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This activity demonstrates how light decreases as water depth increases and encourages students to explore the Science Journal app.

Depth and light helps students investigate the relationship between depth and available light before discussing how this might affect deeper corals. This activity will use the Science Journal app. During this activity you will observe the link between depth and light and consider how coral adapts to environments with lower light levels. This activity uses the Science Journal app which has a range of features which make conducting science experiments engaging and exciting. See Subject Update How to: Use the light sensor on the Science Journal app.

What you’ll need

  • A smartphone with the Science Journal app installed
  • Two large spacers (these could be thick books)
  • A large, clear plastic container
  • A ruler or tape measure
  • Water

Live investigations Depth and light image step 2


Activity steps

  • You will be exploring the relationship between depth and available light.
  • Set up your equipment as shown in the diagram.
  • Open Science Journal app on your phone and select light sensor.
  • Press record and slide light sensor under the container of water.
  • Add 2cm of water to the container.
  • Then remove the smart phone and stop recording.
  • Make a note of the minimum exposure value.
  • Predict what the exposure value will be if another 2cm of water is added.
  • Repeat the recording process and make a note of the minimum exposure value each time.
  • Continue until you have added 10cm of water.


  • How was the light sensor affected as more water was added to the container?
  • What does this tell you about light availability in deep water?
  • What does this mean for coral living in deep water?

Safety guidance

  • Caution should be taken to ensure containers are not too full. To avoid spills, keep containers in the middle of the table and clean up spills straightaway to avoid slips. Great care should be taken when positioning smart phones to ensure they are kept dry.

More ideas
Now you have a container full of water, try stirring in a spoonful of soil and taking a light reading. Repeat five times, taking a reading after each spoonful of soil is added. This will make the water cloudy, or turbid. How does the turbidity effect the light sensor? Turbidity can be problematic for coral, why do you think this is? What could cause increased turbidity in oceans?

Find out more
One of the issues scientists face in exploring the deep ocean is its darkness. Water scatters and absorbs light. No light at all penetrates to the ‘midnight zone’, at depths below 1000m. In practical terms, only in the ‘sunlight zone’ at depths above 200m, can scientists see what they are studying without the need for artificial light. Corals have adapted in several ways to live on the deep reef. One of the ways that they have adapted is colour. Corals on the deep reef tend to be darker. Click here to try an experiment designed to test the hypothesis that deep reef corals are darker, because they need to absorb more of the available light.

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