The Rainbow Reflector: Light Refraction and Prisms (#96)
Experiment at a Glance
Recommended Age: 6–12 years
Estimated Cost: Under $2
Difficulty Level: Easy
Time Required: 15 minutes
Can You Really Make a Rainbow With Just Water and a Mirror?
Yes, absolutely! You can create a brilliant rainbow using nothing more than a shallow dish of water, a small mirror, and sunlight streaming through your window. When white light passes through water at an angle and bounces off a mirror, it breaks apart into all the colors hiding inside, red, orange, yellow, green, blue, indigo, and violet. This simple setup turns your kitchen or classroom into an optical physics laboratory, proving that everyday items can reveal the invisible science happening all around us.
This experiment, number 96 in our series of 100 hands-on science adventures, shows kids exactly how prisms work without needing an expensive glass prism. The water acts as your prism, bending (or "refracting") light at different angles depending on each color's wavelength. It's the same reason we see rainbows after rainstorms: millions of water droplets in the air each act like tiny prisms, splitting sunlight into a colorful arc across the sky.
The Science Behind the Spectrum
Light looks white to our eyes, but it's actually made of every color mixed together. Scientists call this "white light," and it travels in waves. Each color has a different wavelength, red has the longest, violet has the shortest, and all the others fall somewhere in between.
When light moves from one material (like air) into another material (like water), it slows down and bends. This bending is called refraction. Here's the clever part: different wavelengths bend at slightly different angles. Red bends the least, violet bends the most, and all the other colors spread out between them. That's why you see a rainbow instead of just white light on the other side.
A mirror in the water setup does double duty. First, the light refracts when it enters the water. Then it bounces off the mirror (that's reflection), travels back through the water (refracting again), and exits into the air at an angle that projects all those separated colors onto your wall or ceiling. Two refractions plus one reflection equals one spectacular rainbow.
This is the same principle behind glass prisms, raindrops in the atmosphere, and even the shimmer you see in soap bubbles or oil slicks on puddles. Anytime light passes through a transparent material at an angle, you get a chance to see its hidden colors.
What You'll Need
Gather these simple materials before you start:
- One small pocket mirror (the kind you'd keep in a purse or backpack)
- One shallow dish or small baking pan (clear glass works best, but any dish will do)
- Clean tap water
- A sunny window or bright flashlight (sunlight works better)
- A white wall or piece of white poster board to catch your rainbow
- Optional: a dark room or dim lighting to make your rainbow more vivid
Everything else is just positioning and patience. No special equipment, no fancy glassware, no expensive prisms from a science supply catalog.
Step-by-Step Instructions
Step 1: Set Up Your Station
Choose a sunny window where bright, direct sunlight streams in. Morning or late afternoon light works beautifully because the sun sits lower in the sky, making it easier to angle your setup. Fill your shallow dish about halfway with water, you want enough water to submerge part of the mirror, but not so much that the mirror floats around.
Step 2: Position the Mirror
Place the mirror inside the dish at an angle, leaning it against one side so that part of it sits underwater and part sticks up above the surface. The mirror should face the sunlight coming through the window. Think of it like a tiny ramp half-submerged in a pool.
Step 3: Find Your Rainbow
Adjust the angle of the mirror slowly until sunlight hits it, passes through the water, and reflects onto a nearby white wall or ceiling. You might need to shift the dish slightly or change the mirror's tilt. When you get the angle just right, you'll see a rainbow appear on your wall, red on one edge, violet on the other, with all the colors in between.
Step 4: Experiment With Angles
Once you've found your rainbow, try moving the dish closer to or farther from the wall. Notice how the rainbow changes size. Tilt the mirror at different angles and watch the colors shift position. If you're using a flashlight instead of sunlight, move the light source around to see how that affects your results.
Step 5: Catch It on Paper
Hold up a piece of white poster board or cardboard to "catch" the rainbow in midair. Move the paper closer to the dish and farther away. You'll see the rainbow grow larger and dimmer as you move farther, or smaller and brighter as you move closer.
What's Actually Happening Here
When sunlight enters the water at an angle, it slows down and bends, that's your first refraction. The light travels through the water and hits the mirror, which reflects it back. Then the light exits the water and bends again as it returns to air, your second refraction. Those two bending events, combined with the reflection, spread the different wavelengths of light apart enough that your eyes can see them as separate colors.
Think of it like runners in a relay race entering a thick mud pit. The fastest runners (red light) slow down the least and take a straighter path. The slowest runners (violet light) get bogged down more and veer off at a sharper angle. By the time they all exit the mud pit, they're spread out in a line instead of bunched together.
The reason you need the mirror isn't just to bounce the light back, it's to create a longer path through the water. More distance through the water means more bending, which means more separation between colors. Without the mirror, light would pass through the water too quickly and the colors wouldn't spread apart enough for you to see them distinctly.
Frequently Asked Questions
Why doesn't my rainbow show all the colors clearly?
If your rainbow looks washed out or you only see a few colors, try these fixes: Make sure you're using direct sunlight rather than light filtered through clouds or curtains. Dim the room lights to reduce competing light sources. Use a shallower dish so the water layer is thinner and cleaner. Check that your wall or paper is white, not cream or off-white, which absorbs some colors better than others.
Can I do this experiment without sunlight?
Yes, but you'll get better results with a very bright LED flashlight or phone light. Point the light at the mirror-and-water setup from the same angle sunlight would hit it. You might need to hold the light steady for a minute or two while you adjust the mirror position. The rainbow will be fainter than with sunlight, but you'll still see the color separation clearly in a dark room.
Why does the order of colors never change?
The order stays the same: red, orange, yellow, green, blue, indigo, violet: because it's determined by the physics of wavelengths. Red light always has the longest wavelength, so it always bends the least. Violet light always has the shortest wavelength, so it always bends the most. The other colors fall in between based on their wavelengths. This order is universal; you'll see it in every rainbow, whether it's from a prism, a garden hose spray, or a rainstorm.
What if I see multiple faint rainbows?
Sometimes you'll notice a second, dimmer rainbow above or beside your main rainbow. That's caused by light reflecting multiple times inside the water before exiting, creating a "double bounce." The secondary rainbow will have its colors reversed (violet on top, red on bottom) because of the extra reflection. It's a bonus bit of optical physics to observe and discuss.
How is this different from using a glass prism?
A glass prism and your water setup both work through refraction, but a prism is designed with precise angles to maximize color separation in one pass. Your water dish requires the mirror to bounce light back through the water for a second refraction, which spreads the colors enough to see. The result is nearly identical: you're just using household items to replicate what an expensive piece of cut glass does naturally.
Take It Further
Once you've mastered the basic rainbow reflector, try these variations:
Add a drop of milk to the water. The tiny particles in milk scatter light differently, creating a milky glow and making the light path visible. You can actually see the beam of light traveling through the water before it splits into colors.
Use different colored lights. Shine a red flashlight, then a blue one, then a green one at your setup. Notice that colored light can't be split into a rainbow: it's already a single wavelength. Only white light (which contains all colors) can be separated into a spectrum.
Compare tap water to distilled water. Distilled water is purer and might give you a slightly sharper rainbow because there are fewer dissolved minerals to scatter the light.
Try different mirror sizes. A bigger mirror catches more light and might produce a larger, brighter rainbow. A tiny compact mirror forces you to be more precise with your angles but can still work beautifully.
Photograph your rainbow. Rainbows can be tricky to capture on camera, but if you succeed, you'll have a permanent record of your optical physics experiment. Use a fast shutter speed and turn off your camera's flash.
The Bigger Picture
This experiment connects to so much more than just rainbows on your wall. Every time light moves from one material to another: air to water, air to glass, even air to the surface of your eye: refraction is happening. That's why a straw looks bent when you stick it in a glass of water. It's why swimming pools look shallower than they really are. It's why eyeglasses can correct vision by bending light before it enters your eye.
Understanding refraction also helps explain atmospheric phenomena like mirages in the desert, the green flash at sunset, and why stars twinkle at night (hint: it's because starlight refracts through layers of moving air in Earth's atmosphere). Scientists use these same principles to design everything from camera lenses to fiber optic cables to telescopes that peer billions of light-years into space.
For kids, this experiment proves that physics isn't locked away in textbooks or laboratories: it's right there in your kitchen, waiting to be discovered with a mirror and a dish of water. The same light that's bouncing around your room right now contains every color of the rainbow. You just need to know how to persuade it to show itself.
Ready to explore more hands-on science? Check out our complete collection of experiments at Tierney Family Farms and discover 100 ways to turn your home into a learning laboratory.