Light's Out! Comparing Energy Use

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SWBAT make a claim from evidence collected on the electrical efficiency of different light bulbs.

Big Idea

Students compare and contrast the electrical output of LED, CFL and incandescent light bulbs.

Getting Started

In this activity, students compare several qualitative and quantitative measurements of three different types of light bulbs, CFL, incandescent and LED. This lesson connects with the previous lesson on energy audits part one and the lesson that follows this, Energy Audits (Part Two), where students are asked to evaluate their individual energy use and evaluate their household energy use by looking at their utility bills. The goal being for students to make more informed choices and recommendations on the types and sources of devices used in their home that might eventually lead to a reduction in the electrical use for their household, thereby saving resources.


Create at least one station for each bulb if possible.

  • A lamp (I have a class set of the triangular bases shown below).
  • 3 kinds of light bulbs (keep boxes/packaging for other questions).
    • 1 – Incandescent 100W bulb
    • 1 – Compact Fluorescent 100W equivalent bulb
    • 1 - LED 100W equivalent bulb (you can find these for around $7.00 ea at
  • Infrared thermometer (gun) (available at
  • Kill-A-Watt Meter (available at
  • Science journals OR teacher made data table*

 I suggest that if your students aren't accustomed to reasoning about how to best organize and display their data, this might be a good lesson to start that practice. Some guiding questions to help students think it through are:

  •  What variables will you test?
  •  what measurements will you take for each test? 


10 minutes

Show the class the three light bulbs and ask students what they know about their similarities and differences.  

If you are not familiar with the science behind these three types of lightbulbs., the state of California has an Incandescent, LED, Fluorescent, Compact Fluorescent and Halogen Bulbs website with some background reading for you and your students. 

I suggest printing copies of the reading and giving students the few minutes to read through the text. As they read  asked them to write down information from the reading that addresses the differences (pros/cons between incandescent, LED, and compact fluorescent light bulbs. 

Create a three column table, labeling each column for one of the light bulbs and record their ideas. 


30 minutes

Students complete Lights Out, an experiment on energy efficiency. All bulbs must be of the same equivalency to work. Note, a 100W equivalency really means that a bulb gives off the same light. (Measured in Lumens, a 100W bulb gives off approximately 1600 Lumens). Each student should create a table in their journals that compares the bulbs for the following categories:

  • Purchase price
  • Electricity usage (watts)
  • Lumens (estimate or may be found on packaging)
  • “Efficiency” (lumens/watt)
  • Temperature of bulb after 5 minutes
  • Apparent color of bulb
  • Observations/Notes
  • Lifespan of bulb (found on packaging)
  • Bulb cost over bulb’s lifetime (price/lifespan)
  • Bulb cost over 10 years (assume you run it for 6 hours a day and will purchase multiple bulbs)
  • Energy cost of running the lamp for each bulb for 6hr/day for 10 years (check your electricity bill for the price of a kWhr) 

To save time, I created a Student Data Sheet

Once students have collected the data, they write a claim using this evidence to compare the energy efficiency of the three bulbs types. 



15 minutes

After collecting data, students summarize their findings using these guiding questions: 

  1. For the bulbs that were less efficient, where did the energy go?  Explain in your own words.
  2. Which bulb do you think is the best-selling?  Why?
  3. Which bulb is the best for the environment?  Please think about the entire lifecycle of the bulb.  (This is a question that may require some research.)
  4. Based on your observations, which bulb do you recommend? Why?
  5. After doing this exercise, what is something that surprised you (or something you did not know before?)


5 minutes

One of the purposes of this lesson is to have students make a claim based on evidence. You will want to have a way to measure their writing. I have attached a basic Claims, Evidence, Reasoning Rubric for you to use. If you already have a rubric in place, feel free to substitute yours. This rubric is based on the work of Kate McNeil of Boston College. You can read more about her work and assessment of student thinking in science, by reading her book, Supporting Grade 5-8 Students in Constructing Explanations in Science: The Claim, Evidence, and Reasoning Framework for Talk and Writing.

 In the video below one of my students  reflects on using data from this lab activity to make his claim on the efficiency of lightbulbs.