November, 2002, Biology Experiment:

Let There Be Light

- Purpose
- Background Information
- Equipment & Supplies
- Software & Probeware Set-up
- Experimental Procedure
- Data Analysis
- Conclusions and Extensions


PASPORT Light Sensor
(PS-2106)

ScienceWorkshop Light Sensor
(CI-6504A)

Purpose:

Students will use a Light Sensor to investigate the level of light intensity over a 24-hour period. They will also identify potential factors if unexpected results are observed.

 

Background Information:

Life on earth, no matter what form it assumes, depends ultimately on sunlight.

Whether on land or in the water, green plants use chlorophyll and energy from the sun to turn carbon dioxide, water and inorganic salts into complex organic materials -- mainly carbohydrates and proteins.

This process, called photosynthesis, produces oxygen as a by-product. Photosynthesis is the foundation of all food chains. It's the basic building block for life on earth. In one way or another, animals are dependent on plants for nutrition. As they breathe, animals take in oxygen and give off carbon dioxide. Plants, in turn, use the carbon dioxide in photosynthesis, and the cycle goes on.

The most popular scale for light measurement or luminous intensity is measured and reported in Lux. A light meter is sometimes referred to as a Lux meter. One Lux is equal to the total intensity of light that falls on a one-square-meter surface that is one meter away from the point source of the light.

1 Lux = 1 lumens /sq. meter

Hypothesize: At what points of the day will light intensity level be the highest? The lowest?

Back to top

Equipment & Supplies:

For each lab group:

Back to top

Software & Probeware Set-up:

  1. Ensure that your USB Link, Xplorer or ScienceWorkshop 500 interface is connected to the computer.

  2. Click on one of the links below to download a pre-configured DataStudio file for this experiment, and then open the file.

    PASPORT users: PS Windows (.zip file) or PS Macintosh (.sit file)
    ScienceWorkshop 500 users: SW Windows (.zip file) or SW Macintosh (.sit file)

    When the file is opened, you should see a Graph Display of Light (lux) vs. Time, as well as a Digits Display of Light Intensity.

  3. The sample rate has been set to take a measurement once every 5 minutes. You can verify this by clicking the Setup button ( ).

  4. If you are not using the pre-configured DataStudio file, first click the Setup button ( ). The Sample Period default will read "5 Hz." Change it to "5 Minutes" by using the pull-down tab. Click ( ) to close the Experimental Setup window.

  5. Connect the Light Sensor to the Xplorer or USB Link (PASPORT users) or plug the Light Sensor into channel A of the 500 Interface (ScienceWorkshop 500 users).

    If you are using the ScienceWorkshop 500 Interface, be sure the interface is turned on and the Light Sensor is associated correctly in the Experiment Setup window.

  6. Resize and arrange the display as needed.

Experimental Procedure:

Equipment Setup:

  1. Place the Light Sensor and interface near a window, with the top of the sensor pointed up toward the sky.

  2. Select the "Sun" setting on the sensor by pressing the bottom green button.

  3. Note: If your classroom computer is not located near a window, you can remotely use either the Xplorer or the ScienceWorkshop 500 interface. Once your experiment is completed, connect the interface to the computer and download the stored data into DataStudio.

Data Collection & Recording:

  1. Click the Start button ( ) to begin collecting light intensity data. The graph should display the first data point. Every 5 minutes, a new data point should appear.



  2. Click the Stop button ( ) after the 24-hour period has ended.

Back to top

Data Analysis:

  1. Scale the axes to fit the data using the Scale to Fit button ( ) in the Graph toolbar.

  2. Use the Note Tool ( ) to annotate where on the graph environmental conditions changed -- i.e., clear sky, clouds, fog, rain.

  3. Examine the graph and study the data. At what point was the light intensity reading the highest? The lowest?

  4. Use your local newspaper or the Internet to look up the sunrise/sunset times for your city. Annotate these times on your graph. Was there a significant change in light at those times? If not, explain what factors may have contributed to that.

Conclusions and Extensions:

  1. How did the light intensity during different parts of the day correspond to any noted environmental changes?

  2. Explain how the graph may look if data was collected during a storm, or 6 months later during another season.

  3. An ongoing study can be done by performing this activity throughout the school year. Data can then be compared over time.

  4. Determine the average number of daylight hours by month. (See graph below for an example)


Back to top