Light, colour and rainbows are fascinating, and you can explore all of them with simple bits and pieces at home. The experiments outlined below focus on being easy to follow, fun and practical for families, clubs or classrooms. 

Light, colour & rainbows

Light is a form of energy that travels in waves, and the tiny part we can see is called the visible spectrum (roughly 400–700 nanometres). When light meets materials like water, glass or plastic, it can bend (refraction), bounce (reflection), spread into colours (dispersion) or be absorbed, which is how we get effects like rainbows. 

Experiment 1: Homemade rainbow

This simple setup copies how real rainbows form in raindrops using just a glass of water and sunlight.^[1]

You’ll need:

·       A clear glass filled with water

·       A sheet of white paper

·       A sunny window or a bright flashlight

What to do:

1.      Put the glass of water on a table near a sunny window.

2.     Place the white paper on the floor or wall opposite the light source.

3.     Gently move the glass until the light passes through the water and a rainbow appears on the paper.

What’s going on:
White light bends as it enters the water, and each colour bends by a slightly different amount.
Red bends the least and violet the most, so the colours spread out into a rainbow, just like they do in raindrops in the sky.

Experiment 2: Spinning colour wheel

This activity shows how colours of light can blend together when they move fast.

You’ll need:

·       Cardboard or thick paper

·       Red, green and blue markers (RGB)

·       A pencil or dowel for spinning

·       Scissors

What to do:

1.      Cut a circle from the cardboard.

2.     Divide the circle into equal wedges.

3.     Colour the wedges using red, green and blue in a repeating pattern.

4.     Poke a hole in the centre and push the pencil or dowel through.

5.     Spin the wheel quickly and watch the colours.

What’s going on:
When the wheel spins fast, your eyes can’t separate the colours and they blend into a whitish or grey colour.
This is additive colour mixing, the same idea used in screens where tiny red, green and blue lights mix to make all the colours you see.

Experiment 3: Prism rainbow (or CD spectrum)

This classic experiment splits white light into a full spectrum of colours.

You’ll need:

·       A glass prism (or a CD/DVD as a substitute)

·       A flashlight or sunlight

·       A darkened room

·       A white wall or sheet of paper

What to do:

1.      Darken the room slightly so the beam of light is easy to see.

2.     Shine the flashlight through the prism.

3.     Tilt and turn the prism until a band of colours appears on the wall or paper.

4.     If using a CD/DVD, shine the light onto the shiny side and look at the reflected colours.

What’s going on:
The prism bends each wavelength of light by a different amount, so shorter wavelengths (blue and violet) bend more than longer ones (red).^[1]
This spreading is called dispersion and reveals that white light is made of a continuous range of colours. 

Experiment 4: Cereal-box spectroscope

Turn a cereal box and an old CD into a simple tool for looking at the “fingerprints” of different light sources.

You’ll need:

·       An empty cereal box

·       An old CD or DVD

·       Aluminium foil

·       Tape and scissors

·       Different light sources (bulb, LED, candle, etc.)

What to do:

1.      Cut a narrow slit at one end of the cereal box for the light to enter.

2.     At the other end, cut a small viewing hole.

3.     Inside the box, tape a piece of CD at about a 45° angle with the shiny side facing the slit.

4.     Cover any other openings with foil so stray light is blocked.

5.     Point the slit at a light source and look through the viewing hole to see the spectrum.

What’s going on:
The CD acts like a diffraction grating, splitting the light into a pattern of coloured lines or bands.
Incandescent bulbs give a continuous rainbow, while many LEDs show distinct lines or gaps, hinting at how different atoms give off specific colours of light. 

Experiment 5: Colourful shadows

This one turns shadows into bright, surprising colours using three coloured lights.

You’ll need:

·       Three torches (flashlights) with red, green and blue filters (coloured cellophane works well)

·       A white wall or large sheet of white paper

·       An object to cast shadows (a toy, your hand, etc.)

·       A dark room

What to do:

1.      In a dark room, aim the three coloured torches at the wall from slightly different angles.

2.     Place the object in front of the wall so it blocks some of the light and creates overlapping shadows.

3.     Move the object a little and watch how the shadows change colour where different lights are blocked.

What’s going on:
Where one coloured light is blocked, the other two mix to make a shadow in the complementary colour (for example, blocking red leaves green and blue, which make cyan).
This shows subtractive colour mixing and how our eyes and brain combine overlapping wavelengths to create the colours we think we see. 

Going further with Curious Minds kits

These simple experiments use everyday materials and link neatly to topics like light, colour and vision in the UK science curriculum (for example, Key Stage 2). They can also be adapted for science clubs, team-building sessions or remote learning.

If you’d like ready-made resources to take these ideas further, you can try:

·       Holographic Diffraction Grating Film (unmounted) 1000 lines per mm – Great for creating sharp rainbow patterns and exploring diffraction.

·       Build a Working Solar Projector Science Kit for Age 12 & Up – Build your own projector to safely study sunlight and optics.

·       Newton’s Prisms – a high quality optical glass prism which can be hung from windows to watch the sunlight being split into its individual colours.