Visible light is the light humans see with their eyes. Visible light comes primarily from the sun, but also from other natural and manmade light sources. The visible light spectrum is the range of wavelengths that make up visible light.
TL;DR (Too Long; Didn't Read)
Visible light is the kind of light that humans can see. Visible light travels incredibly fast, consists of a broad range of wavelengths and exists both as waves and particles.
What Is Light Made Of?
Light is a type of energy made of electromagnetic waves, a blend of magnetism and electricity. Visible light is only one kind of light, or electromagnetic radiation. Certain animals like bees can see other forms of light, such as ultraviolet light. Radio waves are another type of light, as is infrared light. Humans can only see a small section of electromagnetic radiation, and this band is called the visible light spectrum. Visible light is made both of waves and of particles. This idea is called “wave-particle duality” and is one of the basic tenets of the revolutionary physics discoveries in quantum theory.
When atoms are excited, they can emit a photon particle if another photon with the same energy passes by it.
Properties of Visible Light
The light that humans see with eyes is called visible light. Visible light contains every color that humans can see. There are distinct properties of visible light that set it apart from other types of electromagnetic radiation.
If the visible light spectrum passes through a prism, the resulting rainbow reveals all the colors in the spectrum. These range from red, with a wavelength of 700 nanometers (which is incredibly small), through orange, yellow, green, blue and finally violet, with a wavelength of 380 nanometers (which is even smaller!). Radio wavelengths, in contrast, are quite long, greater than a meter. Gamma ray wavelengths are even smaller than visible light wavelengths, at the picometer level!
One of the properties of visible light is the presence of dark absorption lines in the visible light spectrum. These lines serve as markers for missing wavelengths. Scientists use these patterns to study the makeup of stars, as missing wavelengths correspond to certain elements.
An interesting characteristic of visible light is that exists as both a wave and a particle. This may sound strange, but consider first the wave aspect of visible light. Like any other wave, including waves in the ocean, light waves can travel in every direction, interact with other waves and even bend.
These waves travel at 186,000 miles per second in a vacuum, which is referred to as one light second. Visible light does slow down when passing through denser material such as air or human eyes.
Visible light cannot pass through any opaque walls, like radio waves can.
Sources of Visible Light
Visible light can be emitted from a number of sources. The most influential visible light source on Earth is the sun. Other sources of visible light include stars, planets and moons (which display light reflected from the sun), auroras, meteors, volcanoes, lightning, fire and bioluminescent organisms such as fireflies, certain jellyfish, fish and even certain microbes.
Can you imagine living in an era without light bulbs or lamps? The technology of human light sources has evolved a great deal since early humans had to rely only on the light in their environment. Artificial sources of visible light include candles, oil lamps, gas lighting and light bulbs. Today, a broad range of light bulbs and lamps exist, from the early types of incandescent light bulbs to fluorescent lights, to light-emitting diode (LED) lights. More energy-efficient light bulbs are being made every year.
Another powerful source of length is the LASER, or Light Amplification by the Stimulated Emission of Radiation. At this point in time, lasers do not resemble the weapons seen in science fiction movies and television shows. But they are still very useful. Laser beams are single-wavelength light beams that are used in many modern technologies, from bar codes and music storage to surgery and microscopy. Laser altimeters are also being used by satellites used to study the Earth’s polar ice sheets, to see how much water they store. Light is constantly being used in new, efficient ways to help humanity, and indeed the entire world.
Color Components of Visible Light
Do you remember your first box of crayons? The joy of seeing so many colors in a little box meant so many possibilities! Maybe the most fascinating characteristic of visible light is color. Humans see a broad range of colors in visible light, and each color has its own corresponding wavelength. The color components of visible light include violet, blue, green, yellow to orange, bright red and dark red. The full range of visible light wavelength stretches from about 340 nanometers to around 750 nanometers. Light in the range of 340 to 400 nanometers is near ultraviolet (UV), mostly invisible to human eyes. Violet color consists of wavelengths from 400 to 430 nanometers. Blue’s wavelength range is 430 to 500 nanometers, and green’s is 500 to 570 nanometers. Yellow to orange colors range between 570 to 620 nanometers. Bright red has a wavelength ranging from 620 to 670 nanometers. Dark red’s wavelength is between 670 to 750 nanometers. Beyond this, near infrared light is over 750 nanometers, and beyond 1,100 nanometers is no longer visible to human eyes. At that point, light is in the infrared (IR) spectrum. If you want to see what IR light looks like, you can use an infrared camera, which picks up the light as heat signatures. As the sun sets, you may notice different colors than you would see if the sun were directly overhead. This is because the atmosphere of Earth serves as a kind of prism, and it bends the colors of the sunlight.
While blue is often considered a “cool color,” it can actually represent a very hot object, such as the blue flame on a gas stove, or a hot star. Yes, stars have colors! The star colors correspond to the temperature of the star. The sun is yellow in color and has a surface temperature of about 5,500 degrees Celsius. A cooler star like Betelgeuse, however, is red in color, at about 3,000 degrees Celsius. The hottest stars are blue, like Rigel, which is as hot as 12,000 degrees Celsius.
Without the color components of visible light, people could not appreciate the bright red color of strawberries, or the many hues of a sunset. Color gives people information about their world as well as beauty.
How People See Visible Light
Since the visible light spectrum is the light that humans can see, how does that work? The human eye and the brain work together to perceive visible light. Either there needs to be a light source, such as sunlight or a light bulb, or there needs to be reflected light on an object. Examples of reflected light include the light reflected from snow, ice and clouds. Light from any source enters the human eye and is received by eye cells called cones. Special nerves that respond to the visible light spectrum range send signals to the brain, which interprets them as light. No two people will see light exactly the same way, due to small differences in the retinas of their eyes. The ability to see light at different wavelengths also changes with age. In childhood, people usually can see at shorter wavelengths than when they are older.
- NASA Science: Wavelengths of Visible Light
- Florida State University: Molecular Expressions: Sources of Visible Light
- Eye (London, England): What Is Light? The Visible Spectrum and Beyond
- The University of Wisconsin-Madison: The Wonders of Physics: What is Light?
- Wired: 5 Things Every Human Should Know About Light