Light Sticks

There are many different sources of light, including a variety of chemical reactions that produce light. Combustion reactions produce light and heat, but some chemical reactions give off light without heat. Chemiluminescence is the light produced by these nonthermal chemical reactions. This experiment introduces chemiluminescence and investigates the effect temperature changes have on the intensity of the light.

 

Materials

3 light sticks of the same color

Container of hot water (no warmer than 70 oC)

Container of cold water

 

What To Do

Activate one light stick by bending the plastic enough to break the glass vial inside. Pass it around so everyone can feel that heat is not being produced with the light. Activate the other two light sticks. Place one in the container of cold water and the other in the container of hot water. Keep the first light stick at room temperature as a control. After a few minutes remove the light sticks from the water and compare the intensities with that of the control. Place the light stick that was in hot water in cold water and place the one that was in cold water in hot water. After a few minutes remove the light sticks from the water and compare the intensities.

 

Questions

1. Once activated, do light sticks increase, decrease, or remain the same temperature?

2. Did increasing the temperature of the light stick increase or decrease the intensity of light? Why?

3. When the temperatures of the light sticks were reversed did the intensities reverse? If so, how long did it take?

 

Summary

  Some chemical reactions produce light without producing heat. The light produced by these reactions is called chemiluminescence. The light sticks consist of two solutions enclosed in a plastic tube. Phenyl oxalate ester and a fluorescent dye make up one solution. The other solution, dilute hydrogen peroxide, is sealed in a glass vial inside the plastic tube. When the light stick is bent to activate it the vial of hydrogen peroxide is broken so the two solutions can react. The chemical reaction gives off energy as light, or chemiluminescence. Since the light is produced by a chemical reaction and most chemical reaction rates are affected by temperature, a change in light intensity with a change in temperature is expected. Generally the rate of a reaction increases with increasing temperature. For this reaction, an increase in the reaction rate results in an increase in light intensity. This is easy to see when the light sticks are placed in hot and cold water. Extension Chemiluminescence in living creatures is called bioluminescence. Coleptera Lampyridae beetles, better known as fireflies or lightning bugs, use a chemical reaction within their bodies to produce light. Model lightning bugs can be made in the classroom using light sticks and a few craft supplies.

 

Sources

"Teaching Physical Science through Children’s Literature Fireflies!" Julie Brinckloe. ISBN 0-689-71055-0

© S. Olesik, WOW Project, Ohio State University, 2002.