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The Colors of Solar Energy

Through experimentation with bottles of different colours, you will know which colours absorb more sunlight (infrared rays) and which colours may be more beneficial to harness the sun's heat energy.


Develop these Key Competencies

  • Critical thinking

Materials needed

  • Four PET bottles (plastic bottles) painted with different colours or covered with coloured paper
  • Water
  • Thermometer
  • Table for recording temperature measurements
  • Pen
  • Paper
Activity Development

In this fascinating experiment aimed at young people aged 7 to 10, we will explore how different colours absorb heat from sunlight. Using simple materials like PET bottles and water, we will compare the temperatures of bottles painted with different colours after exposure to direct sunlight. Let's uncover the mysteries of infrared rays and discover which colours can keep things cooler or warmer!

 Safety Note

 As at least the beginning and the end of this experiment have to be done in direct sunlight, it is very important to take the corresponding protection measures. Use sun screen, wear a hat, maybe wear clothes with long sleeves and long legs, make sure to drink enough water and go to the shade from time to time during the outdoor experiments. 

Activty Description

Step 1: Prepare the Bottles

  • Paint each PET bottle with a different color or cover them with paper of different colors to make them stand out from each other.Make sure that one is black and one is white.
  • Fill all four bottles with equal amounts of water from the tap, almost filling them to the top.

Step 2: Record Initial Temperatures

  • Measure and note the initial temperature of the water in each bottle. Use a thermometer to do this and record your findings in a table.

Step 3: Predict and Place in Sunlight

  • Take a moment to guess which bottle you think will get the hottest when placed in direct sunlight. Write down your estimate.
  • Place all the bottles close to each other in direct sunlight, ensuring they receive the same amount of sunlight exposure.

Step 4: Measure After 20 Minutes

  • Wait for about 20 minutes to allow the bottles to absorb heat from the sunlight.
  • After the time has passed, measure the water temperature in each bottle again.

Step 5: Analyze the Results

  • Compare the ranking you predicted with the actual measurements you took. Fill in the comparative table with your findings.
  • Which bottles contain the hottest water? Why do you think this happens?

Step 6: Post-Activity Actions

  • Once you have finished the experiment, move the bottles to a shaded area and allow them to cool down.
  • After they have cooled, make good use of the water by, for example, watering the plants in your home or garden.
  • Re-use the bottles to do the experiment with another group or recycle PET bottles (if they are painted, they would need to be put to the garbage), to be environmentally friendly!


Exploring the Science Behind Colors and Light Absorption

  • Dark colours absorb more heat from sunlight because they absorb more light energy, particularly infrared rays. Colours closer to black absorb the most heat from the radiation source.
  • Colors that reflect more light waves tend to be cooler, while those that absorb more light energy become warmer.


Reflection Questions

  • Which colours absorb more energy from sunlight and transform sunlight into heat more effectively?
  • Think about situations in your daily life where you have seen and experienced this effect, regarding colors and heating by the sunlight (for example dark clothes in summer)
  • Knowing this effect, what can you do in your everyday life to take advantage from this effect ('to absorb the heat to warm something up or to reflect the heat to keep it cool)?
  • What other actions can you take to raise awareness for a more sustainable way of using energy and leading by example?


Relevant information if you are facilitating

Activity Goal

This activity aims to provide young participants (aged 7 to 10) with an interactive and insightful experience that highlights how actions in the home can influence the community and the environment. Through a fun experiment involving PET bottles with different colours, participants can estimate water temperatures and observe the impact of ecological practices. By incorporating creative elements like drawing faces on the bottles, we aim to foster curiosity and enthusiasm while encouraging sustainable habits and environmental awareness within their homes, families, and friend circles.


Activity Overview


  1. Introduce how individual actions at home can contribute to the community's and the environment's overall well-being.
  2. Initiate a conversation about ecological practices and their positive impact on sustainability. Emphasize the significance of small changes at home leading to broader community and environmental benefits.
  3. Encourage participants to share their learnings and inspire others within their homes, families, and friend circles to adopt eco-friendly habits


Key Takeaways for Participants

  • Understanding how individual actions at home can have a collective impact on the community and environment.
  • Exploring the science of colors and heat absorption, and how dark colors tend to absorb more heat due to their ability to capture more light energy, including infrared rays.
  • Realizing that small ecological practices, such as conserving water, recycling, reducing plastic use, and saving energy, can make a positive difference in creating a sustainable future.
  • Emphasizing the importance of spreading environmental awareness within their immediate circles to inspire a broader positive change.


Safety Considerations

  • Prioritize sun safety during outdoor activities. Participants should use sunscreen, wear protective clothing, and stay well-hydrated.
  • Ensure that all materials used in the experiment are safe and age-appropriate.



By combining scientific exploration, creative expression, and environmental consciousness, this activity aims to empower young minds to become eco-champions in their homes and communities. Through their active participation and newfound awareness, they will be better equipped to take meaningful steps towards a greener, more sustainable future. Let's ignite their passion for positive change and watch as they become catalysts for environmental preservation and awareness.


Time needed

50 minutes


  • While the painting or glue is drying and while the experiment is running, there is time to do other things.The experiment can be started, then other activities can be done, and after about 30 minutes, the follow-up of the experiment can be done.

Age range

  • 7 to 10

Useful links


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Time needed

50 minutes


  • While the painting or glue is drying and while the experiment is running, there is time to do other things.The experiment can be started, then other activities can be done, and after about 30 minutes, the follow-up of the experiment can be done.

Age range

  • 7 to 10

Useful links