Sunlight and health

You have probably heard about sunlight helping your body make Vitamin D, but there is also new research coming out on the benefits of sunlight for heart and blood vessel health. There are also new findings that improve what we know about sunlight exposure and skin health. What exactly about sunlight exposure would affect our blood vessels? Can spending time out in the sun improve your mood? Before we get into how sunlight affects our health, let’s dig in to explore what sunlight is exactly.

A star is born

About 4.6 billion years ago the sun was formed. This marks the beginning of life as we know it, and we can thank the sun for keeping us warm and providing energy to the solar system we inhabit. Our best guess is the sun will remain stable for about another ~5 billion years.

The light spectrum

Light is electromagnetic radiation that travels at different wavelengths. The particles that carry this electromagnetic energy are called photons*. The sun emits 10% ultraviolet (UV) light, 40% visible light, and 50% infrared light. This is visualized below.


You can see the length of each energy wave increases from left to right, conversely the energy of photons decreases form left to right. In other words, wavelength and the energy of each photon (energy wave) are inversely related. Let’s talk about UV light, visible light (the kind we can see), and infrared light.

Ultraviolet light

As for UV light, there are three main types (listed from longest to shortest wavelength): UV-A, UV-B, and UV-C. Long-wave UV-A is not absorbed by the ozone layer, thus photons in this range can reach our body. Medium-wave UV-B is mostly absorbed by the ozone layer, but some of it reaches us. Short-wave UV-C is completely absorbed by earth’s ozone layer (Which is a good thing as this is the most dangerous type). This means most our body is influenced mostly by UV-A and to a lesser extent by UV-B.

Visible Light

The photons within the visible light spectrum cause a conformation change (change in the shape of a form of vitamin A within our eye) in our retina, which allows us to see. The varying amount of energy input from these photons helps us identify colors within the visible light spectrum. Pink Floyd fans may be picturing how light is dispersed through a triangular prism right now.

Our retina can sense visible light at wavelengths from 390 to 700 nanometers (nm). Black lights (a term used interchangeably with the black light blue lights we are likely familiar with “seeing”) emit radiation at wavelengths ranging from 307-420nm. Because of the overlap in wavelength ranges (390-420nm) we can see the violet shades of light emitted from blacklights, but not the UV-A light (307-390nm).

What about things that glow in the dark? Generally, these items are fluorescent. Some materials that store energy for later photoluminescence (or glowing) use phosphorescence, which is essentially energy that is stored and later released as radiation in the visible light spectrum.

Infrared Light

Photons from the infrared spectrum provide heat energy, we feel this from a distance of 93 million miles away. But, you may have stepped into an infrared light box at some point in your life if you have visited a sauna (though not all saunas use this to stay hot). Also, near-infrared light can be helpful for seeing in the dark, you just need to grab a pair of night vision goggles.

What is coming up next?

We are at the tip of the iceberg for sunlight and how it affects our bodies. Now that we know the different components of sunlight, we can begin to explore how each plays a role in different parts of our health. Moving forward, we will learn about how sunlight affects our heart, blood vessel, and skin health, how sunlight affects our sleep-wake rhythm, and more.

Until next time, feel free to share your thoughts, comments, and questions.

Thanks for reading.

This piece was edited by Austin Robinson, PhD.
Shout-out to Andrew Kuczmarski (Scientist and Photographer) for providing the cover photo for this post.

Curious to learn more? Check out these related resources.

*paradoxically, energy carrying photons have no mass

A two-minute and 11-minute video about sunlight

Article: How the sun was formed

“Spectrum of Light” photo attribution