Supplementary Material for Chapter 24
A Triple-Bottom-Line Analysis of Energy
Efficient Lighting
This chapter is published as:
Lindstrom, TD, Middlecamp CH. 2016. A Triple-Bottom-Line Analysis of Energy
Efficient Lighting. In: Byrne L (ed) Learner-Centered Teaching Activities for
Environmental and Sustainability Studies. Springer, New York. DOI 10.1007/9783-319-28543-6_24
Timothy Lindstrom and Catherine Middlecamp
Nelson Institute for Environmental Studies
University of Wisconsin-Madison, Madison, WI USA
[email protected]
[email protected]
This file contains the following supplementary material:
 A: Student Worksheet
… beginning on p. 1
 B: Instructor’s Guide
… beginning on p. 12
 C: Introduction to Power and Energy
… beginning on p. 28
 D: Introductory Practice Problems
… beginning on p. 32
page 0
Supplementary Material A: Student Worksheet
UNION SOUTH MARQUEE: Evaluating the Switch1
Asking Questions
Energy efficient lighting is becoming the new norm in residences, businesses, and college
campuses across the United States. The University of Wisconsin-Madison is no exception. In
the past decade, roughly $10 million has been invested toward upgrading the lighting
infrastructure in campus buildings. In regards to sustainability, is the investment worth it?
This activity will seek to answer that question by analyzing a potential campus lighting project
from the perspective of the Triple Bottom Line.
Union South is an important social hub on the UWMadison campus. Like any student union, it offers a
variety of services for the campus community to take
advantage of. Among them is a sizeable screening room
known as the Marquee. The Marquee is located on the
second floor of Union South and seats 330 people. The
room features a stage and screen, making it a popular
venue for meetings, lectures, special events, and films.2
The lighting in the Marquee includes light bulbs of
different shapes, sizes and wattage. Among them are 11
stage lights in the ceiling in front of the wide screen (see
photograph). These lights are 18 feet above the floor,
which poses a safety hazard to custodial staff each time
they have to climb up and replace them. One solution is
to replace the current halogen lamps with long-lasting
but more expensive light emitting diode (LED) lamps.
Photo by Tim Lindstrom
Your task is to evaluate the sustainability of this potential
lighting upgrade and then make a recommendation. These questions will guide you:
 Will this project be worth it from an economic perspective?
 Will it be beneficial to the environment?
 Does it positively impact the community?
This framework for evaluating sustainability is known as the Triple Bottom Line, and can be
applied to individual decisions as well as the choices made by much larger entities, like a
university.
1
This activity was designed by Tim Lindstrom (graduate student, Nelson Institute) and Dr. Cathy Middlecamp
(Nelson Institute, University of Wisconsin-Madison). Technical information about the lighting at Union South was
provided by Roxanne Hammer, Supervisor, Wisconsin Union Facilities Management.
2
The Marquee at Union South: http://www.union.wisc.edu/marquee.htm
page 1
Preparing to Investigate
LEDs boast the longest lifespan of any light bulb. As a result, this switch would reduce the
frequency with which the bulbs need to be replaced, keeping the custodial staff out of harm’s
way. LEDs also operate at a lower wattage, thereby reducing the electricity costs for UWMadison as well as the demands on Madison Gas & Electric, the local power plant.
Currently, LEDs also boast the biggest hit to your wallet. The bulbs cost more in the short run,
but over time would Union South recoup its investment through lower electricity bills? In
addition, reduced energy demands mean reduced emissions of carbon dioxide and other
pollutants.
GE 75-watt halogen lamp
Philips 13-watt LED lamp
Photos by Tim Lindstrom
You have three tasks relating to these stage lights:
(1) Calculate the payback period for the lighting switch.
(2) Calculate the change in CO2 emissions as a result of using more efficient lighting.
(3) Reflect on the societal impact – not just of this relatively small decision by Union South,
but the impact to society of using more efficient lighting in general.
As you complete these three tasks, be conscious of how they apply to the Triple Bottom Line,
which states that an action or process is sustainable if it yields positive returns to the economy,
the environment, and the community.
The Triple Bottom Line
Graphic by Tim Lindstrom
page 2
Pre-activity Survey
Name ______________________
Date _________________
Photo by Tim Lindstrom
1. How familiar are you with the environmental issues that connect to light bulbs?
A.
B.
C.
D.
Environmental issues? Hasn’t really crossed my mind.
I’ve heard that there are environmental issues but cannot name any.
I could name at least one of the environmental issues.
I understand the issues well enough to have my own opinions about them.
In the space below, fill in blank according to your response:
A or B – Take a guess at a possible issue:
C – List one or more environmental issues.
D – Provide at least one of your opinions.
page 3
Pre-activity Survey
Name ______________________
Date _________________
2. Is it a smart move to buy LEDs to replace incandescent and fluorescent bulbs?
A.
B.
C.
D.
E.
NO. You lose money.
NO. The money can be better used elsewhere.
YES. You save money.
YES. You lose money but it's good for the environment.
YES. I've got another reason.
In the space below, explain your reasoning:
page 4
Gathering Evidence – Economic Health
Calculating the Payback Period
Why are we doing this?


to apply the Triple Bottom Line to lighting decisions on campus
to recognize scenarios where more efficient lighting may be worth the expense
Let’s shed some light on the economics of this decision. Table 1 provides data for the halogen
lamp formerly used at the Marquee and the new LED lamp.
Halogen
Cost
(per bulb)
$8.37
Lifetime
(hours)
3,000
LED
$46.85
45,000
Light source
Watts
75
13
Daily use
(hours)
Labor cost to install
(per bulb)
6, 10, or 14
$25
Table 1 – Comparison of a halogen and an LED bulb
We provide 3 possible daily use values: low (6 h/day), average (10 h/day), and high (14 h/day).
Your group will be assigned one of these values. You will compare your results later on to better
understand how the daily use of the lights at the Marquee affects the payback period.
Follow the steps below to calculate the payback period for the Marquee lighting switch. For each
step, enter your results in the blanks next to the corresponding number on the Data Sheet.
1. Form a team of 3. Enter your assigned value for the daily lighting use of the Marquee on
your Data Sheet.
2. Calculate the cost to purchase and install the 11 stage lights:
a. If the lights are halogens.
b. If the lights are LEDs.
3. Find the difference between 2(a) and 2(b). This is the initial extra cost of switching to
LEDs. The payback period will be the amount of time it takes to recoup this investment.
4. Calculate the monthly energy requirements in kW-h of using each type of light. For our
purposes, one month will be 30 days.
5. Convert your answers from Step 4 into monthly energy costs for each type of light. Use a
value of $0.11/kW-h for your conversions.
6. Calculate how many days it will take for both the halogen and LED bulbs to burn out and
need to be replaced. Convert days to months and round to the nearest month.
7. You now have all the data you need to calculate the payback period. It is up to your
group to figure out how to do this. Your payback period should be given in months.
If you run into trouble, ask your instructor.
page 5
Gathering Evidence – Economic Health
Calculating the Payback Period
DATA SHEET
1. Hours of daily lighting use at the Marquee: ____________________
2. Cost to purchase and install the 11 lights.
a. halogen bulbs:
b. LEDs:
3. Initial cost of switching to LEDs:
4. Monthly energy requirements.
a. halogen bulbs:
b. LEDs:
5. Monthly energy costs.
a. halogen bulbs:
b. LEDs:
page 6
Gathering Evidence – Economic Health
Calculating the Payback Period
DATA SHEET
6. Number of months to replace bulbs:
a. halogen bulbs:
b. LEDs:
7. Calculating the payback period:
Final value for payback period: ______________________________
page 7
Analyzing and Interpreting Evidence – Economic Health
Calculating the Payback Period
1. Confer with teams who used a different value for the daily use of the LED stage lights
at the Marquee. Does the daily usage have a significant effect on the payback period?
______ yes
_____no
Provide values to justify your answer.
2. Using your value for daily usage, Union South would be expected to replace the LED
stage lights in approximately ____________ (give month) of the year ________.
Show calculation:
3. Union South would have to replace a halogen bulb _____ times before an LED would be
expected to burn out.
Show calculation:
4. The total amount of savings Union South will enjoy using the eleven LED stage lights
before they burn out is expected to be ___________________.
Show calculation:
5. Is switching to LED lights at the Marquee an economically sustainable decision?
______ yes
_____no
Explain your answer.
page 8
Gathering Evidence – Environmental Health
Accounting for CO2 Emissions
Now let’s calculate the CO2 emissions at the local power plant as a result of using the lights.
Using your energy calculations from Part 1, determine the monthly CO2 emissions from using
the halogen and LED lights.
Note: Union South is powered by Madison Gas & Electric, which in turn is part of a larger
energy grid in the Midwest. In 2015, this grid emitted 1.61 pounds of CO2 per kW-h.3 Use this
value to determine the CO2 emissions.
1. Monthly CO2 emissions:
Halogen bulbs
Answer: ________ pounds of CO2 per month per 11 halogen bulbs.
Show calculation:
LED bulbs
Answer: _________ pounds of CO2 per month per 11 LED bulbs.
Show calculation:
3
Value obtained from the U.S. EPA: http://www.epa.gov/egrid.
page 9
Analyzing and Interpreting Evidence – Environmental Health
Accounting for CO2 Emissions
1. For the daily use value assigned to your team, determine the CO2 emissions avoided per
year by swapping the halogen bulbs for LEDs.
2. Calculate the total CO2 emissions (in pounds) that Union South will save over one full
lifetime of the LED bulbs.
3. Do you think that switching to LED lights at the Union South Marquee is an
environmentally sustainable decision? Explain your answer.
page 10
Reflecting on the Investigation
Connecting the Triple Bottom Line
1. We have yet to address the third component of the Triple Bottom Line: the community.
From a local standpoint, switching the Marquee lights to LEDs is a safety precaution for
the custodial staff. Explain how this can be considered a positive societal impact.
2. Thinking more about the big picture, how does switching to more efficient lighting
impact communities and societal health?
3. Drawing on the information from this activity, analyze the Marquee lighting switch in
terms of its sustainability. Outline your points below, connecting them to the elements of
the Triple Bottom Line. Finally, make a recommendation – should Union South move
forward with this lighting switch?
page 11
Supplementary Material B: Instructor’s Guide
UNION SOUTH MARQUEE: Evaluating the Switch4
INSTRUCTOR VERSION
GENERAL NOTES FOR INSTRUCTORS
In this version for instructors, the answers are in bold highlight. Parts of the activity for which
further explanation is provided are identified with a highlighted superscript1 that references an
endnote.
Student preparation and background:1
Prior to the activity, students need to have been introduced to the concepts of power and energy
and the time-dependent relationship between the two. Students also need to be able to convert
from watt-hours to kilowatt-hours and vice versa. The document Introduction to power and
energy (ESM-C), provides a short discussion on the two physical principles and their connection
to lighting. This document may be assigned to students prior to the lighting activity.
Students also should know some information about incandescent, CFL, and LED light bulbs.
The document Introductory Practice Problems (ESM-D), introduces students to basic features
of light bulbs and includes some practice calculations. Additional helpful online sources are
listed below.
 Energy.gov video – Energy 101: Lighting Choices
(http://energy.gov/eere/videos/energy-101-lighting-choices)
 energyNOW! video – Energy 101: Light Bulbs
(https://www.youtube.com/watch?v=Pk60-D61h34)
 Energy Star: two webpages on CFL and LED basics (Energy Star 2014; Energy Star
2014).
 Department of Energy: two webpages that provide lighting basics and a comparison
across energy efficient and incandescent bulbs (DOE 2013; DOE 2014).
 EPA: a webpage on environmental considerations for CFLs (EPA 2014).
 Lawrence Berkeley National Laboratory: a webpage that provides energy-related
resources for instructors and students (LBNL 2014).
Finally, students should be familiar with the triple bottom line.2 Instructors may introduce this
concept in lecture or assign a reading beforehand. The University of Wisconsin Sustainable
Management Program has a helpful webpage introducing the Triple Bottom Line (Board of
Regents 2014). Additional TBL references: Gibson 2006; Slaper and Hall 2011; Opp and
Saunders 2013.
4
This activity was designed by Tim Lindstrom (graduate student, Nelson Institute) and Dr. Cathy Middlecamp
(Nelson Institute, University of Wisconsin-Madison). Technical information about the lighting at Union South was
provided by Roxanne Hammer, Supervisor, Wisconsin Union Facilities Management.
page 12
A note about the highlighting:
The economic and environmental assessments in this activity depend upon an estimate of the
number of hours the lights are on each day. Rather than pick one value, the activity suggests
three scenarios that represent low, average, and high rates of use (for information about
implementation, refer to Part 3-ii under the Activities section of the book chapter). The
instructor version provides answers for all three scenarios, represented by different colors:
 Answers specific to 6 hrs/day (gray).
 Answers specific to 10 hrs/day (green).
 Answers specific to 14 hrs/day (turquoise).
 All other answers are highlighted in yellow.
A note about the pre-activity survey questions:
The original implementation of this activity begins with a survey administered using clickers.
Students also fill out and turn in the paper copy of the survey. If electronic polling devices are
not available, instructors may poll the students by a show of hands, present the survey questions
in an open discussion format, or forego the survey questions altogether. Further information
about the introduction to this activity can be found in Part 2 in the Activities section of the book
chapter.
ACTIVITIES
1. Introduction and Warm-up (10-15 min)
i.
A discussion helps prepare students for this activity. A list of prompts is provided in
ESM-B. Instructors may address these prompts in an all-class discussion or allow
students to respond in small groups first.
ii.
ESM-A includes two pre-activity survey questions (pp. 3-4) that may be used in
tandem or in place of the questions from the student worksheet.
iii.
Transition into the activity by explaining to students that they will be analyzing the
project from three different perspectives that follow the triple bottom line. This is a
good opportunity to reiterate what the triple bottom line is and how it is applied to
decision-making.
The following sections closely follow ESM-A. All page references refer to this file.
2. Economic Analysis (15-20 min)
This analysis examines the tradeoffs between short-term and long-term costs of efficient
lighting (p. 5). Students should discover that the initial investment in more efficient lighting
soon pays for itself and can lead to significant savings over the lifetime of the bulbs.
i.
Divide the class into groups of two or three. Each student should have a printed copy
of the handout (ESM-A), and each group should have a calculating device.
ii.
Using the data in Table 1 (p. 5), each group will perform a series of calculations,
eventually arriving at a simple payback period for the lighting upgrade. Estimates are
given for three lengths of time that the lights are on each day: 6, 10, or 14 hours.
Instructors should assign one of the three values to each group. Groups will compare
their results later in the activity.
page 13
iii.
iv.
v.
vi.
The handout walks students step-by-step through an initial set of calculations (p. 5).
These calculations are not the payback period; rather, they are the elements needed
to then calculate the payback period. Details of the specific calculations are provided
in ESM-B (p. 16).
Students are challenged to calculate the payback period of the lighting project using
the lighting data and the results of their initial calculations. Instructors are
encouraged to remain fairly hands-off in favor of allowing the students to work
through this process.
Groups compare their results with others who were assigned a different daily use
estimate, reflecting on how the payback period is affected by how long the lights are
on. This step is explicitly written into ESM-A to facilitate compliance (p. 8).
Students answer follow-up questions and draw conclusions as to whether or not
more efficient lighting is economically sustainable (p. 8).
3. Environmental Analysis (10-15 min)
This analysis helps students make connections between the light switch that is flipped on
and the power plant that supplies the electricity (p. 9). By converting electricity use into
mass of CO2, students quantify and compare an environmental impact across two scenarios
of efficient and inefficient lighting.
i.
Groups remain unchanged and use the same daily use estimate (6, 10, or 14 hours)
assigned to them in the economic analysis.
ii.
This analysis requires a conversion factor for mass of CO2 per kilowatt-hour of
electricity. For information about obtaining this value, see the Instructor
Preparation & Materials section.
iii.
Students calculate the annual reduction in CO2 emissions from the lighting project.
iv.
Groups compare their result with others who were assigned a different daily use
estimate, exploring how CO2 emissions are affected by lighting preferences and
behaviors.
v.
Students respond to follow-up questions and evaluate whether more efficient lighting
is environmentally sustainable (p. 10).
4. Societal Analysis and Reflection on the Triple Bottom Line (10-15 min)
This analysis reflects on the societal impacts of the lighting project, asking students to think
about how efficient lighting can improve the well-being of communities (p. 11).
i.
The handout challenges students to come up with at least one example of societal
impacts for each of two different scales (ESM-B provides examples):
a. The narrower-in-scope and immediate impacts relate to how the lighting
project will affect the building and its inhabitants (faculty, students, and
staff).
b. The broader, long-term impacts relate to how efficient lighting will affect
public health and societal well-being, including impacts at local/regional
(better air quality and associated health and economic benefits) and global
scales (climate change mitigation through reduced greenhouse gas
emissions).
page 14
ii.
Students conclude the activity by aggregating their findings into a brief summary of
the sustainability of the lighting project (p. 11). This summary should include an
analysis of each aspect of the triple bottom line and should argue whether or not the
project is a “win” for overall sustainability. If time is short, this final task may be a
homework assignment. See Follow-up Engagement for more details.
5. Conclusion (10-15 min)
i.
Ask groups to discuss with the class their main findings for the economic,
environmental and societal analyses above.
 What are their most significant takeaways from the activity?
 Did the activity affect their views about efficient lighting in particular or
energy use in general?
ii.
Instructors should prompt students to reflect on how the estimates of daily lighting
use influenced both the payback period of the project and the annual reduction in
CO2 emissions. Display student results on the board for comparison. Do they
consider this influence to be significant?
iii.
Ask students to volunteer their opinion on the sustainability of the lighting project.
Push students to justify their opinion from each aspect of the triple bottom line, and
tease out differing opinions if they exist.
iv.
Instructors who wish to extend the discussion may refer to the list of questions
provided in ESM-B.
page 15
Gathering Evidence – Economic Health
Calculating the Payback Period
Why are we doing this?


to apply the Triple Bottom Line to lighting decisions on campus
to recognize scenarios where more efficient lighting may be worth the expense
Let’s shed some light on the economics of this decision. Table 1 provides data for the halogen
lamp formerly used at the Marquee and the new LED lamp.3
Halogen
Cost
(per bulb)
$8.37
Lifetime
(hours)
3,000
LED
$46.85
45,000
Light source
Watts
75
13
Daily use
(hours)
Labor cost to install
(per bulb)
6, 10, or 14
$25
Table 1 – Comparison of a halogen and an LED bulb
We provide 3 possible daily use values: low (6 h/day), average (10 h/day), and high (14 h/day).
Your group will be assigned one of these values. You will compare your results later on to better
understand how the daily use of the lights at the Marquee affects the payback period.
Follow the steps below to calculate the payback period for the Marquee lighting switch. For each
step, enter your results in the blanks next to the corresponding number on the Data Sheet.
1. Form a team of 3. Enter your assigned value for the daily lighting use of the Marquee on
your Data Sheet.
2. Calculate the cost to purchase and install the 11 stage lights:
a. If the lights are halogens.
b. If the lights are LEDs.
3. Find the difference between 2(a) and 2(b). This is the initial extra cost of switching to
LEDs. The payback period will be the amount of time it takes to recoup this investment.
4. Calculate the monthly energy requirements in kW-h of using each type of light.4 For our
purposes, one month will be 30 days.
5. Convert your answers from Step 4 into monthly energy costs for each type of light. Use a
value of $0.11/kW-h for your conversions.5
6. Calculate how many days it will take for both the halogen and LED bulbs to burn out and
need to be replaced. Convert days to months and round to the nearest month.
7. You now have all the data you need to calculate the payback period. It is up to your group
to figure out how to do this. Your payback period should be given in months. If you run
into trouble, ask your instructor.6
page 16
Gathering Evidence – Economic Health
Calculating the Payback Period
DATA SHEET
1. Hours of daily lighting use at the Marquee: 6 hours/day
2. Cost to purchase and install the 11 lights.
a. halogen bulbs:
(11 × $8.37) + (11 × $25) = $367
b. LEDs:
(11 × $46.85) + (11 × $25) = $790
3. Initial cost of switching to LEDs:
$790 - $367 = $423
4. Monthly energy requirements.
a. halogen bulbs:
(11 bulbs) × (75-W/bulb) × (6 h/day) × (30 days/mo) × (1 kW/1,000 W)
= 150 kW-h/mo
b. LEDs:
(11 bulbs) × (13-W/bulb) × (6 h/day) × (30 days/mo) × (1 kW/1,000 W)
= 26 kW-h/mo
5. Monthly energy costs.
a. halogen bulbs:
(150 kW-h/m) × ($0.11/kW-h) = $16/mo
b. LEDs:
(26 kW-h/m) × ($0.11/kW-h) = $3/mo
page 17
Gathering Evidence – Economic Health
Calculating the Payback Period
DATA SHEET
6. Number of months to replace bulbs:
a. halogen bulbs:
(3,000 hours) / (6 hours/day) = 500 days
(500 days) / (30 days/month) = 17 months
b. LEDs:
(45,000 hours) / (6 hours/day) = 7,500 days
(7,500 days) / (30 days/month) = 250 months
7. Calculating the payback period:7
The monthly energy savings is $13.
Each time the halogens need to be replaced costs another $367.
$367 every 17 months equates to $22 per month of avoided costs if the LEDs
were installed instead.
Total LED monthly savings are $13 + $22 = $35/month.
Initial cost of switching was $423.
($423) / ($35/month) = 12 months to recoup initial investment*
*This is the theoretical payback period, because in reality the cost to replace
the halogen lights is not a monthly cost. Bulbs will be replaced when they
burn out and not all at once.
8If
this calculation is made without accounting for the theoretical monthly
cost of replacing the halogen lights, then the payback period will be based
solely on monthly energy savings. This changes the payback period to
($423)/($13/month), or 32 months.
Final value for payback period:
12 months
page 18
Gathering Evidence – Economic Health
Calculating the Payback Period
DATA SHEET
1. Hours of daily lighting use at the Marquee: 10 hours/day
2. Cost to purchase and install the 11 lights.
a. halogen bulbs:
(11 × $8.37) + (11 × $25) = $367
b. LEDs:
(11 × $46.85) + (11 × $25) = $790
3. Initial cost of switching to LEDs:
$790.35 - $367.07 = $423
4. Monthly energy requirements.
a. halogen bulbs:
(11 bulbs) × (75 W/bulb) × (10 h/day) × (30 days/mo) × (1 kW/1,000 W)
= 247 kW-h/mo
b. LEDs:
(11 bulbs) × (13 W/bulb) × (10 h/day) × (30 days/mo) × (1 kW/1,000 W)
= 43 kW-h/mo
5. Monthly energy costs.
a. halogen bulbs:
(247 kW-h/m) × ($0.11/kW-h) = $27/mo
b. LEDs:
(43 kW-h/m) × ($0.11/kW-h) = $5/mo
page 20
Gathering Evidence – Economic Health
Calculating the Payback Period
DATA SHEET
6. Number of months to replace bulbs:
a. halogen bulbs:
(3,000 hours) / (10 hours/day) = 300 days
(300 days) / (30 days/month) = 10 months
b. LEDs:
(45,000 hours) / (10 hours/day) = 4,500 days
(4,500 days) / (30 days/month) = 150 months
7. Calculating the payback period:7
Monthly energy savings are $22.
Each time the halogens need to be replaced costs another $367.
$367 every 10 months equates to $37 per month of avoided costs if the LEDs
were installed instead.
Total LED monthly savings are $22 + $37 = $59/month.
Initial cost of switching was $423.
($423) / ($59/m) = 7 months to recoup initial investment*
*This is the theoretical payback period, because in reality the cost to replace
the halogen lights is not a monthly cost. Bulbs will be replaced when they
burn out and not all at once.
8If
this calculation is made without accounting for the theoretical monthly
cost of replacing the halogen lights, then the payback period will be based
solely on month energy savings. This changes the payback period to
($423)/($22/month), or 19 months.
Final value for payback period:
7 months
page 21
Gathering Evidence – Economic Health
Calculating the Payback Period
DATA SHEET
1. Hours of daily lighting use at the Marquee: 14 hours/day
2. Cost to purchase and install the 11 lights.
a. halogen bulbs:
(11 × $8.37) + (11 × $25) = $367
b. LEDs:
(11 × $46.85) + (11 × $25) = $790
3. Initial cost of switching to LEDs:
$790.35 - $367.07 = $423
4. Monthly energy requirements.
a. halogen bulbs:
(11 bulbs) × (75 W/bulb) × (14 h/day) × (30 days/mo) × (1 kW/1,000 W)
= 346 kW-h/mo
b. LEDs:
(11 bulbs) × (13 W/bulb) × (14 h/day) × (30 days/mo) × (1 kW/1,000 W)
= 60 kW-h/mo
5. Monthly energy costs.
a. halogen bulbs:
(346 kW-h/m) × ($0.11/kW-h) = $38/mo
b. LEDs:
(60 kW-h/m) × ($0.11/kW-h) = $7/mo
page 22
Gathering Evidence – Economic Health
Calculating the Payback Period
DATA SHEET
6. Number of months to replace bulbs:
a. halogen bulbs:
(3,000 hours) / (14 hours/day) = 215 days
(215 days) / (30 days/month) = 7 months
b. LEDs:
(45,000 hours) / (14 hours/day) = 3,215 days
(3,215 days) / (30 days/month) = 107 months
7. Calculating the payback period:7
Monthly energy savings are $31.
Each time the halogens need to be replaced costs another $367.
$367 every 7 months equates to $52 per month of avoided costs if the LEDs
were installed instead.
Total LED monthly savings are $31 + $52 = $83/month
Initial cost of switching was $423
($423) / ($83/m) = 5 months to recoup initial investment*
*This is the theoretical payback period, because in reality the cost to replace
the halogen lights is not a monthly cost. Bulbs will be replaced when they
burn out and not all at once.
8If
this calculation is made without accounting for the theoretical monthly
cost of replacing the halogen lights, then the payback period will be based
solely on month energy savings. This changes the payback period to
($423)/($31/month), or 14 months.
Final value for payback period:
5 months
page 23
Analyzing and Interpreting Evidence – Economic Health
Calculating the Payback Period
1. Confer with teams who used a different value for the daily use of the LED stage lights at
the Marquee. Does the daily usage have a significant effect on the payback period?
______ yes
_____no
Provide values to justify your answer.
Yes. Payback period varies from 5 months – 12 months.
(14 months – 32 months for the alternate calculation of the payback period)
2. Using your value for daily usage, Union South would be expected to replace the LED
stage lights in approximately ____________ (give month) of the year ________.
Show calculation.
July 2013 installation plus 250 months = May 2034
July 2013 installation plus 150 months = January 2026
July 2013 installation plus 107 months = June 2022
3. Union South would have to replace a halogen bulb _____ times before an LED would be
expected to burn out.
Show calculation:
(45,000 months LED) / (3,000 months halogen) = 15 replacements
4. The total amount of savings Union South will enjoy using the eleven LED stage lights
before they burn out is expected to be ___________________.
Show calculation:
($35/mo) × (250 months) = $8,750 total
($59/mo) × (150 months) = $8,850 total
($83/mo) × (107 months) = $8,881 total
*Notice that the savings are similar regardless of daily usage.
5. Is switching to LED lights at the Union South Marquee economically a good decision?
______ yes
_____no
Answers specific to student response, but answer is likely to be YES – look
how much money you would save!
page 24
Gathering Evidence – Environmental Health
Accounting for CO2 Emissions
Now let’s calculate the CO2 emissions at the local power plant as a result of using the lights.
Using your energy calculations from Part 1, determine the monthly CO2 emissions from using
the halogen and LED lights.
Note: Union South is powered by Madison Gas & Electric, which in turn is part of a larger
energy grid in the Midwest. In 2015, this grid emitted 1.61 pounds of CO2 per kW-h.5 Use this
value to determine the CO2 emissions.9
2. Monthly CO2 emissions:
Halogen bulbs
Answer: ________ pounds of CO2 per month per 11 halogen bulbs.
Show calculation:
(150 kW-h/mo) × (1.61 lb CO2/kW-h) = 241 lb CO2 per month
(247 kW-h/mo) × (1.61 lb CO2/kW-h) = 398 lb CO2 per month
(346 kW-h/mo) × (1.61 lb CO2/kW-h) = 557 lb CO2 per month
LED bulbs
Answer: _________ pounds of CO2 per month per 11 LED bulbs.
Show calculation:
(26 kW-h/mo) × (1.61 lb CO2/kW-h) = 42 lb CO2 per month
(43 kW-h/mo) × (1.61 lb CO2/kW-h) = 69 lb CO2 per month
(60 kW-h/mo) × (1.61 lb CO2/kW-h) = 97 lb CO2 per month
5
Value obtained from the U.S. EPA: http://www.epa.gov/egrid.
page 25
Analyzing and Interpreting Evidence – Environmental Health
Accounting for CO2 Emissions
1. For the daily use value assigned to your team, determine the CO2 emissions avoided per
year by swapping the halogen bulbs for LEDs.
241 lb CO2/mo (halogen) – 42 lb CO2/mo (LED) = 199 lb CO2/month
(199 lb CO2 saved/mo) × (12 mo/yr)
= 2,388 lb CO2 saved per year
398 lb CO2/mo (halogen) – 69 lb CO2/mo (LED) = 329 lb CO2/month
(329 lb CO2 saved/mo) × (12 mo/yr)
= 3,948 lb CO2 saved per year
557 lb CO2/mo (halogen) – 97 lb CO2/mo (LED) = 460 lb CO2/month
(460 lb CO2 saved/m0) × (12 mo/yr)
= 5,520 lb CO2 saved per year
2. Calculate the total CO2 emissions (in pounds) that Union South will save over one full
lifetime of the LED bulbs.
(199 lb CO2 saved/mo) × (250 months) = 48,750 lb CO2 saved
(329 lb CO2 saved/mo) × (150 months) = 49,350 lb CO2 saved
(460 lb CO2 saved/mo) × (107 months) = 49,220 lb CO2 saved
*Again, the savings should be similar regardless of usage.
3. Do you think that switching to LED lights at the Union South Marquee is an
environmentally sustainable decision? Explain your answer.
Answers specific to student response, but answer is likely to be YES – look
how much carbon dioxide you would save!
page 26
Reflecting on the Investigation
Connecting the Triple Bottom Line
1. We have yet to address the third component of the Triple Bottom Line: the community.
From a local standpoint, switching the Marquee lights to LEDs is a safety precaution for
the custodial staff. Explain how this can be considered a positive societal impact.
Better health and safety of the workers could mean better staff morale and
less societal costs due to reduced instances of injury.
2. Thinking more about the big picture, how does switching to more efficient lighting
impact communities and societal health?
Reduced emissions and pollutants would mean better air quality, better
overall health of the community, money saved on reduced health issues, and
benefits to local plant and wildlife.
3. Drawing on the information from this activity, analyze the Marquee lighting switch in
terms of its sustainability. Outline your points below, connecting them to the elements of
the Triple Bottom Line. Finally, make a recommendation – should Union South move
forward with this lighting switch?
This is a sustainable move from every angle you look at it. It would save the
university almost $9,000 over the lifetime of just 11 LED bulbs. The reduced
energy demands would save nearly 50,000 lb of CO2 over the lifetime of the
bulbs, and society benefits from safer, happier custodial staff and cleaner
air. It’s a win all around!
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Supplementary Material C: Introduction to Power and Energy
This discussion of power and energy may prove to be helpful in preparation for the activity.
Power refers to the rate at which energy is generated or consumed. It’s an expression of
energy per unit time and can be measured in several different units. One is the joule per
second (J/s). This power unit clearly conveys the idea of energy use in joules over a
period of time in seconds.
The watt (W), equivalent to a joule per second, is another way of saying the same thing.
1 W = 1 J/s
Notice that there is no such thing as “watts per second” or “W/s.” Why? The term watts
already includes the unit of time; namely, a joule per second. Power ratings of household
appliances, like light bulbs, are given in watts, so that’s what we’ll use in this activity. A
light bulb with a power rating of 60 watts means that every second the light is turned on,
60 watt-seconds of energy is being used.
Have you ever closely examined a fluorescent light bulb? It should be marked with its
power rating in watts (W). For example, below is a photo of a 28-watt T-8 fluorescent
bulb that shows its power rating. This is a more efficient tube that replaced the T-12 with
a power rating of 40-W.
Photo by Tim Lindstrom
Fluorescent lights are more efficient than
incandescent lights. This means they use less
power to emit the same amount of light. Compact
fluorescent lights (CFLs), with their notorious corkscrew shape, are
approximately four times more efficient than incandescent lights. In other words, a 25-W
CFL is just as bright as a 100-W incandescent.
Light emitting diodes (LEDs) take efficiency one step farther than CFLs. These bulbs are
typically five-to-six times more efficient than incandescent lights. This may not seem like
a big deal just yet, but CFLs and LEDs represent enormous potential to save energy!
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Energy can be used to perform a task; that is, to “do work.” With light bulbs, the task is
to generate light. Just like power, energy is measured in several units. These include
joules, calories, British thermal units (Btu), kilowatt-hours (kW-h), and watt-seconds
(W-s).
Electricity bills from the local utility are not measured in watts (power). Rather,
electricity bills show energy use, typically in the unit of kilowatt-hours.
Energy is an expression of how much power is being used and how long it was used for.
In other words, energy is power multiplied by time.
energy = power × time
Consider a 32-watt high efficiency fluorescent light bulb. If this bulb is on for 10 seconds,
then 32 watts of power is used every second for each of the 10 seconds. To calculate the
energy expended, multiply power by time.
32 W × 10 s = 320 W-s
Notice that one of the older 40-watt light bulbs would use more energy if it were
operated for 10 seconds.
40 W × 10 s = 400 W-s
We hope that this helps you understand the rationale for replacing 40-W bulbs with ones
rated at 32-W that gave the same amount of light.
Connecting power and energy
An analogy may help you to understand the relationship between power and energy. Let’s say
you’re at a tailgate before a football game, hanging with your friends and drinking ice cold 12-oz
cans of a favorite thirst quenching beverage. One of your friends is slowly sipping, and over time
the liquid inside is slowly leaving the can. Another friend decides to gulp down the contents of
the can, and the liquid quickly rushes out. Each finishes their beverage, but one friend finishes
the beverage much faster. Compare the flow rates of the liquid. From one can, the flow rate is
page 29
low while from the other it is high. The flow rate is akin to power, the rate at which energy is
being used. Although the two friends drank at different rates, in the end they consumed the
same amount.
A 10-watt light bulb is analogous to the person who sips, whereas a 100-watt light bulb more
resembles the one who drank quickly.
A 100-watt bulb running for 2 seconds consumes the same amount of energy as a 10-watt bulb
running for 20 seconds. Just like the two friends, the amount consumed (energy) may be the
same, but the rate of consumption (power) and the time spent consuming are different.
Converting between units of power and units of energy
In order to figure out the energy cost of daily activities, you may need to be able to convert
between units. Even to pros, unit conversions are a pain! It requires careful attention to decimal
points … and practice.
Watts and kilowatts
Watts and kilowatts obey the same rules as other metric units. The prefix kilo means 1000:
1 kilometer = 1000 meters
1 kilowatt = 1000 watts
Here is the conversion factor (or its reciprocal):
Watts, kilowatts, and joules
Both kilowatt-hours and joules are units of energy.
In contrast, the watt is a unit of power. Here is the relationship:
1 watt = 1 J/s (one joule per second) and 1 kW = 1 kJ/s
From this, you can derive the conversion factor between kW-h and kilojoules. Note that we’ve
abbreviated seconds as both “s” and “sec.” Both are in use.
Or more simply:
1 kW-h = 3600 kJ
= 3,600,000 J
And the reciprocal: 1 joule = 2.78 ×10-7 kW-h (a joule is very small!)
page 30
Practice Problems
1. What do these abbreviations stand for?
kW-h
W-s
LED
CFL
Btu
You also may see W-s and kW-h written as W∙s and kW∙h. Both are fine.
So is kWh, although technically it is not correct because it needs a hyphen.
2. Recognize which units are a measure of energy and which are a measure of power. For
example, which of these are units of energy and which are units of power?
watt
kilowatt-hour
Joule
W-s
Btu
calorie
kilowatt
3. Practice converting units of power.
Convert 12,500 watts into kilowatts. Now convert 0.120 kilowatts into watts.
4. Show how to convert from kilowatt-hours to watt-seconds.
For example, 3 kW-h is equivalent to how many W-s?
5. A watt-second is roughly the energy required for one heartbeat. What energy unit is
equivalent to a watt-second?
6. Why is there no such unit as a watt per second (W/s)?
7. Fluorescent lights require about _________ power in watts as incandescent bulbs.
the same ¼ of the 1/10 of the 1/100 of the
8. The energy used by a light bulb in an hour can be calculated from the value of watts
stamped on the bulb. Explain how.
9. Let’s assume that the carbon dioxide emissions per unit energy of power plants in the
United States is 0.66 kg CO2 per kilowatt-hour.
a. How much CO2 would a 100-watt incandescent bulb used for 3 hours per day
emit in one year?
b. How much CO2 would an equivalent 25-watt fluorescent bulb used for 3 hours
per day emit in one year?
c. How much CO2 would an equivalent 17-watt LED bulb used for 3 hours per day
emit in one year?
page 31
Supplementary Material D: Introductory Practice Problems
These practice problems may be helpful as preparation for the in-class activity.
Lighting Facts Labels
Photos by Tim Lindstrom
1. Cost to purchase the bulb
a. Before you calculate anything – take a guess. Which do you think costs more to
buy, an incandescent bulb or a compact fluorescent bulb?
b. As of 2014, a pack of five 60-W incandescent bulbs cost $5.88 at Home Depot.
What is the price per bulb?
c. As of 2014, a pack of five 14-W compact fluorescent bulbs cost $37.81 from
Walmart. What is the price per bulb?
d. Verify the prices by a web search. Do you find comparable values?
2. Cost of bulb over time (bulbs burn out!)
a. Examine the Lighting Facts labels. Which bulb lasts longer?
b. How many incandescent bulbs would you need to purchase over the lifetime of
the fluorescent bulb?
3. Energy cost over bulb lifetime (you have to pay the electric bill!)
a. For the compact fluorescent bulb shown above, calculate the energy cost over its
lifetime. Use the information on the Lighting Facts label.
b. Do the same thing for the incandescent bulb.
4. OK, let’s put this all together. Fluorescents cost more at the store. But they last longer. Do
they really cost more over the lifetime of the bulb? Let’s do the math using 2012 prices: the
cost to purchase an incandescent bulb was $1.50 and a CFL was $9.99.
page 32
Calculate the total energy cost to use each bulb over the lifespan of a CFL. You will need to
include the cost of each bulb (+ additional incandescent bulbs after the original burns out).
5. What about the emissions that come from the electricity used to power the bulbs? Calculate
the CO2 emissions of each bulb over the lifespan of a CFL (5.5 years @ 3 hrs/day).
a. First, determine the total energy use of each bulb over this time.
b. Then, calculate the emissions. The carbon intensity of electricity in the United
States is approximately 0.66 kg CO2 per kilowatt-hour.
6. Calculate the total mercury (Hg) emissions of each bulb over the lifespan of a CFL.
Note: assume 0.023 mg Hg is released per kW-h. Also assume a CFL contains 4 mg Hg.
Checking the Claims
On its website selling fluorescent bulbs, Home Depot explains to its customers:
“The amount of light the bulb gives off is measured in lumens, while the power is
rated in watts. Lumens per watt is a way of identifying how many lumens a light
source provides compared to the amount of energy, or wattage, used. Where
incandescent lamps provide 17–20 lumens per watt, a fluorescent lamp delivers as
much as 90 lumens per watt. To choose the most energy efficient bulb, check the
lumens-to-watts ratio on the bulb’s packaging—the greater the lumens-to-watts ratio,
the more energy efficiency the bulb provides.”
Here are the Lighting Facts for a 14-watt compact fluorescent bulb:
a. How closely does this match the top rated CFLs that deliver 90
lumens per watt, as reported by Home Depot?
b. The bulb is billed as a “60-watt equivalent.” Does this bulb match
the general rule that a CFL uses ¼ the power of an incandescent?
c. Verify the calculation on the package that the estimated yearly
energy cost is $1.69.
d. Is the electricity cost of $0.11 per kW-h comparable to that for
residential customers in your area?
e. The package reports “Energy used 14 watts”. Why is that statement
incorrect?
Photos by Cathy Middlecamp
The bulb package notes that the product “Contains Mercury” and gives the URL for the
EPA web site. Visit this web site and report two important steps to take when a CFL breaks.
f.
page 33
INSTRUCTOR ENDNOTES
General Notes for Instructors
1 Have the students spend roughly 5 minutes independently reading the Asking Questions and Preparing
to Investigate sections. When they finish reading, they can answer the pre-activity survey question(s),
responding to the electronic poll and turning in the paper copy. At this point, instructors may begin a brief
discussion with the whole class. For more information about implementation, consult Part 2 of the
Activities section of the book chapter.
2 For more information about the Triple Bottom Line, consult the notes at the beginning of this
document.
Gathering Evidence – Economic and Environmental Health
3 This particular lighting project replaces halogen lights. Halogens are essentially incandescent lights that
are slightly more efficient. Instructors are encouraged to use their own lighting data if possible. In this
case, it may be easiest to use a more traditional incandescent light bulb. Regardless, the authors
recommend presenting the data to students in a format similar to Table 1. Consult the Instructor
Preparation and Materials section of the book chapter for more details about the lighting data.
4 The power rating of light bulbs is given in watts, but electricity costs are measured in kilowatt-hours.
Students will need to add the total wattage of all 11 bulbs, determine the number of hours per month the
bulbs will be on, and multiply power by time to calculate the monthly energy requirements in watt-hours.
Divide the value in watt-hours by 1,000 W/kW to convert the value into kilowatt-hours. Consult the
Power and Energy handout for more information about unit conversions.
5 At the time of writing, the residential cost of electricity in Madison, WI was $0.11 per kilowatt-hour.
Instructors may use their own residential cost of electricity, or consult the facilities staff at their
institution for an even more case-specific rate.
6 Students are encouraged to discover their own method of determining the payback period for this
lighting upgrade. If they run into problems, the method used by the author is described in the next
endnote.
7 Process for determining the payback period:
1) Determine the monthly energy savings.
2) Convert the total cost of replacing all the halogens ($367) into a theoretical monthly cost. To do
this, divide the cost of replacing the halogen lights by their lifetime in months.
3) The theoretical monthly cost to replace the halogens can be thought of as additional monthly
savings for the LEDs because this becomes an avoided cost.
4) Add the monthly energy savings and avoided monthly costs of replacing the halogen lights to
determine the total monthly savings due to installing LED lights.
5) Divide the initial cost of switching to LEDs ($423) by the total monthly savings to determine the
number of months it will take to recoup the investment – this is the payback period.
8 A simpler (but less accurate) method for determining the payback period would be to not account for
the theoretical monthly cost of replacing the halogens. The payback period is then only dependent on
dividing the initial cost of switching by the monthly energy savings. This significantly increases the
payback period.
9 Instructors may reuse this conversion factor for mass of CO2 per kilowatt-hour or use a value more
specific to their locality. Consult the Instructor Preparation and Materials section of the book chapter for
more information about this conversion factor.
page 34
APPENDIX A: RELATION OF THIS ACTIVITY TO SCIENTIFIC LITERATURE
Scientific assessments of campus lighting have been published for more than a decade. A study projecting
economic savings and CO2 emission reductions for a proposed lighting upgrade was performed at the
University of Melbourne (Di Stefano 2000); a study assessing savings for a completed lighting upgrade
was carried out at the University of Malaya (Mahlia et al 2011). Most relevant to this activity, two
undergraduate students performed an economic and environmental analysis of street lights on the
campus of Yale University (Cole & Srivastava 2013).
APPENDIX B: RELATED TEACHING ACTIVITIES AVAILABLE ONLINE
1.
2.
3.
4.
5.
6.
7.
8.
Cambridge Energy Alliance (2011) Activities for energy efficiency: the better bulb. Energy
Activities for Kids. http://cambridgeenergyalliance.org/wp-content/uploads/Energy-efficiencylesson-plans.pdf. Accessed 10 Feb 2015
Colorado State University Extension (2014) Lesson 4: light bulb or heat bulb. Energy Resources –
Energy Curriculum. http://www.ext.colostate.edu/energy/k12/bulb-lesson.pdf. Accessed 10 Feb
2015
Colorado State University Extension (2014) Lesson 6: conduct a school energy audit. Energy
Resources – Energy Curriculum. http://www.ext.colostate.edu/energy/k12/audit-lesson.pdf.
Accessed 10 Feb 2015
Energy Star (2008) Energy efficiency ambassadors. Educate Students.
https://www.energystar.gov/ia/partners/promotions/change_light/downloads/classroom_activi
ty_9_12.pdf?0b55-1475. Accessed 10 Feb 2015
National Renewable Energy Laboratory (2013) Lighting in the library. Education Programs.
http://www.nrel.gov/education/pdfs/educational_resources/high_school/energy_audit_hs.pdf.
Accessed 10 Feb 2015
Peak Student Energy Actions (2014) Add it up & make it count. Teacher’s Corner. (Direct
download)
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=
0CB4QFjAA&url=http%3A%2F%2Fwww.peakstudents.org%2Fcivica%2Ffilebank%2Fblobdload.a
sp%3FBlobID%3D2860&ei=k7J_VPKjCYiNyASzxYCADA&usg=AFQjCNG9fNv4H6KnN6MWViP0NjNAJTvLw&sig2=SJwj8JF7C8U29AnJuhcu-w&bvm=bv.80642063,d.aWw.
Accessed 10 Feb 2015
Peak Student Energy Actions (2014) Unit 6 PEAK student energy action activity: lighting survey.
Teacher’s Corner. (Direct download)
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=
0CB4QFjAA&url=http%3A%2F%2Fwww.peakstudents.org%2Fcivica%2Ffilebank%2Fblobdload.a
sp%3FBlobID%3D2949&ei=b7R_VOXYItG2yAS-1IK4Bg&usg=AFQjCNG550VwqgYcbAvgRSKIHdqVflx0g&sig2=a6lucp36vdYfr7QZ8vOcng&bvm=bv.80642063,d.aWw. Accessed 10 Feb
2015
U S DOE Energy Efficiency & Renewable Energy (2014) Comparing light bulbs. Energy Education
and Workforce Development.
http://www1.eere.energy.gov/education/pdfs/efficiency_comparinglightbulbs.pdf. Accessed 10
Feb 2015
page 35
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2.
3.
4.
5.
6.
7.
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9.
10.
11.
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13.
14.
Board of Regents of the University of Wisconsin System (2014) Understanding sustainability and
the triple bottom line. University of Wisconsin Sustainable Management.
http://sustain.wisconsin.edu/about-sustainable-management/. Accessed 17 Mar 2015
Cole C and Srivastava C (2013) Energy blitz leads to measured reductions on campus: students
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Di Stefano J (2000) Energy efficiency and the environment: the potential for energy efficient
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Energy Star (2014) Learn about CFLs. Energy Star.
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