Make a Simple DIY Spectroscope

Homemade spectroscope.

Ever looked at a rainbow and wondered how all those amazing colours seem to just burst out of nowhere? This activity will help you create your own rainbow by dispersing a source of light to form a visible spectrum of colours with a simple spectroscope.

Constructing a simple spectroscope is a fun way to begin exploring the physics of light. It’s a simple STEM craft activity ideal for both home and classrooms. It could even make a fun science fair project.

The difficulty level is easy and took us around 30 minutes (plus decoration time) – though this will depend on ability level and the amount of detail with which you choose to customise your spectroscope.

Learning Opportunities

Although our basic homemade DIY spectroscope may not match the complexity of instruments used by scientists,  it gives us a glimpse into some of the scientific principles they use to explore and understand our universe. Hopefully, building this spectroscope will inspire you to learn more about the electromagnetic spectrum, visible light, and the different ways scientists use spectroscopy to further our understanding of the world.

  • Learn about light and the electromagnetic spectrum.
  • Explore diffraction and dispersion of light.
  • Discuss real-world applications in astronomy and chemistry.
  • Observation and analytical skills in comparing different light sources.

Constructing the Spectroscope

What you’ll need

Materials needed for building a homemade spectroscope.

  • Rectangular packaging
  • Black card
  • Black electrical tape
  • Craft knife/scissors
  • Ruler
  • Protractor
  • Pen/pencil
  • A blank compact disc
  • Paints for decoration (optional)

We only need a few basic materials and tools to build our spectroscope. We’ve used a craft knife here, which should only be used under strict adult supervision. Ensure that safety precautions are always observed, especially when handling sharp tools. It’s recommended that an adult perform the cutting tasks of the activity. Before you begin, also ensure you have a clean, stable surface to work on.

How to Make Your Spectroscope

Step 1

Marking out a reference line.

Using a ruler and pencil, mark out a line all around the base of the packaging about 1.5cm up.

Step 2

Use a protractor to mark 45 degree angles.

Using your line as a guide, and using a protractor, mark a 45-degree angle on one side of the packaging.

Repeat this on the other side and then join the two 45 degree lines with a horizontal line along the back of the packaging.

Step 3

Cutting a slit for the CD.

Very carefully, cut along your 45-degree lines and the line at the back. Don’t cut all the way down – leave a small gap, as in the photo.

Slot your CD into the slit you’ve just made. It should fit evenly in the middle and be shiny side up.

Step 4

Cutting a viewing hole.

Very carefully cut a slot to act as the viewing hole. This doesn’t need to be too big as we want to avoid outside light from getting into this hole. If using a craft knife, ensure appropriate safety precautions are taken, and a responsible adult is on hand to help.

We are aiming to avoid excess light leaking into our box. Use black electrical tape to seal the gaps between the packaging and the compact disc. Sticky electrical tape is ideal for this task as it blocks out light and usually has a good degree of stretch to it.

Step 5

Making the slit for a light source.

Cut any flaps off the top of the packaging, leaving a completely open top. Now measure the dimensions of the top of the box and cut the same-sized shape out of some black card.

Next, cut a slit into the square shape. This slot will be where the light source enters the spectroscope. It should be quite narrow (1-2mm if possible). If this slit is cut too large, it can affect the clarity of the spectrum.

Finally, attach the card to the top of the spectroscope using electrical tape. Align the slit horizontally with the viewing hole. This step can be tricky, so take your time and ensure that it’s fully stuck down and there are no gaps around the edges.

You may find it easier to cut the square slightly wider than it needs to be and fold the edges so that it sits in place before sticking.

Step 6

Using the spectroscope.

Now, you’re ready to look through the viewing window and see the spectrum. Try viewing a variety of light sources, such as LED lamps, phone screen lights and daylight.

It’s important to note that you should never point your spectroscope directly at the sun!

How Does a DIY Spectroscope Work?

Light is composed of different colours, like a rainbow. We can use a spectroscope to make these colours visible to us by separating light into its individual parts. When light passes through the slit at the top, it bounces off the CD. This acts as a filter known as a diffraction grating, which spreads the light. This allows us to see the colours within the visible light part of the electromagnetic spectrum.

Customising Your Spectroscope

Experiment with different refractive materials. Is there a difference between various CDs and DVDs, for example? You might also want to try adjusting the width of the slit at the light’s point of entry to see how this affects the detail of what you’re able to see.

Visually, feel free to decorate the outside of your device to make it look interesting. We decided to go with a simple rainbow theme for obvious reasons!

Exploring Different Light Sources with Your Homemade Spectroscope

Using your spectroscope to examine various light sources can be an enlightening experience (pun intended). Each type of light you observe will have its own unique spectrum characteristics.

Comparing different light sources with the spectroscope.

Daylight. This should produce a continuous spectrum consisting of all the different colours in the rainbow.

LED lamp. How does this look different from daylight? Are certain colours more prominent? Are any missing? 

Phone screen. This might look very different from the other two. That’s because many screens use a combination of red, green and blue to make the colours (RGB).

Try drawing what you see or taking a photo through the viewing hole to record the results and then describe what you see.

Opportunities for Additional Learning (Extension Tasks)

Constructing a basic spectroscope can provide a nice entry point for related learning activities. In addition to exploring different light sources as mentioned above, here are a few additional ideas for extension tasks if you’re in a classroom setting.

Exploring Historical Context

Assign a task in which students can research the historical significance of spectroscopy in scientific discovery. Learners can explore how it has been used to further our understanding in astronomy, environmental science and even art and design.

DIY vs Commercially Available

If you have access to a commercially available spectroscope, explore how it differs to the basic homemade version. Explore the differences in performance and potential applications. What can you do with it that you can’t achieve with a basic homemade one?

Spectrum-themed Art Project

Combine science with art by getting students to interpret their findings as colourful artistic representations. This activity could also integrate with exploration of the colour wheel and mixing colours/paints together.

Further Learning

For those eager to learn more about light and colour, understanding how spectroscopy is used in scientific research can be fascinating. It’s an important tool in astronomy for example, where scientists can use it to decipher the composition of different celestial bodies. Whilst this kind of science obviously extends far beyond our simple homemade spectroscope, perhaps it has given some food for thought and sparked an interest in the fascinating world of light and colour?

Check out these great resources which give a more comprehensive introduction:

Looking for more fun STEM-based activities to try? Why not have a go at building and racing a balloon-powered car?