Light Waves

Light Behaves Like a Wave, With One Big Twist

Light bounces, bends, and can be blocked or absorbed just like the mechanical waves you explored with springs and ripple tanks. Shine a flashlight at a mirror and it reflects straight back at you, following the exact same rules of reflection as a wave bouncing off the edge of a ripple tank. Shine it through a glass of water and you'll see it refract, bending as it crosses from air into water because light slows down when it enters a denser material.

But light has one enormous difference from sound: it doesn't need a medium at all. Sound needs air, water, or a solid to travel through, which is why there's no sound in the vacuum of space. Light, however, is an electromagnetic wave — a wave made of vibrating electric and magnetic fields, not vibrating matter — so it travels just fine through the emptiness of space. That's exactly how sunlight crosses 93 million miles of empty space to warm your face.

Absorption, Reflection, and Refraction in Everyday Materials

What happens when light hits an object depends on both the frequency of the light and the material it hits. A red shirt looks red because the fabric absorbs every color of light except red, which it reflects back to your eyes. A clear glass window lets most light pass straight through (transmission), while a mirror is built to reflect almost all of it. Black pavement gets scorching hot on a sunny day because dark materials absorb most light energy and convert it into heat instead of reflecting or transmitting it.

Engineers exploit these behaviors on purpose. Sunglasses use tinted materials that absorb certain frequencies of light to protect your eyes. Camera and eyeglass lenses are precisely curved pieces of glass that refract light in controlled ways to focus an image. Mirrors are coated with reflective metal to bounce nearly all light back. Even soundproofing foam in a recording studio is chosen because its bumpy shape and soft material absorb sound waves instead of reflecting them around the room, showing that the same principles — reflection, absorption, and transmission — apply across totally different types of waves.

One Rainbow, One Giant Spectrum

When white light passes through a prism, it splits into a rainbow of colors — red, orange, yellow, green, blue, indigo, and violet. Each color you see is really just visible light at a different frequency and wavelength: red has the longest wavelength and lowest frequency of visible light, while violet has the shortest wavelength and highest frequency. But that rainbow is only a tiny sliver of something much bigger: the electromagnetic spectrum.

The electromagnetic spectrum includes every type of electromagnetic wave, from radio waves with wavelengths longer than a football field, through microwaves, infrared, visible light, ultraviolet, and all the way to X-rays and gamma rays with wavelengths smaller than an atom. Every single one of these is fundamentally the same kind of wave as visible light — just at a different frequency. Higher-frequency EM waves carry more energy, which is why X-rays can pass through soft tissue to photograph your bones, while low-frequency radio waves can safely pass through walls carrying nothing more than a Wi-Fi signal.

Society uses different parts of this spectrum constantly: microwave ovens vibrate water molecules in food to cook it, infrared cameras detect body heat in the dark, ultraviolet light disinfects water and hospital equipment, and radio waves broadcast everything from music stations to the signal your phone uses to make a call. You're surrounded by invisible waves nearly every moment of your life.