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Experiment with light

Experiment with light
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Build a simple spectroscope from a cardboard tube, CD, and flashlight to split light into colors and explore reflection and refraction.

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Step-by-step guide to build a simple spectroscope

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Light Experiment | Kids Science

What you need
Adult supervision required, black paper, cardboard tube, cd or dvd, flashlight, pencil, ruler, scissors, tape

Step 1

Gather all the materials listed and bring them to a clean table.

Step 2

Ask an adult to help you before you use scissors or make any cuts.

Step 3

Use the ruler and pencil to mark and trim the cardboard tube to about 20 cm long.

Step 4

Cut two small rectangles of black paper about 4 cm by 2 cm.

Step 5

Tape the two black paper rectangles over one end of the tube leaving a narrow gap of about 2 mm between them to form a slit.

Step 6

Use scissors to cut a diagonal slot about 2 cm long near the opposite end of the tube at a 45° angle.

Step 7

Slide the CD into the diagonal slot with the shiny side facing the slit and the edge of the CD tilted toward the middle of the tube.

Step 8

Tape around the CD gently so it stays at that angle and does not wobble.

Step 9

Cut a small round viewing hole about 1.5 cm wide next to the CD on the end of the tube so you can put your eye close to the CD.

Step 10

Turn off the room lights so the room is dim.

Step 11

Have an adult hold the flashlight about 20 cm away and point the beam straight at the slit.

Step 12

Look through the viewing hole and slowly tilt the tube or CD until you see a rainbow of colors appear inside the tube.

Step 13

Take a picture or make a drawing of the colors you see and share your finished spectroscope and your discoveries on DIY.org

Final steps

You're almost there! Complete all the steps, bring your creation to life, post it, and conquer the challenge!

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Help!?

What can I use if I don't have some of the listed materials like a CD or black paper?

If you don't have a CD use an old DVD or a small piece of shiny gift-wrap cut into a disc and slid into the diagonal slot (step 6), and if you lack black paper cover the slit with black electrical tape or paint it black (step 5).

I don't see any rainbow—what likely went wrong and how can I fix it?

If no colors appear, make sure the slit is about 2 mm wide (step 5), the CD is tilted and taped securely in the 45° diagonal slot (steps 6–7), the flashlight is about 20 cm away and aimed straight at the slit (step 11), and the room is dark (step 10), adjusting each until a spectrum shows inside the tube (step 12).

How can I adapt this activity for different ages?

For younger kids have an adult do the ruler measurements, cutting of the tube and the diagonal slot (steps 2–6) while the child tapes the CD and decorates the tube, and for older kids add a protractor to fine-tune the CD angle, record different tilt settings, and photograph spectra through the viewing hole (steps 6–9, 12).

How can we extend or personalize the finished spectroscope?

To extend the activity compare spectra from different light sources (flashlight, sunlight, lamp), try a diffraction grating instead of the CD in the diagonal slot for sharper lines (step 6), secure the flashlight at a fixed distance with a clamp for repeatable tests, and decorate before sharing your results on DIY.org (step 12).

Watch videos on how to build a simple spectroscope

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Refraction Of Light In Water | Science Experiments for Kids | Sema's Lab

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Facts about light and optics

💿 A shiny CD's tiny grooves act like a diffraction grating and can separate light into rainbow patterns.

🔬 A spectroscope splits white light into its colors so you can see the different wavelengths — red is about 700 nm and violet about 400 nm.

🔦 Even a plain white flashlight is made of many colors; your homemade spectroscope will reveal them.

👀 Human eyes can distinguish roughly one million different colors, but a spectroscope shows the exact wavelengths that make them up.

🌈 Isaac Newton used a prism in the 1660s to prove white light is made of all colors, kickstarting the study of light.

How do I build a simple spectroscope from a cardboard tube, CD, and flashlight?

To build a simple spectroscope, cover one end of the cardboard tube with black paper and cut a narrow vertical slit at the other end. Angle a small piece of CD inside the tube so its shiny side faces the slit; tape it in place at about 30–45°. Point the slit toward a light source and look through the tube’s open end; the CD will diffract light into a rainbow. Adjust the CD angle and slit width to sharpen the spectrum. Never point it at the sun or bright lasers.

What materials do I need to make a cardboard tube spectroscope?

You’ll need a cardboard tube (paper towel or wrapping paper roll), a CD or DVD (the shiny side), a small flashlight or LED torch, black construction paper or tape to block stray light, scissors or a craft knife, ruler, pencil, and tape or hot glue. Optional items: extra CDs to compare diffraction, colored filters, and a protractor to measure angles. Supervise kids when using sharp tools and cutting the CD.

What ages is building a simple spectroscope suitable for?

This spectroscope project suits children around 6–12 with adult help; younger kids (4–6) can join with close supervision for cutting and handling the CD. Older children (12+) can work more independently and expand experiments by measuring angles and comparing light sources. The craft needs some fine motor skills for cutting and taping, so match tasks to your child’s ability and always supervise when using sharp tools or bright lights.

What safety precautions should I follow when doing this light-splitting experiment?

When doing this experiment, never look directly at the sun or bright lasers through the spectroscope; use artificial lights or indirect sunlight. Supervise all cutting and handling of the CD—edges can be sharp—and cover sharp points with tape. Use child-safe scissors, keep small parts away from very young children, and avoid hot glue near fingers. If testing lamps, let bulbs and batteries cool to prevent burns and review eye safety before starting.
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