Light Refraction Experiments: Prisms, Rainbows and RGB Colour

Why Does Light Change Direction and Colour?

Light may appear to travel in a simple straight line, but its behaviour changes when it passes from one material into another. A beam entering glass, water or another transparent material can change direction, reflect from a surface or continue through it. Under the right conditions, white light can even separate into the colours of the visible spectrum.

These effects form the basis of several important optical phenomena: refraction, reflection, transmission and dispersion. Although the terminology may sound complex, a simple light refraction experiment can make each concept much easier to understand.

Traditional triangular prisms are commonly used to demonstrate how white light bends and separates into a rainbow. Dichroic prism cubes work differently: their internal surfaces reflect and transmit selected colours, allowing red, green and blue light to interact in striking ways.

In this guide, you will learn how these two types of prisms work, try practical experiments with light and discover why changing the angle, material or light source can produce dramatically different results.

What Is Light Refraction?

Light refraction occurs when light passes from one transparent material into another and changes speed. This change in speed usually causes the light ray to bend.

For example, light travels at different speeds through air, water and glass. When a beam moves from air into glass at an angle, it changes direction at the boundary between the two materials. When it leaves the glass, its direction changes again.

A familiar example is a pencil placed in a glass of water. The pencil appears bent or displaced where it enters the water, even though it remains perfectly straight. This happens because light from the submerged part is refracted before reaching your eyes.

The amount of bending depends mainly on:

• the materials through which the light travels;
• the angle at which the light reaches the surface;
• the wavelength, or colour, of the light.

If light enters a transparent surface directly at a 90-degree angle, its speed changes, but its path may not appear to bend. At other angles, the change in direction becomes easier to observe.

This is why rotating a prism or changing the position of a light source can significantly alter the visible result. Even a small adjustment can create a different path through the glass and reveal new patterns of light and colour.

Reflection, Refraction and Transmission

When light reaches the boundary between two materials, it can behave in three principal ways: it may be reflected, refracted or transmitted. In many situations, these effects occur at the same time.

Reflection

Reflection happens when light strikes a surface and returns towards the material from which it came. A mirror produces a clear reflection, but glass, water and polished objects also reflect part of the light that reaches them.

The direction of the reflected light depends on the angle at which it strikes the surface. This is why rotating a prism can change the position and intensity of the colours you observe.

Refraction

Refraction occurs when light enters a different transparent material, changes speed and usually changes direction. A prism makes this bending easier to observe because its angled surfaces redirect the light as it enters and leaves the glass.

The amount of refraction depends on the material, the angle of incidence and the wavelength of the light.

Transmission

Transmission describes light passing through a material. Clear glass transmits much of the visible light that reaches it, although some light may also be reflected or absorbed.

In a dichroic prism cube, specially designed internal surfaces transmit certain wavelengths while reflecting others. This selective behaviour allows different colour components to follow separate paths inside the cube.

Understanding these three phenomena helps explain why the same optical object can produce different results when you change the light source, viewing position or angle:

• Reflection: light returns from a surface.
• Refraction: light bends as it enters or leaves another material.
• Transmission: light passes through a material.

Together, reflection, refraction and transmission create the changing patterns of light and colour observed in both traditional prisms and dichroic prism cubes.

How Does a Traditional Prism Create a Rainbow?

White light may look colourless, but it contains many wavelengths that our eyes perceive as different colours. When white light passes through a traditional triangular prism, these wavelengths are refracted by slightly different amounts.

This separation of colours is called dispersion.

Violet and blue light generally bend more than red and orange light because each wavelength travels through glass at a slightly different speed. As the separated light leaves the prism, it forms a visible spectrum commonly recognised as:

• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet

The quality of the rainbow depends on several factors:

• the angle at which the light enters the prism;
• the shape and optical quality of the prism;
• the brightness and width of the light beam;
• the distance between the prism and the viewing surface;
• the amount of ambient light in the room.

A narrow beam of white light usually produces a clearer spectrum than a broad or diffused source. Positioning a white sheet of paper or wall behind the prism can also make the colours easier to observe.

It is important to distinguish this process from the behaviour of a dichroic prism cube. A traditional prism creates a spectrum primarily through refraction and dispersion. A dichroic cube uses coated internal surfaces to selectively reflect and transmit colour components.

Both devices create fascinating optical effects, but they demonstrate different properties of light.

Light Refraction Experiment with a Prism

A simple prism experiment makes it possible to observe how white light changes direction and separates into visible colours. For the clearest result, use a traditional triangular prism, since this shape is specifically suited to demonstrating refraction and dispersion.

Materials You Will Need

• A triangular glass or acrylic prism
• A narrow beam of white light
• A white sheet of paper or plain white wall
• A darkened room
• Books, modelling clay or another stable support
• An adult supervisor when working with younger students

Step-by-Step Instructions

1. Darken the room enough to make projected colours easy to see.
2. Place the prism on a stable surface near the white paper or wall.
3. Direct a narrow beam of white light towards one angled face of the prism.
4. Slowly rotate the prism until a spectrum appears on the viewing surface.
5. Adjust the distance between the prism and the surface to improve the separation and clarity of the colours.
6. Observe how the position, width and intensity of the spectrum change when you alter the angle of the prism or light source.

What Should You Observe?

As the white light enters the prism, it slows down and bends. Its different wavelengths are refracted by slightly different amounts, causing the light to separate into a visible spectrum.

You may notice that:

• red light bends less than blue or violet light;
• small changes in angle move the spectrum significantly;
• a narrow, bright beam produces clearer colour separation;
• increasing the projection distance can spread the colours further apart;
• excessive ambient light makes the spectrum harder to see.

Questions to Explore

• What happens when the prism is rotated?
• Does the spectrum change when the light source moves?
• Which colour appears to bend the most?
• How does the distance from the paper affect the result?
• Does glass produce a clearer spectrum than acrylic?
• What happens when you use coloured light instead of white light?

Record the setup and observations after each change. Altering only one variable at a time makes it easier to understand which factor affected the result.

Important distinction: This experiment requires a traditional triangular prism. A dichroic prism cube such as PrismLab™ is better suited to exploring RGB colour interaction, reflection and transmission, which we will examine later in this guide.

Why Do Different Colours Bend Differently?

Visible light contains a range of wavelengths. Our eyes interpret these wavelengths as different colours, from longer-wavelength red light to shorter-wavelength violet light.

When light enters glass, each wavelength interacts with the material slightly differently. As a result, the colours travel through the glass at slightly different speeds and are refracted by different amounts.

In a traditional prism:

• Red light generally bends the least.
• Orange and yellow light bend slightly more.
• Green light appears near the middle of the spectrum.
• Blue and violet light generally bend the most.

This wavelength-dependent behaviour is known as dispersion. It explains why white light spreads into a spectrum instead of leaving the prism as a single white beam.

The Role of the Refractive Index

The refractive index describes how much light slows down when travelling through a material compared with its speed in a vacuum. Glass does not have exactly the same refractive index for every wavelength.

Shorter wavelengths, such as blue and violet, usually experience a slightly higher refractive index in glass than longer wavelengths such as red. They therefore change direction more strongly when entering and leaving the prism.

The difference may be small at each surface, but the angled faces of a triangular prism make the separation visible.

Why the Angle Matters

The angle at which light enters the prism also affects the result. Rotating the prism changes the path travelled by each wavelength and the direction in which the separated colours emerge.

This is why a rainbow may suddenly appear, become wider or disappear entirely after only a small adjustment. The colours remain present in the white light, but the correct alignment is needed to project them clearly onto a surface.

Refraction Is Not the Same as Colour Filtering

A traditional prism separates wavelengths through refraction and dispersion. It does not create the colours or selectively remove them.

A dichroic prism cube works differently. Its coated internal surfaces are designed to reflect certain wavelength ranges while transmitting others. Rather than producing a continuous rainbow through dispersion, it separates and redirects selected colour components—commonly red, green and blue.

Understanding this distinction prepares us to explore how a dichroic prism cube works and why its optical effects differ from those of a traditional triangular prism.

What Is a Dichroic Prism Cube?

A dichroic prism cube is an optical component formed by precisely joined glass prisms with specially coated surfaces inside. These internal coatings selectively reflect certain ranges of visible light while allowing others to pass through.

Unlike a traditional triangular prism, which separates white light into a continuous spectrum through refraction and dispersion, a dichroic prism cube separates or combines selected colour components—typically red, green and blue.

How Do the Internal Surfaces Work?

Dichroic coatings consist of extremely thin optical layers designed to interact differently with specific wavelengths. When light reaches a coated surface:

• certain colour components are reflected;
• other colour components are transmitted;
• the direction and visible result depend on the angle of the light;
• rotating the cube changes which internal reflections are visible to the observer.

This selective behaviour can create distinct red, green and blue regions, overlapping colours and changing patterns inside the cube.

Why Are Red, Green and Blue Used?

Red, green and blue are the primary colours of additive light. When combined at different intensities, they can produce many other visible colours:

• Red + green can appear yellow.
• Green + blue can appear cyan.
• Red + blue can appear magenta.
• Red + green + blue can appear white when balanced correctly.

A dichroic prism cube therefore provides a practical way to explore how coloured light can be separated, redirected and recombined.

Where Are Dichroic Prism Cubes Used?

Similar optical systems are used in technologies that need to manage colour precisely, including:

• projectors;
• cameras and imaging systems;
• scientific instruments;
• optical demonstrations;
• laboratory and classroom experiments.

The compact PrismLab™ Optical Prism Cube makes these principles accessible through direct observation. By rotating the cube, changing the viewing position and adjusting the light source, students and science enthusiasts can explore RGB colour interaction, reflection and transmission in a hands-on format.

Traditional Prism vs Dichroic Prism Cube

Traditional triangular prisms and dichroic prism cubes can both produce captivating colour effects, but they interact with light in different ways. Understanding this distinction helps you select the correct optical instrument for each experiment.

Traditional Triangular Prism

A traditional prism uses its angled transparent surfaces to refract light. Because different wavelengths bend by slightly different amounts, white light can separate into a continuous visible spectrum.

It is particularly suitable for exploring:

• refraction;
• dispersion;
• the visible spectrum;
• rainbow formation;
• how different wavelengths bend;
• the effect of changing the angle of incidence.

Its characteristic result is a band of colours ranging from red to violet.

Dichroic Prism Cube

A dichroic prism cube contains internal optical coatings that selectively reflect and transmit particular wavelength ranges. It commonly separates or combines red, green and blue components rather than producing a continuous rainbow through dispersion.

It is particularly suitable for exploring:

• reflection and transmission;
• RGB colour separation;
• additive colour interaction;
• internal optical pathways;
• changes caused by rotation and viewing angle;
• the recombination of coloured light.

Its characteristic result is a changing arrangement of distinct RGB colours and their combinations.

Key Differences

Which Prism Should You Use?

Choose a traditional triangular prism when your objective is to split white light into a rainbow or investigate how different wavelengths refract.

Choose a dichroic prism cube when you want to observe how selected colour components are reflected, transmitted and recombined inside an optical system.

Neither instrument is inherently better than the other. Each demonstrates a different part of light science. Using both allows students to compare dispersion with colour filtering and develop a more complete understanding of optical behaviour.

RGB Light Experiment with PrismLab™

The PrismLab™ Optical Prism Cube allows you to investigate how its internal dichroic surfaces reflect and transmit different colour components. Unlike the traditional prism experiment, the objective is not to project a continuous rainbow, but to observe how RGB colours change with light, rotation and viewing angle.

Materials You Will Need

• A PrismLab™ Optical Prism Cube
• A white LED torch or another steady white light source
• Optional red, green and blue LED lights
• A white sheet of paper
• A darkened room
• A stable table or work surface

Experiment 1 — Explore the Cube with White Light

1. Place the cube on a white sheet of paper.
2. Direct a white light towards one face of the cube.
3. Look through the cube from different sides without staring directly into the light source.
4. Slowly rotate the cube and observe how the red, green and blue regions change position and intensity.
5. Adjust the angle and distance of the light to reveal different internal reflections.

You may observe distinct coloured surfaces, overlapping hues and changing optical pathways. The result depends on the light source, angle of incidence, cube orientation and viewing position.

Experiment 2 — Compare Different Light Angles

Keep the cube in the same position and direct the light towards it from several angles. Record what changes after each adjustment.

Consider these questions:

• Which colours appear most clearly?
• Does one face reflect more light than another?
• Which colours remain visible through the cube?
• What happens when the light reaches an internal surface at a steeper angle?
• Do the patterns change when you view the cube from the opposite side?

Changing only the light angle helps isolate its effect on the visible result.

Experiment 3 — Test Coloured Light

If red, green and blue LED lights are available, illuminate the cube with one colour at a time.

Compare how each colour is reflected or transmitted through the internal surfaces. Then try two light colours together and observe whether their paths overlap.

Under suitable conditions, additive colour combinations may appear:

• Red + green can produce yellow.
• Green + blue can produce cyan.
• Red + blue can produce magenta.
• Balanced red, green and blue light can appear white.

The exact result will depend on the direction, brightness and alignment of the light sources.

Record Your Observations

Create a simple table containing:

• the light source used;
• the angle of the light;
• the viewing position;
• the cube orientation;
• the colours observed;
• any overlapping or reflected patterns.

Photographs can help compare different setups, but direct observation may reveal colour and depth effects that a camera does not reproduce accurately.

What Does the Experiment Demonstrate?

These activities show that the cube’s appearance is not fixed. Its internal coatings interact selectively with different wavelength ranges, while rotation and viewing angle determine which reflected and transmitted paths reach your eyes.

PrismLab™ therefore provides a compact way to investigate:

• selective reflection;
• light transmission;
• RGB colour separation;
• additive colour interaction;
• internal optical pathways;
• the relationship between light angle and visible colour.

Safety note: Never direct a laser or other intense light source towards anyone’s eyes. Handle the glass cube carefully and conduct the experiment over a stable surface.

Educational Benefits of Hands-On Optics

Optics becomes easier to understand when students can directly change a setup and observe the result. Instead of treating reflection, refraction and transmission as abstract definitions, hands-on experiments turn them into visible phenomena.

Makes Abstract Concepts Visible

Light cannot normally be observed travelling through air, but its effects become visible when it interacts with glass and optical surfaces. A prism experiment helps students connect scientific terminology with real observations:

• a redirected beam demonstrates refraction;
• light returning from a surface demonstrates reflection;
• light continuing through glass demonstrates transmission;
• separated colours reveal dispersion or selective wavelength behaviour.

Develops Scientific Thinking

Prism experiments encourage students to ask questions, make predictions and test one variable at a time. They can change the light angle, viewing position, distance or prism orientation and compare the results.

This process develops important scientific habits:

• careful observation;
• hypothesis formation;
• controlled experimentation;
• comparison of results;
• recording evidence;
• explaining cause and effect.

Encourages Curiosity and Independent Exploration

There is no single fixed view inside a dichroic prism cube. Every change in angle can reveal a different colour, reflection or internal pathway. This encourages learners to explore independently and investigate why the result changed.

Unexpected outcomes also become valuable. If a colour disappears or a reflection moves, students can adjust the setup and search for an explanation.

Connects Science with Everyday Technology

The principles demonstrated by prisms are used in cameras, projectors, scientific instruments and other optical systems. Exploring them helps students understand that light science is not limited to a classroom experiment—it also supports technologies they encounter in everyday life.

Supports Screen-Free STEM Learning

Hands-on optics provides a focused activity built around a physical object, a light source and direct observation. Students actively manipulate the experiment rather than passively watching a demonstration on a screen.

A traditional triangular prism and a dichroic cube such as PrismLab™ offer complementary learning experiences. Together, they help learners compare dispersion with selective reflection and transmission, creating a broader and more accurate understanding of how light behaves.

Choosing the Right Prism for Your Experiment

The best prism depends on the optical phenomenon you want to observe. Traditional triangular prisms and dichroic prism cubes serve different purposes, so defining the objective of the experiment should always come first.

Choose a Traditional Triangular Prism When You Want To:

• split white light into a visible rainbow;
• investigate refraction and dispersion;
• compare how different colours bend;
• study the visible spectrum;
• observe how the angle of incidence changes the projected result.

For the clearest spectrum, use a narrow beam of white light, a darkened room and a white projection surface.

Choose a Dichroic Prism Cube When You Want To:

• explore selective reflection and transmission;
• observe red, green and blue colour components;
• investigate additive colour interaction;
• examine internal optical pathways;
• compare results from different viewing angles;
• understand how optical coatings manage light.

A dichroic cube such as PrismLab™ Optical Prism Cube is especially suitable for compact, hands-on RGB light experiments.

Consider the Material

Glass prisms generally provide clear optical results and greater resistance to surface scratching, but they must be handled carefully. Acrylic prisms are lighter and may be more suitable for younger learners, although their optical clarity and scratch resistance can vary.

PrismLab™ is made from K9 optical glass and is therefore intended for careful use by students aged 14+, educators and science enthusiasts.

Consider the Size

Larger prisms are usually easier to position and may be more suitable for group demonstrations. Smaller optical components are portable and convenient for close observation, but their dimensions should be checked carefully before purchase.

PrismLab™ is available in 12.7 mm and 15 mm sizes. Both versions are miniature optical instruments designed to fit between your fingertips.

Match the Tool to the Learning Objective

Choosing the correct prism makes the experiment clearer and prevents misleading conclusions. A triangular prism is the appropriate tool for rainbow dispersion, while a dichroic cube is designed for exploring RGB colour interaction, reflection and transmission.

Safety and Experiment Tips

Prism experiments are simple to perform, but careful handling and an appropriate light source are essential. The following precautions help protect both the user and the optical instrument.

Handle Glass Prisms Carefully

Glass prisms can be damaged if dropped or struck against a hard surface. Always:

• work over a stable table;
• keep the prism away from table edges;
• hold it securely without applying excessive pressure;
• store it in its protective pouch when not in use;
• stop using it if the glass becomes chipped or cracked.

Because PrismLab™ is a miniature K9 optical glass component, it is recommended for users aged 14+ and should be handled carefully.

Protect the Optical Surfaces

Fingerprints, dust and scratches can reduce the clarity of the observed effects.

Hold the prism by its edges whenever possible. If cleaning is necessary, use a clean microfibre lens cloth. Avoid abrasive fabrics, household cleaning products and rough paper towels.

Use Safe Light Sources

A standard white LED torch is suitable for most experiments. Coloured LEDs can also be used when exploring RGB interaction.

Never:

• look directly into a bright light source;
• direct the light towards another person’s eyes;
• use high-powered lasers;
• focus intense sunlight through the prism;
• leave powerful lamps close enough to heat the glass.

Create a Stable Experiment Area

A darkened room can improve colour visibility, but the working area should remain safe and organised. Keep cables, lamps and other materials secure, and leave enough light to move around without difficulty.

A white sheet of paper provides a simple background for observing reflected, transmitted or dispersed light.

Change One Variable at a Time

For clearer observations, adjust only one part of the setup during each test:

• rotate the prism;
• move the light source;
• change the viewing position;
• adjust the distance;
• test a different colour of light.

Recording each change makes it easier to identify what caused a new colour, reflection or optical pathway to appear.

Keep Expectations Realistic

The visible result depends on the type of prism, light source, viewing angle and surrounding brightness. A triangular prism requires suitable alignment to project a clear spectrum, while a dichroic cube produces RGB reflections and transmissions that change with perspective.

Cameras may also reproduce colours differently from the human eye. The most accurate way to explore the effect is through careful direct observation.

Following these precautions creates a safer experiment and helps preserve the prism’s optical quality for future investigations.

Turn Light into a Hands-On Discovery

Light becomes far easier to understand when its behaviour can be observed directly. A simple change in angle, material or viewing position can reveal refraction, reflection, transmission, dispersion and colour interaction.

Traditional triangular prisms demonstrate how white light bends and separates into a continuous spectrum. Dichroic prism cubes provide a different experience, selectively reflecting and transmitting colour components to reveal changing RGB patterns and internal optical pathways.

Neither instrument replaces the other. Together, they demonstrate complementary principles and help students understand why different optical systems produce different results.

With a suitable light source and a carefully prepared experiment, learners can:

• observe scientific concepts rather than simply read about them;
• compare dispersion with selective colour separation;
• test how angles affect visible results;
• record evidence and investigate cause and effect;
• connect classroom science with real optical technologies;
• enjoy focused, screen-free STEM exploration.

The PrismLab™ Optical Prism Cube brings RGB light interaction, reflection and transmission into a compact hands-on format. Designed for students aged 14+, educators and science enthusiasts, it transforms a small optical instrument into an open invitation to experiment, observe and discover.

The most valuable part of any light experiment is not simply the colour that appears—it is understanding why it changed.

Frequently Asked Questions

What is a light refraction experiment?

A light refraction experiment demonstrates how light changes speed and usually bends when it passes from one transparent material into another, such as from air into glass or water. Prisms are especially useful because their angled surfaces make this change in direction easier to observe.

How does a prism create a rainbow?

A traditional triangular prism refracts different wavelengths of white light by slightly different amounts. This process, called dispersion, separates the light into a continuous visible spectrum ranging from red to violet.

What is the difference between refraction and dispersion?

Refraction is the change in direction that occurs when light passes between materials. Dispersion happens when different wavelengths are refracted by different amounts, causing white light to separate into its component colours.

Is a dichroic prism cube the same as a traditional prism?

No. A traditional triangular prism primarily uses refraction and dispersion to separate white light into a rainbow. A dichroic prism cube contains coated internal surfaces that selectively reflect and transmit colour components, commonly red, green and blue.

Does PrismLab™ produce a traditional rainbow?

PrismLab™ is not designed to produce the same continuous rainbow spectrum as a triangular prism. Its dichroic internal surfaces create distinct RGB reflections, transmissions and colour combinations that change with the light source, cube orientation and viewing angle.

What light source should I use with PrismLab™?

A steady white LED torch is suitable for general observation. Red, green and blue LED lights can also be used to explore selective reflection, transmission and additive colour interaction. High-powered lasers and other intense light sources should not be used.

Why do the colours change when the cube rotates?

Rotating the cube changes the angle at which light reaches its internal dichroic surfaces and the paths that reflected and transmitted light take towards the observer. This reveals different colours, intensities and internal patterns.

Can children use PrismLab™?

PrismLab™ is recommended for users aged 14+, educators and science enthusiasts. It is a miniature optical instrument made from K9 glass and should be handled carefully over a stable surface. Younger learners should use age-appropriate optical materials under responsible adult supervision.

What size is PrismLab™?

The PrismLab™ Optical Prism Cube is available in 12.7 mm and 15 mm versions. Both are miniature optical components designed to fit between the fingertips, so the selected dimensions should be checked carefully before ordering.

How should an optical prism cube be cleaned?

Hold the cube by its edges whenever possible and remove fingerprints or dust with a clean microfibre lens cloth. Avoid abrasive materials, rough paper towels and household cleaning products that could damage the optical surfaces.

What can students learn from prism experiments?

Prism experiments can help students understand refraction, reflection, transmission, dispersion, RGB colour interaction and additive colour mixing. They also develop observation, hypothesis formation, controlled experimentation and evidence-recording skills.

Which prism is best for a science experiment?

It depends on the learning objective. Choose a triangular prism to study rainbow formation, refraction and dispersion. Choose a dichroic prism cube to explore RGB colour separation, selective reflection, transmission and changing internal optical pathways.