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Light Instruments: Discovering Shadows

Design and build a musical instrument that responds to changing light.

At least 10 minutes each to set up, discover the range of light levels, explore shadows, and investigate transparency.

Tools and Materials

  • Download the Science Journal app
  • Flashlight
  • Paper, plain white 8.5” x 11” or larger
  • Papers of as many assorted colors as possible, cut into squares roughly 3”x 3”
  • Pencil
  • Various materials and objects of differing transparency, such as fabrics, plastics, tapes, etc.

Body Conductivity
Tip

When facilitating this activity with a group, create an audible or visual signal (such as a clap or a hand gesture) to indicate when learners should switch their phone audio on or off. This will help control noise levels in the room.

Noise levels will also be reduced if you limit the number of phones that are on during the Reading the Room for Light and Darkness phase. For larger groups, have learners pair up and take turns holding the phone.

Facilitator Note

This guide was written to support facilitators leading others through the activities. Whether you are a facilitator, student, interested individual, or all of the above, we hope you use these materials in any way that is useful to you. Follow step-by-step instructions or make the activity your own. We wrote this activity with some assumptions in mind. Your situation may be slightly different, so these should guide you in how you may need to adapt.

Assumptions:

Learners are at least 10 years of age.

You’ll need 5–10 minutes prior to doing the activity to download the app on one phone.

Both facilitator and learners are familiar with Science Journal and its Project, Experiment, Trial setup by going through the Getting Started activities.

The facilitator has run through the activities prior to facilitating. If this is not possible, we hope that a facilitator will do the activity alongside their learners to better understand what is going on.

The activity is designed to boost inquiry-based learning skills and scientific practices, not meet specific goals regarding the content.

Here you’ll explore how light sensors behave under different lighting conditions, how light affects shadow, and how materials have different transparency. You will also experiment with the audio feature in Science Journal that translates data points into sound.

Setup

1. Open Science Journal. Start a new experiment, then select the sensor icon in the bottom tool drawer

2. Select the Ambient Light sensor.

Body Conductivity Note: Some phones do not have an Ambient Light sensor. If you don’t see the lightbulb appear in the app toolbar, don’t worry. You can use an external light sensor for all of these activities. For more information on how to connect your external light sensor to your phone, see setting up the photoresistor.

3. Locate the light sensor.

If you don’t know where to find it on your phone, try the Getting Started with Light activity.

4. Enable audio by selecting the three vertical dots on the far right side of the screen and tapping Enable audio.

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The audio feature in Science Journal translates sensor data into sound. As the data value increases, the pitch goes up. As the data value goes down, the pitch goes down.

Tip

There are multiple sonification options in the app. We recommend using the Default setting to start, as it gives the largest tonal range. When you are ready to transition into building light instruments, we recommend using the Scale option as it is more melodic.

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Reading the Room for Light and Darkness

Discover the range of light levels that we experience in our daily life.

1. Hold the phone in the palm of your hand so the screen is facing up toward the ceiling or sky.

Watch the meter as you listen to the sound. What measurement do you get?

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Note: The Ambient Light sensor measures illumination in units of lux. To learn more about this unit of measurement, click on Learn More in the app.

Tip

For ease of comparison between different phones, we suggest having learners observe in meter mode rather than graph mode. You can toggle between these views by selecting either Graph mode to see the graph or Meter mode to see the meter.

2. Take 10 steps in any direction.

Notice what happens to the light levels.

Questions you may ask:

  • Did your eyes detect a change in light?
  • Did the sensor detect a bigger change in light than your eyes did?
  • How does tilting the phone in different directions change the data value?
  • Can you find a way to keep the reading steady?
  • What other challenges can you come up with?

3. Look around.

Take some time to observe your environment and determine which factors might be affecting the reading.

Questions you may ask:

  • Is your own shadow having an impact on your reading?
  • Where in the room do you get the highest note/greatest value?
  • Where do you get the lowest note/lowest value?
  • What happens if you find a different type of light (a window, a flashlight, an LED bulb, or an incandescent bulb)

Casting Shadows

Explore how complex shadows can be.

1. Place a sheet of plain white paper on a table or desk.

2. Hold your hand above the sheet of paper.

Start far away from the paper and then bring your hand closer to the paper’s surface.

Tip

If you’re having trouble casting a solid shadow, try finding a brighter light to work under or hold a flashlight above your hand. If you have access to multiple types of light sources, try several and compare.

Questions you may ask:

  • How does your shadow change when you move your hand?
  • What light conditions give you the sharpest shadow?
  • Can you find a way to make multiple shadows?
  • Does your shadow look different when it’s made by natural light versus an incandescent bulb? A compact fluorescent (CFL)? An LED?
  • Try casting shadows with other objects. What do you notice?

3. Hold your hand in one spot above your paper and try tracing your hand’s shadow.

It might be easier to do this with a partner. You can also try tracing an object that doesn’t move, such as a water bottle.

Questions you may ask:

  • What did you notice about portions of your shadow that are easier or harder to trace? When you finish tracing, does your drawing look like a hand or something else?
  • What ideas do you have about what happened?

4. Place the phone’s Ambient Light sensor with audio enabled in different parts of your cast shadow.

Questions you may ask:

  • Where do you think you’ll find the highest value? The lowest? Are the readings what you expect?
  • Can you close your eyes and tell by the audio when the sensor is in the shadow and when it is not?

Investigating Transparency

Find out how much or how little light can travel through different materials.

1. Gather your materials and enable audio.

Have your paper squares and various transparent, translucent, or opaque materials on hand, and enable the audio.

2. Place one paper square on top of the light sensor.

Give yourself enough room to still read the screen. Are your readings the same as those of others around you?

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3. Now try this again with each of the paper squares.

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Questions you may ask:

  • What were the highest and lowest values after placing the paper squares in order of lowest to highest lux value?
  • Did anything surprise you?
  • What ideas do you have about what happened?

4. Now try nonpaper materials.

Try fabric, your finger, a coin, or a piece of plastic.

Questions you may ask:

  • Can you order them from lowest to highest lux level? Are you surprised?
  • What ideas do you have about what happened?
  • Can you find two different materials that give the same lux reading?

5. Try shining a flashlight through various materials.

Hold each material up to a light source and look through it. If you don’t have a flashlight you can use the flashlight on your phone, a lamp, or even a bright window.

Questions you may ask:

  • According to your eye, which item lets through the most light?
  • Is this “eye reading” in keeping with your sensor readings?

What's Going On?

Your phone detects light thanks to a semiconductor device called a photoresistor. A photoresistor is a light-sensitive electrical current regulator; you can think of it as a valve for electricity. When lots of light hits the surface of the photoresistor, the valve opens and electricity can flow freely through the circuit. When there is less light, the valve shuts and the photoresistor lets less electricity through.

Different materials placed in front of the phone’s photoresistor let different amounts of light through. Light encountering a solid material can be reflected, absorbed, or transmitted—or a combination of the three. Transparent objects transmit light, opaque objects absorb light, and translucent objects transmit some light while absorbing the rest.

The various papers and materials you experiment with here will have varying opacities, depending on their thickness, density, and the dyes they may contain.

Strictly speaking, the light sensor in your phone does not detect color. However, you’ll probably find that different colors of paper transmit differing amounts of light, thanks to their different degrees of light absorption.

An opaque object casts a shadow—a region where light can’t reach. The character of this shadow depends on the light source that creates it. Large, distant light sources or nearby pinpoint light sources produce sharp shadows. In contrast, large, nearby light sources produce blurry shadows.

Areas of total shadow—called umbra—are rare. More often, what you see are penumbra, partial shadows where some light is blocked but other light fills in.

Clouds have varying levels of transparency. They cast mottled shadows on the landscape without creating complete darkness.

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Sunglasses block our eyes from some sunlight but still let enough through so we can see the world around us.

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Curtains help to keep out light. The thicker the fabric, the less light gets through.

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A sharp shadow is produced when something opaque blocks a distant light source such as the Sun.

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Soft shadows are produced by translucent objects and diffuse light sources.

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Want to learn more about light and shadow?

Exploratorium artist and exhibit developer, Bob Miller, explored light and shadow in his 1982 video Light Walk. You can watch a clip and try some activities. Discover how light reflects and refracts through different materials in an activity developed at the Exploratorium’s Teacher Institute. Are you curious as to why different light sources result in different sensor readings? Watch CD Spectroscope and learn about the different wavelengths that make up light, then build your own spectroscope to discover these different wavelengths yourself.