, and more than similar departments in other
stores. To test whether this was due to the skylights, the departments were switched
from one side of the store to the other. As before, sales from departments under the
sky lights increased (Romm and Browning, 1999).
A 1999 study conducted for Pacific Gas and Electric evaluated elementary student test
scores and found that, in classrooms with daylight, test scores improved by over 20+%.
Retail sales in a chain of 100+ similar stores were also evaluated. Sales were found to be
as much as 40% higher in stores with skylighting (Heschong Mahone Group, 1999).
Lighting Fundamentals
Effective, energy-efficient lighting systems provide the right quantity of light, with good
color rendition and minimal glare, while minimizing energy-use. Each of these concepts
is described briefly in the sections that follow.
Light Quantity
The quantity of visible light radiated by a light source is measured in lumens. The
theoretical upper limit for the conversion of energy to light is 683 lm/W. Natural
3
daylight has luminous efficacy of about 110 lm/W. Electric lighting ranges from about
10 to 100 lm/W.
Illuminance is the quantity of light divided by the area on which it is incident.
Illuminance can be measured by light meters. The common measure of illuminance in
U.S. units is footcandles. One footcandle is one lumen per square foot.
1 fc = 1 lm/ft2
The Illuminating Engineering Society of North America (IESNA) publishes recommended
lighting levels for various tasks and spaces. IESNA recommended lighting levels for
some common spaces are shown in the table below (IESNA Handbook, 9th Edition). In
general, recommended lighting levels increase as the size and contrast of the visual task
decrease. Thus, the recommended lighting level will be near the lower level of the
range shown in the table below when the size and/or contrast of the visual task is large,
and will be near the upper level of the range when the size and/or contrast of the visual
task is small. For example, 15 fc may be sufficient for warehouses with large bulk items,
but 25 fc may be needed for warehouses with hand-stocked items. Similarly, 30 fc may
be sufficient for general manufacturing, but 50 fc may be required for manufacturing
tasks requiring visual precision.
Space/Function
Offices and classrooms
Corridors
Restrooms
Dining rooms
Merchandise Display
Warehouse
Manufacturing
Inspection
Recommended Lighting Level (fc)
30-50
5-10
5
10
50
5-30
30-50
50-100
Light Quality
Our eyes evolved to see in natural sunlight; thus, we distinguish colors best in sunlight.
Light from electric lamps is generated at lower temperatures than sunlight and reduces
our ability to distinguish between colors. Color Rendering Index (CRI) describes the
effect of a light source on the color appearance of an object. CRI varies between 0 and
100. Approximate CRIs of various types of lighting are shown in the table below.
Light Type
Sunlight
Incandescent
T8 Fluorescent
CRI
100
99
75-85
4
Metal halide
T12 Fluorescent (cool
white)
High-pressure sodium
65
60
22
Some tasks, such as inspection and painting, clearly require high-quality light. In
addition, most people prefer to work and live in light that is as close to sunlight as
possible; thus the CRI of a light source should always be a consideration when selecting
lights. For example, most people report seeing better under fluorescent lights with a
CRI of 85 than under high-pressure sodium lights with a CRI of 22, even when the
illuminance under the high-pressure sodium lights is higher.
Light Color
The color of light is often characterized by temperature. Many people prefer “warm”
white light with a temperature of about 2,700 K. “Bright” white light is at about 5,000 K.
Glare
Glare is uncomfortably high illuminance. Glare can be problematic with large windows
with direct sunlight and with direct high-intensity artificial lighting. For this reason,
windows are often equipped with some type of shading and luminaries are often
designed to diffuse light.
Electric Lighting
Common types of electrical lighting fall into three categories: incandescent, fluorescent
and high-intensity discharge. Important characteristics of each category are described
below.
Incandescent Lights
Thomas Edison invented the incandescent light bulb and it remains essentially
unchanged today. Incandescent lights produce light by simple radiation from a heated
tungsten filament. The lighting efficiency is generally low since most of the energy is
released as infrared radiation rather than visible light. In recent years, halogen has been
added to the filament increasing the efficiency and light output by about 30% in
‘halogen lights’. Incandescent lights are inexpensive, require almost no warm-up time,
and the lighting output does not degrade significantly over time. However, because of
their inefficiency, they are being replaced by compact fluorescent lights that use about
30% as much energy and last about seven times longer.
Fluorescent Lights
Fluorescent lights work by energizing Ar, Ar-Ne or Kr gasses inside a tube. The gasses
produce UV radiation that is converted to visible light when it interacts with phosphor
coatings on the inside of the tube. Fluorescent lights have a higher lighting efficiency
5
than incandescent lights. They start quickly and lighting output degrades only
moderately over time.
Fluorescent lamps are labeled using “F” and “T” notion. The “F” notation refers to the
nominal wattage of the lamp. The “T” notation denotes the diameter in units of 1/8
inch. Thus, Thus ‘F32T8’ refers to a lamp with nominal power draw of 32 W and 1 inch
diameter. Over time, the progression has been toward thinner lamps, from T12 to T8 to
T5, with corresponding improvements in energy efficiency and color rendition. Tubular
fluorescent lamps with low mercury content are generally marked with green end caps.
All fluorescent lights require ballasts. The ballast regulates voltage and uses some
energy itself. Old-style T12 lamps used magnetic and electro-magnetic ballasts. T8 and
T5 lamps use electronic ballasts. New electronic ballasts are more energy-efficient,
eliminate the flicker associated with old-style magnetic ballasts, are quieter and contain
less heavy metals than old-style ballasts.
The actual power draw of the lamp, and the corresponding lamp output are determined
by the power supplied to the lamp by the ballasts. The relative power delivered by the
ballast to the lamps is called “ballast factor”. For example, lamps powered by a ballast
with a ballast factor of 0.87, will draw about 87% of their rated wattage and deliver
about 87% of their rated lighting output.
The fixture that houses the lamps and ballast and directs the light onto the work plane is
called a luminaire. The most common types of fluorescent luminaries are recessedtroffer and suspended luminaires. Many offices employ recessed-troffer luminaires.
The troffers are typically equipped with acrylic lenses or parabolic grids to diffuse the
light. Although acrylic lenses transmit more light than parabolic grids, parabolic grids
produce less glare and are therefore widely used in rooms with video displays.
Recessed parabolic and lensed troffers.
In industrial applications, fluorescent luminaires are typically suspended from the
ceiling. Simple “strip” lights without reflectors attached to the sides lose a significant
amount of the light sideways and upwards. Adding reflectors to the sides of the
luminaire pushes more light downward onto the work plane, and reduces the number of
lights required to generate a given lighting level on the work plane. The most efficient
fluorescent luminaires employ polished metal mirrors above each lamp to direct the
6
maximum possible light onto the work plane. High-bay fluorescent (HBF) luminaires
employ these polished reflectors, and are displacing HID lights in industrial applications
due to their improved energy efficiency, color rendition and other attributes.
A) fluorescent strip light, B) fluorescent strip light with side reflectors, C) high-bay
fluorescent light with individual polished mirror reflectors.
High-Intensity Discharge Lights
High-intensity discharge (HID) lights are primarily used in applications with high ceilings
or for outdoor lighting. The most common types of HID lights are metal halide (MH) and
high-pressure sodium (HPS). MH lights produce a white light with a CRI of about 65, and
have a lighting efficiency of about 70 lm/W. HPS lights have a lighting efficiency of
about 95 lm/W, but produce a yellow light with poor color rendering (CRI = 20); thus,
these lights are best suited for outdoor and warehouse applications.
All HID lamps require a ballast. The ballast for a typical 400-W HID lamp uses 50 to 65
W. HID lamps take about 3 minutes to start-up when cold and about 25 minutes when
warm. Thus, most HID lighting systems include a few fluorescent safety lights that start
up immediately in the advent of a power interruption. Two-stage and dimmable HID
ballasts with occupancy sensors are available, Two-stage HID ballasts typically have a
low-lighting stage that produces 35% of the light while using 50% of the rated energy.
Luminaries for HID lights typically use acrylic or spun-aluminum reflectors. Acrylic
reflectors spread about 10% of the light horizontally and toward the ceiling. Because of
this, they are often used in retail applications where bright ceilings are more visually
attractive. Spun aluminum reflectors are the most common type in industrial
applications and direct all light toward the floor. HID luminaries are classified as highbay for placements higher than about 25 feet, and low-bay for placements less than
about 25 feet. Low-bay luminaries have acrylic lenses that spread the light outward
over a wider surface area.
7
A)
acrylic high-bay luminaire, B) aluminum high-bay luminaire, C) aluminum lowbay luminaire with acrylic lens.
Light emitting diodes (LEDs)
Light emitting diodes (LEDs) are semiconductor materials that emit light when electricity
is passed through them. LEDs are used in thin-screen computer monitors, thin-screen
televisions, watches, exit signs, flashlights, traffic lights and many other applications.
Their appeal lies in their energy efficiency and longevity.
A principle challenge for white light LEDs is converting the colored light produced by an
LED into white light, which a combination of many colors of light. To do so, many LED
produce UV light to stimulate phosphors which emit red, green and blue light in the
proper proportion to make white light. Another approach is employed by organic LEDs,
which may someday be mass-produced using ink jet technology on a substrate.
The efficiency of white light LEDs is
approaching the efficiency of
fluorescent lights at about 25%.
Theoretically, LEDs could be 100%
efficient, which is equivalent to 683
lm/W. Current commercial and
household LEDs produce about 50100 lm/W. Lab prototypes can
produce up to 200 lm/W at 2,700 K.
The rated lifetime of LEDs is about
50,000-100,000 hours.
A principle advantage of LEDs is that
they produce uni-directional light.
Thus, light from LEDs can be aimed
directly at target without a reflector
and the associated losses. In
contrast, incandescent, fluorescent
and HID lamps produce light in all
directions and use reflectors to direct
LED lights in a Walmart in Suzhou,China
8
light onto a target.
The combination of high efficiency, long life and unidirectional light is often very
powerful. For example, many older traffic lights use 150-W incandescent light bulbs
that last about 1 year and are covered by red, yellow and green filters. Replacement
LED lights that directly generate red, yellow and green light consume about 15 W and
last about 5 years.
Comparative Characteristics
The efficiency of converting electricity to light can be measured as the ratio of light
output (lm) and electrical power (W). All common types of electric lights except
incandescent lights require a ballast to regulate the voltage to the lamp. Thus, the
lighting efficiency should include the electricity consumed by both the lamp and ballast.
The lighting output of most types of lights degrades over the lifetime of the light, thus
the mean lighting output should be used when calculating energy efficiency. The
approximate lighting efficiencies of common types of lighting systems (including
ballasts), and other characteristics are shown in the table below.
Light Type
Efficiency
CRI
Lifetime
Lumen
Restrike
(Lm/W)*
(hours)
Maint.
Time
Incandescent
18
99
750
Good
Instant
Compact fluorescent
70
60
10,000
OK
Immediate
T12 Fluorescent
58
60
20,000
Good
Immediate
T8 Fluorescent
100
75
20,000
Good
Immediate
Metal halide
70
65
20,000
Fair
30 min
High-pressure sodium
96
22
20,000
Good
30 min
LEDs
120
80
80,000
Good
Immediate
*Typical lm/W calculated using mean lighting output (lm) and energy use (W) including
ballast.
Performance Metrics
Typical performance and cost data for common lamps and ballasts are shown below.
Fluorescent and HID lamps are generally specified by a nominal power draw and
nominal light output. However, the power to a lamp is regulated by a ballast. Thus, the
actual power draw of the lamps plus the ballast, and light output of the lamps is
determined by the ballast.
9
Example
4-ft T8 fluorescent lamps have a nominal power draw of 32 W each and
nominal light output of 2,710 lm each. Using data from the tables shown
below, calculate the actual power draw and lighting output of two 32-W
lamps when powered by a single low-output electronic ballast, and when
powered by a high-output electronic ballast.
The power consumption of a single low-output electronic ballast is 51 W and
the power consumption of a single high-output electronic ballast is 77 W.
Thus,
Power input of 2 lamps and the ballast for low output ballast = 51 W
Power input of 2 lamps and the ballast for high output ballast = 77 W
The actual light output of a lamp is the product of the nominal rated light
output and the ballast factor associated with the ballast. Thus, the actual
light output of two 32-W lamps with nominal rated output of 2,710 lm each,
when powered by a low-output electronic ballast with ballast factor 0.75 is:
Light output (low output ballast) = 2 lamps x 2,710 lm/lamp x 0.75 = 4,065 lm
If the same lamps were powered by a high-output electronic ballast with
ballast factor 1.20 the actual light output would be:
Light output (high output ballast) = 2 lamps x 2,710 lm/lamp x 1.20 = 6,504
lm
Similarly, a metal halide lamp may be labeled with a nominal power draw of 400 W and
nominal light output of 23,500 lm. However, as shown in the tables below, the lamp
and the ballast together draws 460 W. HID ballasts generally have a ballast factor of 1.0.
Thus, the actual light output of HID lamp is equivalent to the nominal light output of the
lamps.
10
Fluorescent Lamps
Type
Nominal
Power
(W)
Rated
Life
(hr)
Mean
Output
(lm)
CRI
Cost
($)
34
40
20,000
20,000
2,280
2,910
62
73
1.40
4.00
32
32
32
20,000
24,000
20,000
2,710
2,710
2,625
78
75
78
1.90
2.60
11.00
60
95
110
12,000
12,000
12,000
5,060
6,960
7,740
62
60
60
3.90
6.00
13.00
59
59
86
15,000
15,000
18,000
5,310
5,150
7,200
75
75
75
7.80
24.10
17.70
4-ft T12
48-in T12 34-W
48-in T12 40-W
4-ft T8
48-in T8 32-W
48-in T8 32-W, long life, low merc
48-in T8 32-W, cover guard
8-ft T12
96-in T12 60-W
96-in T12 95-W
96-in T12 110-W
8-ft T8
96-in T8 59-W
96-in T8 59-W, cover guard
96-in T8 86-W
Fluorescent Ballasts
Type
4-ft T12
Fluor F34T12 Electromagnetic
4-ft T8
Fluor F32T8 Electronic (Low Output)
Fluor F32T8 Electronic (Normal Output)
Fluor F32T8 Electronic (High Output)
8-ft T12
Fluor F96T12 Electromagnetic
Fluor F96T12 Electromagnetic
Fluor F96T12 Electromagnetic
8-ft T8
Fluor F96T8 Electronic
Fluor F96T8 Electronic
Lamps
Lamp
Power
(W)
Ballast
Power
(W)
Ballast
Factor
2
34
68
.87
2
2
2
32
32
32
51
58
77
.75
.87
1.20
2
2
2
60
95
110
112
203
237
.88
.91
.95
2
2
59
86
110
160
.85
.88
Cost
($)
$36
$15
$36
$25
$29
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Metal Halide Lights
Lamps/fix
kW/fix
Lum/fix
Hours/lamp
Cost/lamp
Cost/fix*: Low Bay
Cost/fix*: High Bay
CRI
175 W
250 W
360 W
400 W
1,000 W
1
0.210
8,800
10,000
$27
$225
--65
1
0.295
13,500
10,000
$26
$215
--65
1
0.420
23,500
20,000
$50
$250
$110
65
1
0.460
23,500
20,000
$23
$250
$110
65
1
1.080
66,000
12,000
$74
$205
$235
65
High-Pressure Sodium Lights
Lamps/fix
kW/fix
Lum/fix
Hours/lamp
Cost/lamp
Cost/fix*
CRI
70 W
1
0.088
5,450
24,000
$27
$163
22
100 W
1
0.128
8,550
24,000
$23
$165
22
150 W
1
0.185
14,400
24,000
$21
$160
22
High-Bay Fluorescent Lights
T8
T8
T8
Lamps/fix
4
6
8
kW/fix
0.156
0.234
0.312
Lum/fix
13,680
20,520
27,360
Hours/lamp
24,000
24,000
24,000
Cost/lamp
$2.50
$2.50
$2.50
Cost/fix*
$120
$150
$200
Cost/occ sen
$70
$70
$70
CRI
85
85
85
* Fixture cost includes lamp, ballast and luminaire
250 W
1
0.300
27,000
24,000
$21
$196
22
400 W
1
0.465
45,000
24,000
$19
$216
22
1,000 W
1
1.110
126,000
24,000
$83
$360
22
T5
4
0.236
24,000
24,000
$15
$170
$70
85
T5
6
0.354
36,000
24,000
$15
$230
$70
85
T5
8
0.472
48,000
24,000
$15
$300
$70
85
12
High-Bay LED Lights
LED
4
Lamps/fix
0.080
kW/fix
8,000
Lum/fix **
100,000
Hours/lamp***
80
Cost/lamp
340
Cost/fix*
70
Cost/occ sen
80
CRI
* Fixture cost includes lamp, ballast and luminaire
Lighting Design
The Illuminating Engineering Society (IES) lumen method calculates the illuminance on a
workplane, Ew (fc), as:
Ew = Cu x F / Aw
where Cu is the coefficient of utilization, F is the total lumens produced by the lamps,
and Aw is the area of the work plane. Cu is a calculated from a manufacturer-supplied
table based on the type of luminaire, room geometries and surface reflectivities. Typical
Cus range from about 0.2 to 0.6 (Kreider and Rabl 1994) Heating and Cooling of
Buildings.
This equation can also be written as
Ew = Cu x (LPF x N) / Aw
Where LPF is the lumens per fixture and N is the number of fixtures. In fluorescent
lights, lumens per fixture LPF is the product of the number of lamps, NL, lumens per
lamp, LPL, and the ballast factor, BF.
LPF = NL x LPL x BF
To determine how many fixtures are needed simply solve this equation for N.
N = (Ew x Aw) / (Cu x LPF)
Values of the coefficient of utilization, CU, for typical 4-lamp fluorescent troffer fixtures,
400-W high-bay metal halide fixtures and 6-lamp high bay fluorescent fixtures are
shown in the tables below.
13
CU values for recessed 2’ x 4’ fixture with acrylic lens and 4 lamps
(www.columbialighting.com)
CU values for 8-ft 4-lamp or 4-ft 2-lamp fluorescent fixture (www.goodmart.com)
CU values for high-bay 400-W MH or HPS fixture (www.cooperlighting.com)
14
CU values for high-bay six-lamp ORION 416 HPM fluorescent fixture
(www.orionlighting.com)
In each table CU depends on the room cavity ratio, RCR, where
RCR = 5 x h x (w + l) / (w x l)
CU also depends on the reflectivity of the ceiling, rc, and the reflectivity of the walls, rw.
Most paint color chips report Light Reflecting Value (LRV), which is the reflectivity. Light
surfaces have a high reflectivity.
Source: http://www.squidoo.com/LRV
Electrical Lighting Design Example
Determine the number of 400-W metal halide fixtures and 230-W high-bay
fluorescent fixtures required to light a space with the following characteristics:
Ew = 40 fc
W = width = 50 ft
L = length = 100 ft
H = height = 25 ft
Rc = reflectivity of ceiling = 50%
Rw = reflectivity of walls = 50%
Solution:
15
RCR = 5 x h x (w + l) / (w x l) = 5 x 25 x (50 + 100) / (50 x 100) = 3.75 ~ 4.0
CU (400-W metal halide) = 0.57
CU (230-W high-bay fluorescent) = 0.69
LPF (400-W metal halide) = 23,500 lm
LPF (230-W high-bay fluor, w/ 3 2-lamp, 1.2 BF, 78-W ballasts at 8,000 hrs) = 3 x
6,840 lm = 20,520 lm
N = (Ew x Aw) / (Cu x LPF)
N (400-W metal halide) = (40 x [50 x 100]) / (.57 x 23,500) = 14.9 ~ 15 lights
N (230-W high-bay fluorescent) = (40 x [50 x 100]) / (.69 x 20,520) = 14.1 ~ 14 lights
Lamp Replacement Costs
Overtime, lamps fail and need to be replaced. Thus, economic analysis of lighting
upgrades should consider lamp replacement costs.
The number of lamps that must be replaced each year, Nr, can be calculated as:
Nr = Nt x AOH / LL
Where:
Nt = total number of lamps in operation
AOH = annual operating hours
LL = lamp lifetime
Lamp Replacement Cost Example
Consider lamp replacement savings from replacing 320 400-W MH fixtures with
320 6-lamp HBF fixtures if the lights operate 8,000 hours per year.
The number of lamp replacements would be about:
MH: (320 fix x 1 lamps/fix) x 8,000 hours/year / 20,000 hours = 128 lamps/year
T8: (320 fix x 6 lamps/fix) x 8,000 hours/year / 30,000 hours = 512 lamps/year
The cost of a 400-W MH lamp is about $23, and T8 lamps cost about $3 each. The
hourly wage for a skilled-trade electrician, including all benefits, is about $65 per
hour. Assuming it would take one worker about 30 minutes to replace either a
single MH lamp or 6 T8 lamps, the annual maintenance costs are about:
MH: 128 lamps/year x ($23 /lamp + (30/60 hours/lamp x $65 /hour)) = $7,104
/year
16
T8: 512 lamps/year x ($3 /lamp + (30/60 hours / 6 lamps x $65 /hour)) = $4,309
/year
Thus, the annual maintenance savings would be about:
$7,104 /year - $4,309 /year = $2,795 /year
Economics of Lighting Upgrades
The methods described above can be used to determine the economics of lighting
upgrades. The method typically involves the following steps.






Calculate how many of the proposed lights are needed to deliver the required
number of footcandles in the space.
Calculate the annual energy cost savings of replacing the current lights with the
proposed lights.
Calculate the annual relamping cost savings, including both labor and material
costs.
Calculate total annual cost savings including both annual energy and annual
relamping savings.
Calculate the one-time implementation cost of replacing the current lights with
the proposed lights.
Calculate the simple payback of the investment.
The performance and coefficient of utilization data from the preceding sections can be
used in these calculations.
Lighting Upgrade Economics Example
A facility has 25 fixtures with 400-W high pressure sodium (HPS) lamps. A lighting
upgrade to 6-lamp T8 high-bay fluorescent (HBF) fixtures is proposed. The lights
operate 6,000 hours per year and the average cost of electricity is $0.10 /kWh. The
hourly wage for an electrician is $50 per hour. It takes an electrician 15 minutes to
replace either a single HPS lamp or 6 T8 lamps. It takes an electrician 30 minutes to
replace a HPS fixture with a new HBF fixture.
Determine annual cost savings including energy and lamp replacement costs, the
implementation cost, and simple payback of the project. The space has the following
characteristics:
Ew, required = 50 fc
W = width = 150 ft
L = length = 100 ft
H = height = 25 ft
17
Rc = reflectivity of ceiling = 70%
Rw = reflectivity of walls = 70%
Solution:
The number of HBF fixtures required would be:
RCR = 5 x h x (w + l) / (w x l) = 5 x 25 x (150 + 100) / (150 x 100) = 2.0
CU (HBF) = 0.93
LPF (HBF) = 20,520 lm
N (HBF) = (Ew x Aw) / (Cu x LPF)
N (HBF) = (50 x [150 x 100]) / (.93 x 20,520) = 34 fixtures
The energy cost savings would be:
Esav = [(25 fix x .465 kW/fix) – (34 fix x .234 kW/fix)] x 6,000 hr/yr
Esav = 22,014 kWh/yr
ECsav = 22,014 kWh/yr x $0.10 /kWh = $2,201 /yr
The number of annual lamp replacements would be:
HPS: (25 fix x 1 lamps/fix) x 6,000 hours/year / 24,000 hours = 6 lamps/year
HBF: (34 fix x 6 lamps/fix) x 6,000 hours/year / 24,000 hours = 51 lamps/year
The annual lamp replacement costs would be:
HPS: 6 lamps/year x ($19 /lamp + (.25 hr/lamp x $50 /hr)) = $189 /yr
HBF: 51 lamps/year x ($2.5 /lamp + (.25 hr/ 6 lamps x $50 /hr)) = $234 /yr
The annual lamp replacement savings would be:
$189 /year - $234 /year = -$45 /year
The total annual savings would be:
$2,201 /year - $45 /year = $2,157 /year
The implementation cost and simple payback would be:
IC = 34 fix x [$200 /fix + (.50 hr/fix x $50 /hr)] = $7,650
SP = $7,650 / $2,157 /yr x 12 mo/yr = 43 months
18
Natural Lighting Design
Natural lighting uses light through skylights in the roof of a building or windows in the
walls of a building.
Illuminance from Skylights
The Illuminating Engineering Society (IES) lumen method to calculate the illuminance on
a work plane, Ew (fc), from the illuminance on a horizontal skylight Esl (fc) is:
Ew = Esl x Cu x transmissivity of the skylight x transmissivity of the well x Asl / Aw
Where Cu is the coefficient of utilization, Asl is the area of the skylight and Aw is the
area of the work plane.
Cu is a function of ceiling reflectivity, pc , wall reflectivity, pw, and the room cavity ratio,
RCR. Values of Cu for skylights are tabulated in Table 13.5 of Kreider and Rabl, 1994,
Heating and Cooling of Buildings. An adequate approximation is given by:
Cu = 1.016898 + 0.074074 pc + -0.14778 RCR + 0.111111 pw + 0.037037 pc2 + 0.008133
RCR2 + 0.125 pw2
The room cavity ratio, RCR, is:
RCR = 5 x h x (w + l) / (w x l)
where h is the height of the skylight over the work plane, w is the width of the room and
l is the length of the room.
Design values of the illuminance on a skylight, Esl, can be found in Figures 13.4 – 13.6 of
Kreider and Rabl, 1994, Heating and Cooling of Buildings. Alternately, Esl can be
calculated from the total radiation on a horizontal surface Ih (Btu/hr-ft2) by assuming
that the illuminance of sunlight is 110 lm/W.
Esl (fc) = Ih Btu/hr-ft2 / 3.413 Btu/W-hr x 110 lm/W x 1 fc/(lm/ft2)
According to a local roofing company in 2002, the material and installation for a 4 ft by 4
ft skylight with a 10-foot shaft would cost about $2,000.
Illuminance from Skylights Example
A 50 ft by 50 ft room with a 25 foot ceiling has 50 ft2 of skylights. The total
solar radiation on the skylights is 300 Btu/hr-ft2. Calculate the illuminance
on the floor. The reflectivity of the walls is 0.70 and the reflectivity of the
ceiling is 0.70. The average transmissivity of each skylight is 0.80 and the
average transmissivity of each skylight well is 0.90.
19
Assuming that the illuminance of sunlight is 110 lm/W, the illuminance on a
skylight, Esl, is:
Esl = Ih Btu/hr-ft2 / 3.413 Btu/W-hr x 110 lm/W x 1 fc/(lm/ft2) = 9,669 fc
The room cavity ratio, RCR, is:
RCR = 5 x h x (w + l) / (w x l) = 5
The coefficient of utilization, Cu, is:
Cu = 1.016898 + 0.074074 pc + -0.14778 rcr + 0.111111 pw + 0.037037 pc2 +
0.008133 rcr2 + 0.125 pw2 = 0.690
The illuminance on a work plane, Ew (fc), is:
Ew = Esl x Cu x transmissivity of skylight x transmissivity of well x Asl / Aw =
96 fc
Illuminance from Vertical Windows
The IES recommends an illuminance of about 20 fcs for warehouse spaces and 50 fc for
precision work. The general equation to calculate the illuminance on a work plane, Ew
(fc), from the illuminance on a vertical window Ev (fc) is:
Ew = Ev x Cu x transmissivity of the window
Where Cu is the coefficient of utilization. Cu is a function of the window length and
height, room depth and the distance between the window and the work plane
(expressed as a fraction of the room depth). Values of Cu for windows are tabulated in
Table 13.8 or Kreider and Rabl, 1994, Heating and Cooling of Buildings.
Design value of the illuminance on a vertical window, Ev, can be found in Figures 13.4 –
13.6 of Kreider and Rabl, 1994, Heating and Cooling of Buildings. Alternately, Ev can be
calculated from the total radiation on a vertical surface Iv (Btu/hr-ft2) by assuming that
the illuminance of sunlight is 110 lm/W.
Ev (fc) = Iv Btu/hr-ft2 / 3.413 Btu/W-hr x 110 lm/W x 1 fc/(lm/ft2)
If the window is shaded from direct solar radiation, then the Iv should be the diffuse
component of solar radiation.
20
LightSim Daylighting Analysis Software
LightSim daylighting analysis software simulates hour-by-hour illuminance on a work
plane using TMY2 meteorological data. It is specifically designed to assess the feasibility
of daylighting in buildings. LightSim can quickly determine the fraction of time that
various daylighting designs can meet or exceed a target illumination on a work plane.
LightSim is available at no cost from the University of Dayton IAC.
Photo Controls
Photo controls turn lights on and off depending on lighting levels or occupancy. In
indoor lighting applications, photo controls are most often used with fluorescent or
incandescent lights since these lights turn on and off quickly. Photo controls are seldom
used with HID lighting in indoor applications, because of the 15-minute restrike time
required for HID lighting to regain full output.
Photo Sensors
Photo sensors measure light levels and control lights based on the difference between
the measured light level and a set point.
In outdoor applications, photo sensors turn lights off during the day and on during night,
with an average on-time of 12 hours per day. Most outdoor HID lights come with a ½inch knockout or an 11/16-inch hole for easy screw-in mounting. Most photo sensors
have built-in delays to prevent false cycling from headlights, etc. Photo sensors
typically cost less than $15 each and can be installed in less than ½ hour. Thus, it is
virtually always cost-effective to install photo sensors on outdoor lights to prevent lights
from running during daylight hours. In indoor applications, photo sensors turn off
unnecessary lights in day lit spaces.
Occupancy Sensors
Occupancy sensors turn lights on when a space is occupied and turn lights off about 4
minutes after the space is unoccupied. Most occupancy sensors use infrared sensors to
detect body heat in motion.
In commercial buildings, occupancy sensors are especially effective in lightly used areas,
such as lavatories or conference rooms, or in rooms where lights may be left on
inadvertently. In manufacturing facilities, occupancy sensors are especially effective in
ware house areas with limited traffic between rows of stacks. Residential occupancy
sensors cost about $15 each and commercial/industrial quality occupancy sensors cost
between $80 and $200 each.
Ballast and Lamp Disposal
Ballasts manufactured before 1979 contained wet-capacitors with the hazardous waste
PCB. After 1979, ballasts used dry capacitors and contain no appreciable hazardous
21
wastes. Because very few pre-1979 ballasts remain, most states allow post-1979
ballasts to be disposed of in normal waste streams.
Fluorescent and HID lamps contain small amounts of mercury in the phosphor powder.
Mercury is a potent neurotoxin and is harmful to both animals and humans. When
unbroken lamps are disposed of in landfills, virtually no mercury leaches into the
environment. However, if lamps are incinerated, the mercury is transported through
the atmosphere to water, animals and humans. Spent lamps can also be recycled;
however, some studies indicate that more mercury is released into the environment
during recycling than by placing the lamps in landfills.
Currently, lamp disposal is regulated on a state-by-state basis, or indirectly by the 1990
RCRA, which recognizes mercury as a hazardous waste. In many states, all traditional
spent lamps from businesses are considered hazardous waste irrespective of the
number of lamps being disposed. In this case, spent lamps should be sent to a
registered recycler or hazardous waste contractor. Under RCRA, small quantity
generators that dispose less than 350 4-foot lamps per month can legally dispose of
spent lamps into the municipal solid waste stream. In any case, if the municipal waste is
incinerated, it is recommended that the lamps be sent to an EPA-registered recycler or
hazardous waste disposal company. Be sure to research the credibility of the recycler or
waste management company. If the waste is not disposed of properly, the original
generator may be legally liable. Recyclers and hazardous waste handlers typically
charge about 40 cents per lamp for disposal or recycling.
For new lamp purchases, specify low-mercury lamps, which are commonly marked with
green end-caps. Low-mercury lamps have about 5 milligrams of mercury compared to
about 48 milligrams for 1985 vintage lamps. The additional cost for low-mercury lamps
is usually negligible, and in most states, spent low-mercury lamps can be deposited
directly in landfills instead of being sent to a lamp recycler. This saves disposal costs and
reduces potential environmental legal liability issues.
Compact fluorescent lamps contain about 4 mg of mercury. However, the 75%
reduction in energy use compared to incandescent lamps displaces mercury emissions
from coal fired power plants. The U.S. EPA estimates that the use of CFLs in place of
incandescent lamps results in over three times less mercury emissions.
22
Source: U.S. E.P.A., Information on CFLs and Mercury, 10/2010
Heating and Cooling Interactions
Reducing the lighting energy added to a conditioned space decreases the space cooling
load and increases the space heating load. From simple energy balances, the air
conditioning electricity savings can be estimated as:
[(Plights,pre - Plights,post) x hours/year ] / cooling
The additional heating energy can be estimated as:
[(Plights,pre - Plights,post) x hours/year] / heating
Where Plights is the power draw of the lights and  is the efficiency of the space
conditioning equipment.
Heating and Cooling Energy Example
If the lighting load were decreased from 50 kW to 40 kW, for 2,500 hours
per year during the cooling season, and the average efficiency (coefficient
of performance) of an air conditioner is 3.0, calculate the air conditioning
savings:
The air conditioning savings would be:
[(50 kW - 40 kW) x 2,500 hr/yr ] / 3.0 = 8,333 kWh/yr
23
If the lighting load were decreased by the same amount for 2,500 hours
during the heating season, and the average efficiency of a furnace was
75%, calculate the additional heating energy needed.
The additional heating energy would be about:
[(50 kW - 40 kW) x 2,500 hr/yr ] / 0.80 x 3,413 Btu/kWh = 107 x 106 Btu/yr
Note that when the heating and cooling periods are about the same length, as in this
example, the increased air conditioning and decreased heating costs may be nearly
equal. For this reason, they are sometimes ignored. In buildings with complex HVAC
systems, heating and cooling interaction effects can be more accurately modeled by
building energy simulation software.
Internal Heat Gain from People
Typical sensible, latent and total heat rates given off by people are shown in the table
below (ASHRAE Fundamentals, 2005). The sensible heat gain results from radiation and
convection from the human body to the air. The latent heat gain is the energy required
to condense the water vapor given off by human respiration and perspiration. The
latent heat gain is the product of the mass of water vapor from humans and the
enthalpy of evaporation for water vapor at atmospheric pressure.



 Btu 
Q latent  mw hfg  mw  1,076 

 lbw 
Average Person
At rest
Light work
Heavy work
Qtotal
350 [Btu/hr]
100 W
640 [Btu/hr]
185 W
1600 [Btu/hr]
Qsensible
210 [Btu/hr]
60 W
315 [Btu/hr]
90 W
565 [Btu/hr]
Qlatent
140 [Btu/hr]
40 W
325 [Btu/hr]
95 W
1035 [Btu/hr]
470 W
170 W
300 W
Internal Heat Gain from Electrical Equipment
All electricity consumed in a building is eventually converted into sensible heat. Thus,
the heat gain from electricity is equivalent to the electricity use inside a building.
The average American house in uses about 11,000 kWh/yr. To gain intuition about how
much heat this is, assume a house uses 8,760 kWh/year. If so, the average rate of heat
gain is about:
24
 kWh 
1
8760 


 yr  8760
 yr 
 h   1 kW
 
Only the electricity consumed indoors becomes heat gain to the space. If 25% of this
electricity was used for outdoor lighting or consumed by the outdoor air conditioner
compressor and condenser fan , the average internal heat gain from electricity use
would be:

 Btu 
 Btu 
Q elec  1 kW  75%  3,413 
 2,560 


 kWh 
 hr 
Alternately, the following table shows average operating characteristics of residential
electric appliances.
25
Equipment
Kitchen
Coffee Maker
Dishwasher
Microwave Oven
Toaster Oven
Refrigerator-Freezer*
Lighting
18-W Compact Fluorescent
60-W Incandescent Lamp
100-W Incandescent Lamp
Torchiere Lamp-Halogen
Bedroom and Bathroom
Hair Dryer
Waterbed Heater
Laundry Room
Clothes Dryer*
Clothes Washer*
Home Electronics
Desktop PCs
Notebook PCs
Desktop Computer Monitors
Stereo Systems
Televisions
Analog, <40"
Analog, >40"
Digital, ED/HD TV, <40"
Digital, ED/HD TV, >40"
Set-top Boxes
DVD/VCR
Video Game Systems
Heating and Cooling
Dehumidifier
Furnace Fan
Ceiling Fan (only fan motor)
Space Heater
Water Heating
Water Heater-Family of 4
Water Heater-Family of 2
Portable Spa
Miscellaneous
Rechargeable Power Tool
Vacuum
Pool Pump
Well Pump
Lawn Sprinkler
Aquarium Equipment
* - Estimated Value from available data
Power Draw (W)
Active
1,000
1,200
1,500
1,051
100
Idle
Operating Time (hours/year)
Off
70
Active
0
3
38
365
70
37
6,600
18
60
100
300
1,189
672
672
1,460
710
350
50
3,051
2,800
300
359
392
75
25
42
33
97
86
156
150
234
20
17
36
600
295
35
1,320
4,500
4,500
4,350
13
542
1,000
725
11
24
4
2
1
30
2
2
1
3
4
0
13
36
20
3
1
2,990
2,368
1,865
1,510
1,860
1,095
1,825
1,095
1,825
6,450
170
405
1
1,620
1,350
2,310
584
275
64
32
25
4
Idle
229
Off
8,493
8,690
330
935
875
1,810
5,440
5,457
6,020
5,440
6,900
0
5,150
560
2,310
3,430
7,795
8,735
73
37
792
115
0
6,534
Residential electric equipment energy use.
Source: DOE, Building Energy Data Book, March 2011
In commercial buildings, lighting energy density is typically about 1.5 W/ft2 and the plug
load density for computers, copiers, etc. is about 0.5 W/ft2. All of this becomes heat gain
into the space.
26
Reducing Energy Use and Cooling Loads with Energy Efficient
Appliances and Equipment
Energy Star is a standard created by the United States
Environmental Protection Agency to identify energy efficient
lighting, equipment and even buildings. Energy Star certified
products typically use 30% or more less energy than
conventional products. The table below shows the increased
energy efficiency of Energy Star rated products compared to
conventional products.
Equipment
Cloth washer (full size)
Dish washers
Refrigerators
Water coolers
Microwaves
Toasters
Coffee maker
Audio Video Equipments
Battery chargers
Desktop computers
Displays and monitors
Laptops
Television
Set top box
Ventilation Fans
Ceiling Fans
Light Bulbs
Decorative lights and light strings
Roof top air conditioning
Air conditioning units (Central)
Air conditioning units (room)
Boilers
Furnaces (gas and oil)
% more energy
efficient over
conventional
products
30%
10%
20%
45%
20%
15%
30%
60%
35%
33%
20%
33%
40%
40%
60%
50%
65%
70%
12%
14%
10%
6%
15%
Energy Star Equipment efficiency gain compared to typical product.
27
Example
Consider a house that uses the following electric equipment: cloth washer, dish
washer, refrigerator-freezer, desktop PC, desktop monitor, television, microwave
oven, toaster oven and coffee maker.
a) Using data from the “Residential electric equipment energy use” table, calculate
the total annual energy use of the equipment (kWh/yr).
To demonstrate how to calculate annual energy use, consider the case of “Desktop
PC”. The annual consumption is calculated as:
The annual energy use for all equipment is the sum of the annual consumption of all
the individual equipment.
b) Using data from the “Energy Star Equipment efficiency gain compared to typical
products” table, calculate the total annual energy use of Energy Star equipment
(kWh/yr).
The annual energy use for Energy Star equipment is:
28
Energy Star House
Power Draw (W)
Equipments
Clothes Washer
Dishwasher
Refrigerator-Freezer
Desktop PC
Desktop Computer Monitor
Television
Microwave Oven
Toaster Oven
Coffee Maker
% more energy efficienct
30%
10%
20%
33%
20%
40%
20%
15%
30%
Active
210.0
1,080.0
80.0
50.3
33.6
58.3
1,200.0
893.4
700.0
Idle
Annual Usage (hours/year)
Off
Active
2.7
0.8
1.3
0.8
2.4
2.4
49.0
0.3
392
365
6,600
2,990
1,865
1,860
70
37
38
Idle
Off
330
875
5,440
6,020
6,900
8,690
229
8,493
Total energy use of Energy Star house (kWh/yr) =
Annual
Consumption
(kWh/year)
82.3
394.2
528.0
158.4
68.2
125.0
104.9
32.6
40.2
1,533.8
c) Calculate the overall percent energy use reduction of the energy star equipment
compared to typical equipment.
Input
Energy use
Typical House
Energy Star House
Calculation
% energy use reduction = (Typ. - ES)/Typ.
1,972.5
1,533.8
22%
Lighting References
American Council for an Energy-Efficient Economy, 2000, “Guide to Energy-Efficient
Commercial Equipment”, Washington, D.C.
Energy Information Administration, 1996, “Residential Lighting Use and Potential
Savings”
DOE/EIA-0555(96)/2, U.S. Department of Energy, Washington, DC,
http://www.eia.doe.gov/emeu/lighting/.
Energy Information Administration, 2002, “U.S. Lighting Market Characterization,
Volume 1: National Lighting Inventory and Energy Consumption Estimate”, U.S.
Department of Energy, Washington, D.C.
Granger, 2001, “Grainger Industrial Supply Catalog 2000-2001”, No. 391.
Heschong Mahone Group, 1999, “Daylighting in Schools” and “Skylighting and Retail
Sales”, Pacific Gas and Electric, http://www.h-mg.com/Daylighting/daylighting_and_productivity.htm
Kreider, J.F. and Rabl, A., “Heating and Cooling of Buildings”, 1994, McGraw-Hill Inc.
McDonough, 2008, http://www.mcdonough.com/miller.html.
29
Orion, Plymouth WI, www.orionlighting.com
Romm and Browning, 1999, “Greening the Building and the Bottom Line”, Global Energy
Conference, Vancouver, May.
Suozzo, M., Benya, J., Hydeman, M., Dupont, P., Nadel, S. and Elliot, N., “Guide to
Energy Efficient Commercial Equipment”, 2000, American Council for an Energy Efficient
Economy.
Technology Review, 2003, “LED vs. the Lightbulb”, May, pgs. 30-36.
University of Dayton Industrial Assessment Center, 2008, Dayton, OH
30