Light Demonstrations

Light is a form of electromagnetic radiation that makes vision possible and interacts with matter in distinctive ways. This category looks at how light travels, reflects, refracts, and disperses, as well as how it can be absorbed or transmitted. Studying light helps connect physics to everyday experiences and technologies, from seeing colours to using optical instruments.

Demonstration	Materials	Difficulty	Safety	Summary
AC vs DC with a Bicolor LED	★★★	★★☆	★☆☆	A bicolor LED connected to a circuit shows the difference between AC and DC power. With DC, the LED glows red or green depending on polarity, while with AC it alternates between colors at 60 Hz. Swinging the LED in a circle makes the rapid switching visible as a multicolored light ring.
Focal Length of a Concave Lens	★★☆	★☆☆	★☆☆	A concave lens causes parallel rays of light from a light box to diverge. By extending the diverging rays backward, their virtual intersection point is located, which defines the principal focal point. Measuring the distance from this point to the center of the lens gives the focal length.
Burning Paper with a Convex Lens	★☆☆	★☆☆	★★☆	A convex lens is used to concentrate sunlight onto a small point on a piece of paper. The focused light intensifies the heat at the focal point until the paper ignites.
Focal Length of a Convex Lens	★★☆	★☆☆	★☆☆	A convex lens is used to converge parallel rays of light from a light box onto a screen. By adjusting the position of the screen until the sharpest focus is achieved, the distance from the lens to the focused spot gives the focal length of the lens.
Scattering of Light with Milk	★☆☆	★☆☆	★☆☆	A flashlight shining through water mixed with milk demonstrates how scattering of shorter wavelengths makes light appear blue from the side and red-orange when viewed through the length of the liquid, simulating why the sky is blue and sunsets are red.
Van de Graaff with Fluorescent Bulb	★★★	★★☆	★★★	A fluorescent light bulb can flicker and glow when brought near a Van de Graaff generator. The strong electric field from the charged dome excites the gas inside the bulb, demonstrating electrostatic discharge and how electric fields can cause visible light emission.
Color Changing Water	★☆☆	★☆☆	★☆☆	A glass of blue-colored water is placed inside a bowl, and the bowl is then filled with yellow-colored water. When looking through the bowl, the overlapping yellow and blue liquids appear green, even though the water in each container stays its original color.
Inverse Square Law with Light	★★☆	★☆☆	★☆☆	A lamp and light meter are used to show that illumination decreases with the square of the distance from the source. Students observe that doubling the distance reduces the light intensity to one quarter, demonstrating the inverse-square law.
Colour and Temperature of Stars	★★★	★★☆	★★☆	A lamp connected to a variable resistor demonstrates how the color of light changes with temperature, helping to explain why cooler stars appear red while hotter stars shine white or blue.
Flying Optical Illusion	★★★	★★☆	★☆☆	A large mirror creates the illusion that a person’s leg reflection is actually their other leg, making it appear as though both legs lift off the ground and the person is flying.
Total Internal Reflection in a Water Stream	★★☆	★★☆	★★☆	A laser beam is sent through a small hole in a water-filled bottle so it enters the flowing stream. The light undergoes total internal reflection and follows the curve of the stream, just like light in an optical fiber.
Laser Microscope	★★☆	★★☆	★★☆	A laser is focused through a water droplet at the tip of a syringe, which acts as a convex lens. The light is projected onto a screen, allowing small aquatic organisms and impurities in the water to be observed.
Investigating Refraction and Snell's Law	★★☆	★☆☆	★☆☆	A narrow beam of light is shone through a glass block at different angles. By measuring the angles of incidence and refraction, students can apply Snell’s Law and determine the refractive index of the glass.
Newton Disc - Spinning Color Wheel	★☆☆	★☆☆	★☆☆	A Newton Disc demonstrates how colors of the spectrum (red, orange, yellow, green, blue, and violet) blend together when spun rapidly, appearing as white light to the human eye.
Investigating the Law of Reflection	★★☆	★☆☆	★☆☆	A ray box is used to shine light at a plane mirror, and the angles of incidence and reflection are measured. The experiment demonstrates the law of reflection, which states that the angle of incidence equals the angle of reflection.
Slinky Waves	★☆☆	★☆☆	★☆☆	A stretched slinky can be used to model both longitudinal and transverse waves. By pushing or flicking one end of the slinky, students can see how wave energy travels through the coils.
Light Refraction – Arrow Changes Direction	★☆☆	★☆☆	★☆☆	An arrow drawn on paper appears to change direction when viewed through a water-filled glass. This effect occurs because light bends, or refracts, as it passes through different mediums.
LED Photocell	★★☆	★☆☆	★★☆	An LED connected to a voltmeter generates a measurable voltage when illuminated by certain colors of light. White and green light produce a reading, but red light does not, showing that photon energy depends on frequency rather than brightness - evidence of light behaving as particles.
Measuring the Speed of Light With a Microwave	★★☆	★★☆	★★☆	By heating a layer of marshmallows in a microwave without the rotating tray, you can observe melted spots that mark the peaks of a standing wave. Measuring the distance between these spots and combining it with the microwave’s frequency allows you to calculate the speed of light.
Color Changing Walking Water	★☆☆	★☆☆	★☆☆	Cups filled with colored water are connected by folded paper towels. The water climbs up the paper towels and travels into empty cups through capillary action. As the colors mix in the empty cups, a rainbow effect is created.
Cow Eye Dissection	★★★	★★☆	★★☆	Dissect a preserved cow eye to trace the path of light through cornea, pupil, lens, and vitreous to the retina, then identify the optic nerve, blind spot, and tapetum to connect structure with how vision works. Use the lens to form real images to demonstrate image formation and inversion.
Glow Sticks at Different Temperatures	★☆☆	★☆☆	★★☆	Glow sticks glow due to chemiluminescence, a chemical reaction that releases light. Cold slows the reaction, producing a dimmer glow, while heat speeds it up, making the glow brighter but shorter-lived.
Making Light by Rubbing Quartz	★★★	★☆☆	★☆☆	In a dark room, rub or strike two pieces of clear quartz together to produce brief flashes of light and a faint odor. This visible glow is triboluminescence - light emitted when crystals are stressed, fractured, or rubbed.
Colour Subtraction with Filters	★★☆	★☆☆	★☆☆	Light filters and surfaces selectively transmit, reflect, or absorb different colors of light. This subtraction of colors explains why objects and filtered images appear in certain colors or may even appear black if no light is reflected or transmitted.
Wireless Audio Transfer Using Laser Light	★★★	★★★	★★☆	Live audio is sent over a visible laser beam. A microphone signal modulates the laser; a light sensor (e.g., solar cell) converts the received light back to an electrical signal that is amplified and played on a speaker.
Pinhole Camera	★☆☆	★☆☆	★☆☆	Make a lightproof box with a tiny hole on one side and a translucent screen on the other to project an inverted real image of the outside scene. This hands-on build demonstrates how light travels in straight lines and why small apertures produce sharper images.
Disappearing Coin Trick (Refraction)	★☆☆	★☆☆	★☆☆	Placing a glass of water over a coin makes the coin appear to vanish. This happens because light bends, or refracts, when it travels from air into water, preventing light from the coin from reaching the viewer’s eyes.
Black Light Fluorescence	★★★	★★☆	★★☆	Shine an ultraviolet (UV) “black light” on common items to reveal fluorescence. Students observe which materials glow and test mixtures (such as vitamins with vinegar) to explore how UV excitation produces visible light.
Afterimage Illusion	★☆☆	★☆☆	★☆☆	Stare at a brightly colored image for a short time, then look at a blank white surface and observe a “ghost” image that appears in complementary colors. This activity demonstrates how cone cells adapt and how the opponent process in vision creates negative and positive afterimages.
Blind Spot	★☆☆	★☆☆	★★☆	Students use a simple card with a dot and an X to locate their blind spot. By covering one eye and moving the card at arm’s length, they observe how part of their vision disappears when light falls on the optic nerve instead of light-sensitive cells in the retina.
Inverse Square Law With Balloon	★☆☆	★☆☆	★☆☆	Students use an inflating balloon to model how light spreads out as distance from the source increases. By measuring how a square drawn on the balloon stretches with inflation, they visualize the inverse square law, which explains why spacecraft need larger solar panels when farther from the Sun.
Doppler Effect with Water Waves	★★☆	★★☆	★☆☆	The Doppler Effect can be modeled using water waves. When a source of ripples moves through still water, the wavefronts bunch up in front of the moving source and spread out behind, showing how relative motion affects wave frequency.
Double Slit Experiment with Light	★★★	★★☆	★★☆	The double slit experiment with light shows how photons exhibit both wave and particle properties. A monochromatic light source passing through two slits produces an interference pattern on a screen, even when photons are sent one at a time.
Glowstick Dissection	★★☆	★★☆	★★★	This demonstration explores the chemical reaction inside glowsticks by dissecting them and using their contents to create glowing artwork. Students learn about chemiluminescence and reaction rates while experimenting with color, brightness, and duration of glow.
Convex Lens Mirror Imaging	★★☆	★☆☆	★☆☆	This demonstration shows how convex lenses and concave mirrors can bend or reflect light rays to bring them to a focus and form real images on a screen.
Radiometer	★★☆	★★☆	★☆☆	This demonstration shows how light energy can be transformed into both thermal and mechanical energy using a radiometer. The black sides of the vanes absorb more light and heat up more than the white sides. Air molecules striking the heated black surfaces gain more energy and rebound with greater force than those striking the white sides, causing the vanes to spin. A partial vacuum inside the bulb reduces resistance, making the effect easier to see.
Three Polarizing Filters	★★☆	★☆☆	★☆☆	This demonstration shows that two crossed polarizers block all light, but inserting a third polarizer at 45° between them transmits light - an effect explained by polarization, state preparation, and superposition. It offers an accessible, visual introduction to quantum ideas using classical optics.
Glowing Oobleck	★★☆	★☆☆	★☆☆	This Halloween-themed activity creates glowing oobleck that behaves like both a liquid and a solid. Under a blacklight, the quinine in tonic water makes the mixture glow eerily, and when placed on a speaker playing spooky music, the oobleck appears to writhe and dance like a haunted slime.
Color Mixing and Shadows	★★☆	★★☆	★★☆	Using red, green, and blue light sources aimed at a shadow screen, students explore how shadows change color and how overlapping beams of light combine to create new colors. The activity demonstrates that the primary colors of light (red, green, and blue) mix differently than paint pigments.
Glowing Pickle	★★★	★★★	★★★	When an electric current passes through a pickle, ions in the salty brine conduct electricity, exciting sodium atoms that emit a bright yellow glow. This demonstrates ionic conduction, atomic emission spectra, and electrolysis.
Luminol Chemiluminescence	★★★	★★☆	★★☆	When luminol is mixed with hydrogen peroxide in the presence of sodium hydroxide and potassium ferricyanide, a blue glow is produced. This reaction demonstrates chemiluminescence, where chemical energy is converted directly into light energy without heat.
Disappearing Glassware	★☆☆	★☆☆	★☆☆	When Pyrex glass is placed in vegetable oil, it becomes nearly invisible because both materials have the same refractive index.
Separating White Light into Colors	★★☆	★☆☆	★☆☆	When white light passes through a triangular prism, it separates into its component colors (red, orange, yellow, green, blue, violet). This occurs because each wavelength of light refracts, or bends, by a different amount as it enters and exits the prism.

Materials
★☆☆ Easy to get from supermarket or hardware store
★★☆ Available in most school laboratories or specialist stores
★★★ Requires materials not commonly found in school laboratories

Difficulty
★☆☆ Can be easily done by most teenagers
★★☆ Available in most school laboratories or specialist stores
★★★ Requires a more experienced teacher

Safety
★☆☆ Minimal safety procedures required
★★☆ Some safety precautions required to perform safely
★★★ Only to be attempted with adequate safety procedures and trained staff