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. New findings also improve what we know about sunlight exposure and skin health. What exactly would sunlight exposure affect our blood vessels? Can spending time out in the sun improve your mood? Before we examine how sunlight affects our health, let’s dig in to explore what sunlight is precisely.
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), 40% visible, 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 from left to right. In other words, the 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. The ozone layer does not absorb long-wave UV-A. Thus, photons in this range can reach our bodies. The ozone layer mostly absorbs medium-wave UV-B, but some reaches us. Short-wave UV-C is completely absorbed by the earth’s ozone layer (Which is a good thing as this is the most dangerous type). This means most of 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.
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 307-420 nm. Because of the overlap in wavelength ranges (390-420 nm), we can see the violet shades of light emitted from blacklights, but not the UV-A light (307-390 nm).
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, energy 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 help you see in the dark; you 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 explore how each plays a role in different parts of our health. Moving forward, we will learn about how sunlight affects our heart, blood vessels, 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.
-Joe
Austin Robinson, PhD, edited this piece.
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
