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Activities / Creative Corner / Holidays

The Science of Light Sticks – Liquid Light

Just give the plastic light stick a little “snap” and a shake and the liquid inside begins to glow. Some people call it liquid light. Light sticks are more popular than ever and have become almost required apparel for Halloween to cast an eerie glow on the candy seekers. I always buy them for my girls to wear while trick or treating. Did you know you can learn a little science from light sticks? Light sticks are also a great and inexpensive teaching tool to learn how temperature affects the rate of the chemical reaction.

**Caution! This experiment requires the use of very warm water, which requires the assistance of an adult helper.

Take advantage of the holiday and stock up on some light sticks during the Halloween close-outs. You’ll need three light sticks of the same size and color for this experiment. You’ll also need two glass containers (coffee cups or beakers work well) and a darkened room.

In the following experiment, you’ll observe the differences in the brightness of the light given off from a light stick placed in hot water and and an identical light stick placed in cold water.

mhm-liquidlight2In a darkened room, remove one light stick from its package and feel the outside of the light stick to determine its approximate temperature. Bend the light stick until you hear it “snap” and the liquid begins to glow. Shake the light stick to mix the liquid inside. Feel the outside of the light stick again. Has the temperature changed?

Have an adult fill one of the glass containers with cold water (a mixture of water and ice) and the other with hot water. Ideally you would like to have the hot water around 50 degrees C / 120 degrees F. Be careful not to make the water too hot (above 70 degrees C / 158 degrees F) because it can melt the plastic of the light stick. Never place a light stick in water that is being heated.

At the same time place one light stick in the hot water and place one light stick in the ice water. Leave the third light stick at room temperature. How long does it takes for a change to occur in the hot-water light stick and in the ice-water light stick? What happens to the light intensity or brightness of each light stick? Look closely at the hot-water light stick without removing it from its container. Notice the bubbles rising to the top of the light stick. Compare the rate of bubble formation between the three light sticks. If you have difficulty seeing the bubbles forming, you may have to remove the light sticks from their containers and hold them up to a light source such as a window. What causes the bubbles to form?

After a few minutes, reverse the light sticks so that the warm light stick will be placed into the cold water, and the cold light stick into the warm water. How long does it takes for the intensity to change (how long will it take the dim light stick to brighten, and the bright one to dim)?

Remove the light sticks from the hot water and the ice water. Allow them to come to room temperature. What happens? How long do you observe any changes?

For more on the science of liquid light click here.

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Guest blogger Susan Wells is the mom to two girls, ages 4 and 8. She enjoys enriching her daughter’s education by finding the learning in everything. They especially enjoy science activities. She works as a blogger and social media strategist for Steve Spangler Science, a Colorado company dedicated to helping teachers and parents get children excited about science.

Susan Wells
Author: Susan Wells

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