Light and Shadow Experiments for Grades 4–6: A Lesson Sequence

Shadows are one of the few physics topics where every student can run a real experiment with equipment you probably already have. A flashlight, an object and a wall are enough to investigate how light travels, why shadows change size, and why some shadows have soft edges. The topic also gives you a clean way to teach fair testing, because there are only a few variables to control. Below is a lesson sequence for Grades 4 to 6 that follows the structure of our Light, Shadow and Penumbra science unit, which takes four to six lessons.

What you need to prepare

For each group, an LED flashlight, an opaque object (a small toy or a block works), a screen or a stretch of plain wall and a ruler. For the lesson on two light sources, each group needs a second flashlight. Dim the room if you can; shadows are easier to measure with less background light.

Set up the safety rule before anyone switches on a lamp: do not stare into bright light, and never look at the Sun. Repeat it before the outdoor lesson, since students tend to look up when they are thinking about the Sun.

A tip from experience: mark the object and screen positions with tape on the table. It keeps the fixed distance fixed, which matters for the second lesson.

A lesson sequence that builds the model

Each lesson follows four phases: a 10-minute Engage, 20 to 30 minutes of Explore, 30 to 45 minutes of practice and a 15 to 20 minute Reflect. The content moves from observation to explanation:

• Observe a shadow: light travels in straight lines, and an opaque object blocks it.
• Change distances: keep the object-to-screen distance fixed, change only the lamp distance, and measure the shadow.
• Sketch light paths: draw boundary rays from the lamp past the edges of the object.
• Two light sources: find full shadow, partial shadow and fully lit regions.
• Experiment error: spot the flaw in a test where two things changed at once.
• Shadows outside: explain long and short shadows through the height of the Sun.

The measuring lesson is the heart of it. Students usually predict that moving the lamp closer makes the shadow smaller, and are surprised when it grows. That surprise is exactly what you want before the ray-sketching lesson, because the drawing explains what they just measured.

Teaching umbra and penumbra with two lamps

Full shadow and partial shadow are easiest to understand with two flashlights. Have students shine both at the object and look at the screen. Some areas are dark, some are gray, some are bright. Then ask them to count: how many lamps reach this spot? Zero lamps means full shadow, the umbra. One lamp means partial shadow, the penumbra. Both lamps means fully lit. Counting turns a fuzzy idea into something students can check with their hands, by blocking one lamp at a time.

The technical words are optional at the lower end of the range. Fourth graders can work entirely with "full shadow" and "partial shadow" and meet umbra and penumbra later.

Differentiating the investigation

All six worksheets have foundation, core and extension versions. Foundation students might record shadow sizes in a prepared table and circle whether the shadow got bigger or smaller. Core students write a conclusion sentence that names the one thing they changed. Extension students predict the shadow size for a lamp distance they have not tested and then check it.

Students who need more help with measuring and recording data will benefit from extra practice in that area. The Measurement, Data Analysis and Scientific Inquiry unit for Grades 5–7 works on those skills directly. If your art teacher is looking for a cross-curricular link, the light, shadow and shading drawing unit takes the same ideas into observational drawing for older students.

Checking understanding

Two questions tell you most of what you need to know. First, "What did you change, and what did you keep the same?" A student who can answer that clearly understands the fair test. Second, "Why is there a gray area around the dark shadow?" A student who says "because only one lamp reaches it" has the model.

The experiment-error worksheet is also a strong assessment in itself. Students who can spot that two variables changed and explain why that makes the result useless have learned something that transfers to every future science investigation. The learning check and the model answers in the teacher guide round out your evidence.

For an overview of the topic and its goals, see our page on teaching light and shadow science in Grades 4–6.

Related reading from the Teacher Hub

• Teaching Fair Tests with Shadows: Umbra, Penumbra and Common Errors
• How to Teach Sample Space and Events with Dice in Grades 5–7
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