Light surrounds us each day, but what exactly is it? A particle? A wave? Unfortunately, depending on the property being investigated, the answer varies from "one", "both", to "neither" as well as "we're not quite sure."
We sometimes define a "particle" of light as a photon, though unlike an actual particle, it does not have any mass. Or we may define the way light moves as a wave, but unlike other familiar waves – such as ocean or sound waves – light energy doesn’t have to travel through a physical medium like air or water… it can travel in the vacuum of space! This complex puzzle is still being unraveled, but what the scientific world does know can be explored in the Ocean Optics Web Book .
While we cannot precisely point to what exactly light is, we have gotten quite good at describing what light does. For example, whether we define light in terms of photons or waves, we know that it moves at very high speeds: 671,000,000 mph! In fact, it is impossible for anything to travel faster than light. See 10 Things Einstein Got Right to learn more!
We can also describe and categorize light. We do this based on its wavelength, which can also be expressed in terms of frequency. Wavelength is the distance between two crests (tops) or two troughs (bottoms) of the waves. Frequency is how many wavelengths pass a given point per second. Longer wavelength light has lower frequencies and less energy. Conversely, shorter wavelength light has higher frequencies and is more energetic. Now that we’ve addressed how wavelength and frequency are related, let’s explore different types of light with a focus on wavelength.
How is Light Categorized?
This spectrum of energy, or spectrum of light, is referred to as the Electromagnetic Spectrum. NASA explores the properties of different wavelength regions in the electromagnetic spectrum ranging from radiowaves to gamma rays. Right around the middle of the spectrum we have visible light - the rainbow of colors we know and love. Just shorter than visible light are the ultraviolet wavelengths, which we wear sunscreen to protect ourselves from. Just longer than visible light is infrared, which we sense as warmth on our skin.
Let's look closer at the visible light portion of the spectrum. Blue light is more energetic than red light; i.e., it has a shorter wavelength than red light. Specifically, we can say that blue light wavelengths are between 450-490 nanometers (nm) long whereas red light is 620-750 nm long. One nanometer is the equivalent of 0.000000001 meters. When discussing how light interacts with the ocean and atmosphere, we often refer to wavelengths in terms of nm.
PACE will measure light over a broader range of the electromagnetic spectrum and with more precision and detail than ever before. PACE's fine-resolution measurements, known as hyperspectral imaging, will provide new insights into our ocean and atmosphere. Want to learn more? Check out the Colorful World e-brochure.
How Does Light Move or "Behave"?
Most of the light reaching earth comes from our Sun. It is generated by nuclear reactions in the Sun's core that convert hydrogen into helium, releasing energy (photons!) in the process. For more information on how light is produced by the Sun, check out the Ocean Optics Textbook .
When there are no obstacles in its path, light travels in straight lines that extend in all directions from its source (like the surface of an expanding sphere/ball). Once light encounters an obstacle – say a molecule of carbon dioxide, the leaf of a plant, or an asphalt road – it will interact with that object in one of several ways. Check out the Sea the Light e-brochure for more information.