National Teacher Enhancement Project

## Middle School Home Energy Audit

### LIGHTING DILEMMA EXPERIMENT

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INTRODUCTION

As we have learned, power is a determination of how fast work can be done. This means, that for a certain amount of work, more power means less time to accomplish the task. How well this works for someone using the power really depends on many factors. For example, does the work really need to be done rapidly or could some energy be saved by letting the work happen slower? There is a tradeoff for every increase in the speed of work we do. Sometimes we decide the extra cost in increased power is worth it, and sometimes we find the extra power is unnecessary.

Consider the lighting in a home, school, or office. We all know that sufficient light is needed to work effectively and live comfortably as we go about our daily routine. What is the cost in terms of energy that we pay for different types of lighting? What are the benefits to the lighting options we choose? Are certain types of lighting preferable or more efficient than others?

In this experiment, you will investigate and compare different types of light bulbs with respect to the light given off and the amount of power consumed. The data you collect will help guide a class discussion on energy use. Furthermore, your conclusions relating to energy usage and light production should help you make decisions with respect to your home energy audit and energy conservation ideas.

BACKGROUND INFORMATION

• To refresh your understanding of how energy and power are related, you may want to review the Energy Page and Power Page.
• Electricity travels in circuits. A switch opens and closes the "loop" through which electrons can flow. When a switch is "open," electrons can not flow in a circuit.
• Electrical power is measured in watts.
• A kilowatt-hour (kWh) is equal to 1000 watts of power provided for one hour.
• Light is measured in lumens.

MATERIALS

• Light bulbs of various sizes and types (different wattage ratings, incandescent bulbs, compact fluorescent bulbs, etc.)
• Light socket
• Power meter (measuring watts)
• Light meter (measuring lumens)
• Stopwatch or watch with a second hand
• Metric ruler

HYPOTHESIS

Make a hypothesis for the experiment you are about to do.

• Which light bulbs do you think will produce the most light?
• Which light bulbs do you think will use the most power? Which will use the least?

PROCEDURE

SAFETY NOTE: SHOCK HAZARD!!! MAKE CERTAIN BEYOND ALL DOUBT THAT LIGHT SOCKETS AND WIRING ARE SAFE!!!

1. Install the lowest rated light bulb into the light socket. Plug the light socket into a working power outlet. Test the circuit and bulb by turning the light "on." If everything works, turn off the light and proceed to the next step. Consult your teacher if the light does not turn on. Record the type of light bulb and its power rating in your data table.
2. Turn the light bulb on. Hold the light meter exactly 50 cm from the surface of the light bulb. Measure the amount of light coming from the light bulb in lumens using the light meter. Record the results in your data table.
3. Repeat steps #1 and #2 for each of the light bulbs you have selected to test. Be sure to record the correct information in your data table for each bulb.
4. When you have collected data for all of the bulbs, create a bar graph showing the light produced in lumens by each light bulb.

These may be done concurrently with the experiment above or completed separately.

1. Connect the light socket to a power meter. Measure the actual power usage of the light bulb. How does the measured power use compare to the rating on the bulb itself?
2. Use a simple hand-held spectroscope to observe and compare the spectra (different colors of light) produced by different types of bulbs. How does the spectra differ between light bulb types? Does the power rating of the bulb change the spectra? How might this be important?
3. Use a power meter to determine how long particular light bulbs can remain on using only 1 kilowatt-hour of energy. Compare different combinations of number of separate bulbs and bulb power usage to maximize time and amount of light for a room or house. How might this influence lighting decisions in areas of limited power supply?

DATA TABLE

 Create a table like the one below or use the

TABLE 1. Amount of light in lumens produced by different types and powers of light bulbs.

 light bulb Type (incandescent, compact fluorescent, halogen, etc.) Power Rating (Watts) Light Produced (lumens) Rank of light bulb from Lowest to Highest in terms of Light Produced

ANALYSIS QUESTIONS

1. How did the amount of light vary between the light bulbs you tested?
2. What influence does power rating have on the amount of light produced?
3. Which light bulb(s) would provide the most light?
4. Which light bulb(s) would provide light for the longest amount of time using only 1 kilowatt?

CONCLUSION

1. What results did you observe?
2. Were there any trends apparent?
3. What do your results mean in terms of light produced and power used?

Created for the Fermilab LInC program sponsored by Fermi National Accelerator Laboratory Education Office and Friends of Fermilab, and funded by United States Department of Energy, Illinois State Board of Education, North Central Regional Technology in Education Consortium which is operated by North Central Regional Educational Laboratory (NCREL), and the National Science Foundation.

Authors: Sue Emmons, Powell Midddle School, Littleton, CO; Kevin Lindauer, John F. Kennedy High School, Denver, CO; Janet Stellema, Monarch K-8, Louisville, CO; John Sepich, Scott Carpenter Middle School, Westminster, CO; Edited by Marge Bardeen NTEP II Project PI.
Webmaster: ed-webmaster@fnal.gov
Created: September 9, 1998 revised October 2, 2001
URL: http://www-ed.fnal.gov/ntep/f8/projects/nrel_energy_2/lightinglab.html