which light cannot be seen?

All electromagnetic radiation is light, but we can only see a small portion of this radiation—the portion we call visible light. Cone-shaped cells in our eyes act as receivers tuned to the wavelengths in this narrow band of the spectrum. Other portions of the spectrum have wavelengths too large or too small and energetic for the biological limitations of our perception.

As the full spectrum of visible light travels through a prism, the wavelengths separate into the colors of the rainbow because each color is a different wavelength. Violet has the shortest wavelength, at around 380 nanometers, and red has the longest wavelength, at around 700 nanometers.

The Sun is the dominant source for visible-light waves our eyes receive. The outer-most layer of the Sun's atmosphere, the corona, can be seen in visible light. But it is so faint it cannot not be seen except during a total solar eclipse because the bright photosphere overwhelms it. The photograph below was taken during a total eclipse of the Sun where the photosphere and chromosphere are almost completely blocked by the moon. The tapered patterns—coronal streamers—around the Sun are formed by the outward flow of plasma that is shaped by magnetic field lines extending millions of miles into space.

As objects grow hotter, they radiate energy dominated by shorter wavelengths, changing color before our eyes. A flame on a blow torch shifts from reddish to bluish in color as it is adjusted to burn hotter. In the same way, the color of stars tells scientists about their temperature.

Our Sun produces more yellow light than any other color because its surface temperature is 5,500°C. If the Sun's surface were cooler—say 3,000°C—it would look reddish, like the star Betelgeuse. If the Sun were hotter—say, 12,000°C—it would look blue, like the star Rigel.

Isaac Newton's experiment in 1665 showed that a prism bends visible light and that each color refracts at a slightly different angle depending on the wavelength of the color.

Close examination of the visible-light spectrum from our Sun and other stars reveals a pattern of dark lines—called absorption lines. These patterns can provide important scientific clues that reveal hidden properties of objects throughout the universe. Certain elements in the Sun's atmosphere absorb certain colors of light. These patterns of lines within spectra act like fingerprints for atoms and molecules. Looking at the Sun's spectrum, for example, the fingerprints for elements are clear to those knowledgeable about those patterns.

Patterns are also evident in a graph of an object's reflectance. Elements, molecules, and even cell structures have unique signatures of reflectance. A graph of an object's reflectance across a spectrum is called a spectral signature. Spectral signatures of different Earth features within the visible light spectrum ARE shown below.

Laser altimetry is an example of active remote sensing using visible light. NASA's Geoscience Laser Altimeter System (GLAS) instrument onboard the Ice, Cloud, and land Elevation Satellite (ICESat) enabled scientists to calculate the elevation of Earth's polar ice sheets using lasers and ancillary data. Changes in elevation over time help to estimate variations in the amount of water stored as ice on our planet. The image below shows elevation data over the West Antarctic Ice Streams.

Laser altimeters can also make unique measurements of the heights and characteristics of clouds, as well as the top and structure of the vegetation canopy of forests. They can also sense the distribution of aerosols from sources such as dust storms and forest fires.

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With review and contributions from Ophthalmologist Ernest Bhend, MD (Fort Mill)

Humans can see a wide variety of colors along the visible light spectrum. But the spectrum of light goes beyond red and violet, and these rays are invisible to the human eye. Today we’ll talk about infrared and ultraviolet rays, and why we can’t see them.

Before we talk about light we can’t see, let’s talk about what we can. The visible light spectrum is a section of the electromagnetic spectrum that the human eye can detect. The cones in our eyes act as receivers for radiation with wavelengths from 380 to 700 nanometers. This includes red, orange, yellow, green, blue, purple, and all the colors in between.

Infrared waves are a portion of the light spectrum that follows red. They have longer wavelengths than visible light, ranging from 700 nanometers to one millimeter. This renders them invisible to humans in almost all conditions. There are limited situations, though, when humans can see infrared light. If concentrated bursts hit the eye, they can be perceived as a flash of green light.

Infrared lights are commonly used in remote controls. They are also used in thermal imaging cameras or night vision goggles because infrared can be detected as heat. If you have ever seen the multicolored images from a thermal imaging camera, you are seeing these devices interpret infrared waves in a way that humans can see them.

Infrared light is often used in astronomy because it can perceive objects that would be too faint to detect in visible light.

While it is difficult for humans to see infrared light, some animals, like snakes and bedbugs, can detect it.

Ultraviolet light is a type of electromagnetic radiation that precedes the color violet in the light spectrum. The sun is the best-known source of ultraviolet rays.

Ultraviolet light has shorter wavelengths than visible light, with lengths of 10 to 400 nanometers. While invisible to humans, as with infrared light we can see the effects. For example, if you have ever watched a blacklight change the colors of a poster or seen a bank teller use one to detect counterfeit money, you are watching the effects of ultraviolet light. And, while you can’t see the rays themselves, ultraviolet rays are what cause people’s skin to tan in the sun.

Like infrared light, some animals can see ultraviolet rays. Bees, for example, can see this portion of the spectrum.

Even though you can’t see them, infrared and ultraviolet rays can still cause injury.

“Both infrared and ultraviolet light can damage the light receptors in the eye,” CEENTA Ophthalmologist Ernest Bhend, MD, said. “Be sure to wear proper eye protection to protect your eyes from this damage, especially good UV-blocking sunglasses if you are out in the bright sunlight.”

While infrared and ultraviolet light are invisible to the human eye, there are still plenty of things people can see. Don’t hesitate to visit a CEENTA eye doctor to make sure you can view all of them as well as possible.

Our eyes are sensitive to a narrow band of electromagnetic waves known as the visible light spectrum. To understand how visible light is broken into various wavelengths, take a cue from Isaac Newton and shine a light through a prism. A prism separates visible white light into separate wavelengths, and each color that appears—red, orange, yellow, green, blue, and violet—is a characteristic of the distinct wavelengths.

Certain colors are seen as objects around us and absorb some light and reflect the rest, depending on the properties of the object. For example, a strawberry reflects the wavelength of visible light that appears as red.

What about white and black? White is the result of a mixture of two or more colors of light. This is why visible light—or the mix of the rainbow of colors—is also referred to as white light. Black is the absence of the visible light spectrum wavelengths. Everything in a dark room appears black because there is no visible light to strike your eye as you gaze at the surrounding objects.

Blue light, or blue-violet light, has shorter wavelengths and more energy than any other visible light. While blue light helps regulate circadian rhythm and boost memory and cognitive function, excessive exposure can lead to digital eye strain, retina damage, and age-related macular degeneration. Special lenses like Eyezen™ can help with digital eye strain. For proactive blue light protection, Crizal® Prevencia™ anti-glare lenses can be a great solution.

A comprehensive eye exam with an eyecare professional can help you find the right lenses.

The human eye can only see visible light, but light comes in many other "colors"—radio, infrared, ultraviolet, X-ray, and gamma-ray—that are invisible to the naked eye.

On one end of the spectrum there is infrared light, which, while too red for humans to see, is all around us and even emitted from our bodies. Warm-blooded animals, including humans, radiate infrared light. That's why infrared cameras are helpful for thermal imaging and night vision when searching for people or animals.

On the other end of the spectrum there is X-ray light, which is too blue for humans to see. X-rays are another common light source that many of us have encountered at a doctor's office. X-rays can penetrate skin and muscles, allowing doctors to look at our bones. What you might not know is that the sun also emits X-rays. Lucky for us, the Earth's atmosphere blocks X-ray light.

Non-visible light can also be found in your home in a device you most likely use every day: remote controls! Your remote control uses infrared light to transmit signals to the television and other electronics. While the signal is invisible to you, your television can process the light and respond.

The light we can see, made up of the individual colors of the rainbow, represents only a very small portion of the electromagnetic spectrum. Other types of light include radio waves, microwaves, infrared radiation, ultraviolet rays, X-rays and gamma rays — all of which are imperceptible to human eyes.