What Is Light?
Light might seem like a simple concept. We wake up every morning, and sooner or later the Sun rises and things get "light." Or, we walk into a dark house and flick a switch and where there was once darkness, there is now light.
But what exactly is light?
Despite being 93 million miles from the Earth, the Sun delivers approximately 5 trillion giga-joules of energy to the Earth's surface every year. Credit: NASA/JSC
Light is so much more than the “either/or” of illumination. Our human eyes can see only a certain narrow range of light. We also know that light actually encompasses everything from radio waves to infrared light to X-rays and gamma rays. What we call light is only the small fraction of visible light that our eyes are sensitive to. It’s also exactly the slice that our Sun radiates most strongly. In other words, our default definition of light comes from the fact that we evolved on this particular planet around this particular middle-aged, medium-temperature star the Earth orbits around.
Light can take the form of radio waves, microwaves, infrared, ultraviolet, X-rays and gamma rays, which are collectively known as the electromagnetic spectrum. Credit: NASA/CXC/M.Weiss
Our daily perception of light is akin to listening to only the oboe section of the symphony. If we ignore the rest of the instruments, we miss out on the harmony of the whole composition.
Technology and advances in scientific understanding have enabled us as humans to overcome our oboe-tuned senses. Today, we have access to a treasure trove of information about light that would otherwise be undetectable to us. This exploration has opened up entirely new worlds – both figuratively and literally – on our planet and across the cosmos. It is no exaggeration to say that light is the very way we learn about the Universe in which we live.
Our Sun shines in many different kinds of light. What we see from the bright yellow orb in the sky each day is just a very small portion of the light our very own star radiates. This image of the Sun shows us how it looks in extreme ultraviolet light, which is much hotter than visible light. You can see about a dozen active regions captured from May 14-18, 2015. Credit: NASA/Solar Dynamics Observatory
While light is critical to our exploration of our surroundings, it has taken humankind a long time to understand it. It has taken the hard work of scientists, philosophers, and inventors spanning from ancient Greece to modern times to begin to piece together how light actually works and why it behaves as it does.
Our forthcoming book “Light: The Visible Spectrum and Beyond” will reveal some of the secrets that have been uncovered, what we know about light today, and how we can harness it for our benefit here on Earth. We’ll be diving into some of these bits here on our blog as well. We hope it might shine a light on just how extraordinary this utterly ordinary phenomenon is.