Light Intensity

Home Light Intensity Light Angle Activity Earth-Sun Distance

Probing Questions:

What relationship is there between the amount of light a source gives out and the distance from the light source?  If you place a lamp twice as far away as it was, how much light will you receive?  What is the relationship between a light bulb's wattage and the amount of light (lumens) that it gives off?  This activity will help you investigate the relationship between the distance from the light source and the amount of light received.

Materials:

  • Light source such as 60 or 75 watt bulb.

  • TIŽ Graphing Calculator

  • CBLŽ or CBL2Ž with light probe

  • Meter stick

  • ExcelŽ spreadsheet (optional)

  • MathematicaŽ modeling software (optional)

Procedure:

  1. Set up the CBLŽ and light probe with the TIŽ Graphing calculator according to the instructions that came with the CBLŽ.

  2. Position the light probe next to the meter stick so that it is 50 cm away from the light source. 

  3. Run the CBLŽ program to collect the light intensity at the following distances:  50 cm, 60 cm, 70 cm, 80 cm, 90 cm, and 100 cm. 

  4. Record the values of the light intensity in an ExcelŽ spreadsheet.

  5. Graph the data and print the results.

  6. Calculate a power regression for the data.

  7. Predict what the light intensity would be for a distance of 125 cm and for 160 cm. 

  8. Run the data collection for the predicted distances of 125 and 160 cm.

Results:

  1. What is the relationship between the light intensity and the distance of the light source?

  2. What was your predicted light intensity for 125 and 160 cm?

  3. Was your prediction close to the actual light intensity data?  Why or why not?

  4. What would cause any discrepancy in your predicted and collected data.

  5. Write an equation showing the relationship between light intensity and distance from light source.

  6. Does the light intensity change for the surface of the earth during its revolution around the sun?  Why or why not?

  7. What effect would any change in the light intensity have on the earth's systems?  Name as many as you can.

Extension:

  • Gather data for another planet in our solar system.  Predict what the light intensity would be for the surface of the planet.

  • Does the surface temperature of the planet correspond to the distance to the sun?  Why or why not?

  • Using MathematicaŽ plot your data for your experiment.  Experiment with different types of plots or graphs to view the data.

Graph Results:

Click here to see examples of graphs of light intensity vs distance.