Light Explained: Light, Energy and Radiation

Light is like air, it is all around us but we don’t think about until we need it. To understand light, you need to first understand Energy and Radiation.

Spectrum of the Sun: image credit NASA’s Goddard Space Flight Center Scientific Visualization Studio


Light Begins with Energy
Light is a form of Energy; so therefore we need to start with an explanation of energy before we can discuss light. Energy is a measurement; in the same way we define height, width or weight as a property of an object, so too is energy a property of an object.

Energy is a measure of an object’s ability to do work. Energy is non-tangible, we don’t see energy but we see its effects. You can’t see gravity but you can easily view it in action by dropping something on your foot.

There are many different types of energy – electrical, chemical, thermal, nuclear and magnetic to name a few. Light belongs to a type of energy called Electromagnetic Radiation.


Are You Telling Me Light is Radioactive?
Radiation can be a scary word that conjures up images of atomic explosions and mutations. But radiation is just the scientific term for energy that is moving through space. When we turn on a light bulb we are actually creating low-energy light radiation. The light waves that are emitted from our bulb are not harmful to living things, but we still consider them radiation.

Slices of the sun viewed in different wavelengths
The different wavelengths of electromagnetic radiation emitted by the sun. NASA’s Solar Dynamics Observatory (SDO) can capture these wavelengths and convert them into an image that our eyes can see. (Credit: NASA Goddard Space Flight Center)

Visible light is a member of the Electromagnetic Radiation family (or Electromagnetic Radiation Spectrum). Other members of the spectrum include radio waves, microwaves, infrared, ultraviolet, x-rays and gamma rays. These are all different frequencies of electromagnetic radiation, just like your favorite radio station is one frequency on your FM dial.

Our eyes can only pick up a tiny section of frequencies on the spectrum. The light our eyes can detect is called Visible Light. The other frequencies of electromagnetic radiation that are invisible to our eyes need to be observed with other man-made detectors like X-Ray machines and radio telescopes.

Did you know that some animals can see just outside the visible light spectrum? They can detect infrared and ultraviolet radiation to allow them to move easily at night or to let them see markings on objects and creatures that are invisible to us.


Our Eyes See Just One View of the Cosmos
When we look up at the skies or peer through a telescope, our eyes can only see the visible light of planets, stars and galaxies. However all of these objects emit energy across the electromagnetic radiation spectrum. So we have built specialized telescopes both on land and in space that can observe space in these other frequencies.

Humans see a small part of the Electromagnetic Spectrum
Humans can only detect a tiny portion of the electromagnetic radiation spectrum; we call this Visible Light. (Credit: NASA Mission Science )

We use Ultraviolet and X-Ray telescopes to study stars and galaxies, Gamma Ray telescopes to study supernovas, pulsars and black holes, Radio telescopes to listen to noises from space, Infrared telescopes to study cooler objects in space like brown dwarf stars, and Microwave telescopes to uncover the age and nature of the Universe.

Volumes of books have been written on the many forms of energy and how they effect the physical world around us. But if you can remember the following few points, you will have a good foundation for learning the role of light in astronomy.

  • An object such as a star constantly emits Energy
  • Radiation is a name for energy traveling through space
  • Some of this radiation is Electromagnetic Radiation
  • Our eyes can only detect small section of electromagnetic radiation called Visible Light
  • Other man-made devices can detect the other electromagnetic radiation frequencies


In our second article about light, we discuss how long it lake energy (and therefore light) to travel from a point in space down to our eyes on Earth.

Read Light Explained – Part 2: The Speed of Light

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