Incandescent  vs.  Fluorescent  Bulbs 
Question: Is the energy use the same for bulbs turned on and off after each use equal to continual use? For years there has been a controversy about the energy savings associated with turning off light when leaving a room. Is there a time, under which, there is no savings?
Study Focus: This lesson will attempt to debunk the belief that lights, especially fluorescent, should be left on to preserve energy.
Skills: Computing, Graphing, Analyzing
Objectives: After completing the activity, students will be able to:
Observe, record, and interpret data.
Use charts, tables, and graphs.
Identify how energy is measured, and read a Watt-rate meter.
Communicate ways that changes in behaviors can affect energy consumption.

OR Science Standards

Benchmark 3
The Dynamic Earth
Forming the Question

The Dynamic Earth
Forming the Question

Watt-Rate meter

Light sources
There is an on going belief that lights are more efficient if they are left on rather than being turned off each time they are not in use. This lesson will give students a start at collecting data to support or refute this belief. This URL is a place to start a web search to study this question. (New fluorescent bulbs require little extra energy to start. )

1. Divide the class into four groups. Two groups will experiment with five incandescent bulbs each while the other two use five fluorescent bulbs each. The groups will use the their Watt-rate meters to measure the energy used in 30 minutes

Incandescent bulbs One group will use the Watt-rate meter to measure for 30 continuous minutes. The other group will be turning the lights on and off 30 times. This group must carefully measure the total time the bulbs are actually on and stop when the meter has been running for a total of 30 minutes.
Fluorescent bulbs These two groups will follow the identical procedure used bythe Incandescent bulb group.

It may be difficult to control all aspects of this study so be sure to clearly discuss the limitations of each experimental design with your students.

2. Compare the results for the four trials.
a) Did the groups get similar numbers when comparing incandescent to incandescent and fluorescent to fluorescent?
b) Do these numbers suggest efficiencies to be gained by turning lights off when not in use—no matter the time the lights are off?
c) Do these numbers lead to different experimental designs?