7. Better Ways to Illuminate
In this module, students compare three types of lamps that are used for lighting: incandescent, compact fluorescent (CFL) and light-emitting diodes (LEDs). Students collect data on the amount of heat and light generated by these bulbs to assess their efficacy, discover how much it costs to operate the bulbs, and calculate the payback period.
Students will be able to:
- Describe the similarities and differences among incandescent, fluorescent, and LED lamps.
- Collect and compare data on the amount of light and/or heat generated by incandescent, fluorescent, and LED lamps.
- Determine the cost differences in operating incandescent, fluorescent and LED lighting and calculate their payback periods.
- Describe factors inhibiting the widespread adoption of compact fluorescent and LED lighting.
Description and Teaching Materials
Student materials for this module are provided at the following link:
The instructor may start the module with a historical overview of lighting and then discuss the different lamps that the students will use and the concept of efficacy (i.e., lumens per watt). From the first course module, you may need to review what a kilowatt is. Introduce the students to the payback period concept and walk through an example of how it is calculated. This may need to be covered with additional examples.
Assign a group of two or three students to a test box where one student reads the thermometer and light meter while the others record data every ten minutes until 40 minutes have passed and then change the bulb type (depending on how long the lab period is you may be able to replicate). Allow a few minutes for the air in the box to reach ambient temperature before changing bulbs.
The materials below are needed to build one test box but you will need at least three boxes, one for each lamp.
- A test box for each bulb (e.g., a box constructed of cardboard). The box should be about 30 x 30 x 25 cm or large enough to hold the bulb, thermometer and light meter.
- A thermometer to measure changes in temperature.
- A light meter to measure changes in light levels.
- A light bulb (i.e., an incandescent, CFL, or LED lamp, each equivalent to a 60-watt bulb).
- A light fixture for plugging in the light.
Structuring Class Time
Quiz & Discussion. This module typically is the seventh for the course and follows the module on Energy from and to Earth. It can also be taught as a stand-alone module, but you may still want to have the students review the material in the first module on Electricity, Work and Power. Begin the class with a quiz from the prior week's module. Have students come to class with quiz questions, and select five students to read their questions aloud. After each student recites her/his question, pause for the appropriate time for their classmates to write answers. After all five questions have been completed, ask five different students how they answered the questions. This format allows focused discussion on the topic. Students have an opportunity to work through their understanding of the material. Also the teacher gets feedback on the effectiveness of teaching materials and teacher delivery—what is clear and what is still muddy. Use the instructor-regulated discussion pedagogy as explained in the course overview for developing discussions of the current module.
It is important to help the students use what they learned in the earlier modules to gain a deeper understanding of this module. As the professor, you can help them apply what they have learned from previous modules, especially from the first module and the module on Creating Electricity from Light to fully grasp efficiencies gained from CFLs and LEDs. This module takes some of those concepts and applies them to newer bulb technology. The opening quiz reinforces the scaffolding of learning and forces students to revisit the previous module twice, once during their studies when they review for the quiz and formulate the quiz questions, and again when they participate in class discussions.
The flipped-classroom structure advocated for this course facilitates the development of metacognition by the students, directly involving them in the learning process. The use of student-generated questions for quiz and discussion helps students become aware of how they learn and understand the material. This is a big departure from the simple memorizing of terms and concepts that characterized much of their earlier education. Having students think of questions for quizzes and discussion will inform their approach to learning in general. Another metacognitive strategy used in the course is requiring the students to apply basic science concepts to understanding a technology, and then requiring them to think about the application of that technology in the real world. In this case, have the students think about why many homes in the United States are not using CFLs or LEDs, whereas in some countries (e.g., Mexico), CFLs are ubiquitous.
A major theme of this course is that students see the various technologies in the context of the global system, and this requires systems-thinking. This module on Better Ways to Illuminate provides an opportunity for students to see how the newer lamp technologies help reduce the amount of energy consumed. This consumption, in turn, can have an effect on overall fossil fuel emissions. Students can think this through and—depending upon the mix of energy generation for their area—they can calculate what the reduction in carbon dioxide emissions would be if everyone in their city switched to CFL or LED bulbs.
Student Presentation. Each class should have one or two PowerPoint presentations by students, given either during the current module or at the beginning of the next module. This activity involves peer instruction. For this module, students could be a mayor or a city council member who might develop incentives for citizens to adopt more efficient bulbs. They could also delve deeper into the payback calculations and examine how changing technology costs and/or energy costs affect the payback period.
Hands-on laboratory work. In this module students track the amount of heat and light emitted by three different lamps to understand their energy efficacy. Spreadsheets Across the Curriculum may be useful to help the students use Excel to do the calculations and present their work.Please see the course overview to see how we suggest that you structure the class.
Teaching Notes and Tips
This module is designed for non-science majors at the undergraduate level enrolled in a laboratory class. It takes about 1.5 to 2 hours to run. It can be used independently from all the other modules, but the instructor will need to go over several concepts covered in the first module (e.g., kWh) (Module 1: Electricity Work Power).
You will need to spend some time on the payback period concept as students will struggle with those calculations (see Payback Period (Excel 66kB Oct29 17)). I suggest discussing how to do the calculations while the students are recording the data from the boxes. Note that there are many methods used to calculate payback periods. Some are very complex, but the one used in this module is simple and allows the students to grasp the concept.
The Payback Period Excel spreadsheet has four tabs at the bottom that take you through collecting the data on the three lamps, a payback period example, calculating annual energy costs of lamp operation and then finding the payback period. You will need to have the students find out how much 1 kWh of energy costs in their area. Also, the costs of the LED and CFL lamps have changed over the years, so those costs need to be updated for your area. The students can change the payback period by changing the costs of the new technology and the costs of a kWh of electricity and think about how these changes affect the payback period, and what it may mean for widespread adoption of newer energy efficient technologies.
The lab could be run without taking light measurements and focus on the temperature differences by purchasing bulbs rated at similar lumens. Using three boxes students can graph the changes in temperature and light levels over time. Students will see clear differences in the amount of heat and light generated between the incandescent lamp compared to the CFL and LED lamps (the lamps used here were all equivalent to a 60 W lamp). The differences between the CFL and LED lamps probably won't be detected because their temperature and light levels are so similar (see Effect of box type (Acrobat (PDF) 580kB Oct29 17)).
Prior to class you may assign the readings in the References and Resources to the students. The paper by Amann et al (2013) has some good technological facts and descriptions regarding the three lamps. Ek and Soderholm (2010) and Reynolds et al (2012) will give students an idea of the obstacles that prevent consumers from acting rationally when it comes to energy efficiency and may provide a basis for discussion when it comes to question three below.
After the students have graphed the results of the laboratory, have them answer the following:
- Discuss the results from the above experiment. Which lamp do you think is the most efficient and why? Rank the lamps in terms of their ratio of light to temperature—how does the best-performing bulb compared to the worst-performing bulb? Which lamp would be best to use in a house in which you were trying to reduce the cost of cooling, and why?
- The cost of using any electrical appliance is its wattage multiplied by the price of electricity multiplied by the amount of time the appliance is used. Find out how much electricity costs for your area then calculate how much it costs to run the bulb for a year if it is on for 5 hours every day. Once you know how much it costs to operate the bulb for a year, determine the payback period for:
a) Replacing an incandescent bulb with a LED.
b) Replacing a CFL with an LED.
- Based on the information you collected in questions one and two, why do you think LEDs and florescent lamps are not more common in households?
Student assessment is based upon three different student activities: student-generated quizzes and discussion, student presentations, and module reports based upon laboratory and other work. In addition, there is a pre/post test that can be used to provide further assessment. The assessment methods for this module can be found on the course assessment page.
References and Resources
- Amann, M.M., G.B.Jasmon, H. Mokhlis and A.H.A. Bakarb (2013) Analysis of the Performance of Domestic Lighting Lamps. Energy Policy 52 (2013) 482-500. This is a good overview of the different lamps but the quality of the writing is lacking.
- The following two papers discuss obstacles that prevent consumers from purchasing energy efficient technologies or behaving in energy efficient ways:
- Ek, Kristina and Patrik Soderholm (2010) The Devil is in the Details: Household Electricity Saving Behavior and the Role of Information. Energy Policy 38 (2010) 1578-1587.
- Reynolds, T., J. Kolodinsky and B. Murray (2012) Consumer Preferences and Willingness to Pay for Compact Fluorescent Lighting: Policy Implications for Energy Efficiency Promotion in Saint Lucia. Energy Policy 41 (2012) 712-722.
- Electricity Work Power module
- Consumer Reports: How to read a lightbulb label, August 13, 2015
- EPA: Cleaning Up a Broken CFL
- EPA Energy Star: Learn about LED bulbs
- EPA Energy Star: Information on Compact Fluorescent Light Bulbs (CFLs) and Mercury
- Lux Magazine: Efficacy Explained, May 2012
- Sciencing: How to calculate efficacy, April 2017
- National Geographic: U.S. Phase-Out of Incandescent Light Bulbs Continues in 2014 with 40-, 60-Watt Varieties, December 2013
- US Department of Energy: Lighting Choices to Save You Money