Costa Rica Rainforest Experiment
"Let There Be Light"

- Equipment
- Data Collection Procedure
- Data Analysis
- Data Table
- Conclusions and Extensions

PASPORT Light Sensor
(PS-2106)

Purpose

To measure the light levels at Selva Verde Lodge over a 24-hour period of time.

Overview

In this activity, students will set an Xplorer GLX and PASPORT Light Sensor outside the Selva Verde Lodge to measure how the amount of light that penetrates through to the Lodge changes over the course of 24 hours.

Background Information

Light is a very important aspect of the rainforest environment.  Within the rainforest, plants exist in a hierarchy, from the tallest tree down to the smallest moss, sharing resources within four basic layers in a tropical rainforest.

Emergents: The few trees that grow above and beyond the canopy layer make up the emergent layer.  They get the full force of drying winds, hot sun, and soaking rain.  In order to better retain water, emergent trees have developed small, leathery leaves.

Canopy: The trees of the canopy are approximately 40 to 70 feet (11 to 20 meters) tall.  The canopy layer, like the emergent layer, also gets the full force of wind, rain, and sun.  This ample supply of sunlight explains why 90% of the rainforest’s photosynthesis occurs in the canopy. 

Understory: Less than 1% of the light that the canopy receives reaches the understory (also known as the subcanopy).  Understory trees have thin trunks, and their crowns are shaped like closed umbrellas.  These trees have also developed larger leaves to better absorb light in the dark forest understory.

Forest Floor: The forest floor is dark, and very little plant life besides ferns and small broad-leafed plants grow here.  Branches, rotten leave and fruit, animal droppings, and other debris that fall from above are quickly removed by fungi, termites, bacteria, and tiny tree roots.  In areas where trees are not as close together and sunlight reaches the forest floor, shrubs grasses, and other forest plants will grow.

Millions of green leaves use each sunlit hour to produce stores of food through photosynthesis.  This occurs at a rapid rate.  Few forests have canopies so dense that no direct sunlight comes through, and the rainforest is no exception.  Each of the small openings in the canopy form small patches of light across the forest floor.  If a species cannot grow in the shade, its seedlings will not survive unless such an opening in the forest canopy is present.  Because storms often create openings big enough to allow full sunlight to reach the forest floor, species requiring significantly high light levels can survive. 

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Equipment:

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Data Collection Procedure

Xplorer Setup:

1. Connect the Light Sensor to the port on the top of the Xplorer GLX.
Note: Be sure that the GLX is fully charged.

2. The Light Sensor has three settings that measure up to a certain capacity of lux. The sensor will continuously monitor incoming light, even when data recording is not taking place, to check whether the amount of incoming light is too high for the given setting. When this happens, the light will flash red. The final setting (sun) will be best for this experiment.

3. Press I to access the Sensors screen. Press c to change the sample rate unit to minutes. Change the sample rate to 5. The sensor is now calibrated to take data once every 5 minutes.

Light GLX Screen

Equipment Setup and Recording Data:

1. Place the Xplorer GLX and Light Sensor outside the Selva Verde Lodge.

2. Turn on the Xplorer GLX and press s to begin recording data. Record the time.

3. Allow the GLX to take data for 24 hours.

4. Collect the setup and press s to stop recording data.

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Data Analysis

1. From the Home screen, press F to access the Graph display.

2. Examine your data.

3. Using the Smart tool (H , 1) to find the approximate sunrise, sunset, and any change in visible weather patterns (rainstorm, clouds, etc.).

Data

  Lux
Start TIme  
End Time  
Recorded Sunrise  
Recorded Sunset  
Actual Sunrise  
Actual Sunset  

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Conclusions and Extensions

1. Did the level of light measured over time correlate to what you expected to see when the sun rose or set?

2. What rainforest characteristics might affect the amount of light reaching the ground?

3. How do rainforest characteristics affect plant growth?

4. Considering the latitude at Selva Verde, would you expect more or less seasonal variation in light intensity here as compare to your hometown?  Explain the difference in terms of the biodiversity in both environments.

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Back to Costa Rica Summary -- October 2002