When people think about improving their health the first thing that comes to mind is probably some combination of eating better, exercising more, and using recreational substances less. Almost nobody would think about fixing their light environment as a primary lever for improving their health. Yet, your body uses light as a primary input for regulating a number of physiological processes including certain hormones, energy production, cellular repair, neurotransmitter balance and more. Light is one of those foundational health pieces that gets largely ignored by conventional advice. Getting your light environment right doesn’t require any expensive biohacking tools or supplements. It requires understanding what your biology actually needs to function optimally, and making a few deliberate choices each day.
The Evolutionary Picture
Before getting into the biochemistry, its worth noting the light environment with which we evolved to contextualize this science. Our ancestors evolved primarily on the plains of Africa. Each morning they’d wake up to the sunrise, each evening they’d go to sleep once the sun had set. Much of the day was spent in full-spectrum sunlight, with the only break from this was the shade of nearby trees. There was no real concept of indoors, just the natural light environment that was present. This is the environment that formed the very basis for our existence, and it should be no surprise that our biology responds to light in very specific and important ways. The modern environment represents a dramatic shift of this evolutionary baseline, and the consequences are substantial.
Light and the Circadian Rhythm
Your circadian rhythm is your internal 24-hour clock. It governs sleep and wakefulness regulating levels of melatonin and cortisol, as well as regulating immune function, body temperature and cellular repair. This master clock lives in a small region of the brain called the suprachiasmatic nucleus (SCN) and is primarily set by light.
In the morning, blue and UVA rich sunlight hit your retina and signals to the SCN to trigger a cortisol spike. This is your body’s natural alarm system. It initiates wakefulness, fuels mental clarity, and sets the timing for all downstream hormonal events throughout the day. In the evening, as light fades, the pineal gland begins secreting melatonin, the hormone that initiates sleep and orchestrates overnight cellular repair.
Modern artificial light disrupts the natural signals with which we have evolved. The blue light emitting screens, and bright LED overhead lighting both send your body early and midday alertness signals, even if it is actually close to bedtime. Evening blue light has been shown to delay melatonin secretion, compressing your sleep window, reducing overnight cellular repair, and desynchronizing the downstream hormonal cascades that your body depends on.[1]
Researcher Satchin Panda found that each of your cells and organs runs its own circadian clock. His lab showed that thousands of genes across every major organ system switch on and off at specific times of day, coordinating when to perform certain tasks and when to initiate repair.[2] The master clock in the SCN sets the schedule via light signalling, and when that signal is disrupted the downstream consequences ripple through your entire body.
Light and Mitochondrial Health
Your mitochondria don’t just run on the food you eat. They are uniquely sensitive to your light environment, and certain wavelengths have significant effects on their function.
Red and near-infrared light directly stimulate mitochondrial activity by interacting with cytochrome c oxidase, a key enzyme involved in the electron transport chain, the process by which your body creates energy. Getting sufficient amounts of these wavelengths stimulates ATP production, giving your body the energy it needs to perform all its daily requirements and leave you feeling your best.[3] These wavelengths are found outside and penetrate cloud cover. This is why its important to get outside for a significant amount of time each day.
UV Light exposure also directly speeds up mitochondrial function. These are available from direct sunlight on your skin, and is one reason why many feel so much better after a day basking in the sun.
Blue Light exposure has been shown to generate reactive oxygen species in the retina and other tissues, producing oxidative stress that impairs mitochondrial function.[4] Blue light also acutely stimulates dopamine release, which is partly why screens feel rewarding and are hard to put down. However, chronic over exposure appears to deplete dopaminergic neurons over time, facilitating addictive and instant-gratification seeking behaviours.[5] Obviously we have been exposed to some amount of natural blue light during our evolution, but our modern environment represents a significantly increased level of exposure from that with which we evolved.
Light and the Immune System
UVB radiation triggers Vitamin D synthesis in your skin. Vitamin D is not just simply one molecule, but rather a hormonal signalling system that regulates hundreds of genes, governs immune function and has well-documented anti-cancer properties. It’s worth noting explicitly that the benefits of sunlight induced Vitamin D synthesis go beyond anything a pill can replicate. When UVB hits your skin, it triggers a cascade of related photoproducts with their own biological effects, including compounds that demonstrate anti-cancer activity in skin cells.[6] The simultaneous release of nitric-oxide, beta-endorphins, serotonin, and these photoproducts that accompany Vitamin D synthesis in real sunlight provides a whole signal with unique benefit that an isolated supplement is unlikely to sufficiently capture.
Its worth noting that most conventional sunscreens block UVB, the very wavelength responsible for many of these benefits. Consider getting some daily sun exposure on your skin before reaching for sunscreen, or during lower UV hours if you burn easily. I’ll make a separate post about sunscreen and the fear-mongering surrounding sunlight but for now I will just emphasize the health benefits of these wavelengths with which we’ve evolved.
Light and the Cardiovascular System
UV light on the skin stimulates the release of nitric oxide. This in turn causes dilation of the blood vessels, lowering blood pressure and improving blood flow throughout the body.[7] The main source here once again is direct sunlight on the skin. Infrared and near-infrared radiation has been shown to build structured water inside and around cells. This is an emerging area of research but has implications for endothelial function that scientists are continuing to investigate.[8] Near-infrared light is most available close to sunrise and close to sunset, while the sun is lowest in the sky, where true infrared light is really only available through a dedicated infrared sauna.
Summary of Different Light Spectra and Health Effects
| Wavelength | Function | Availability |
| Blue Light | Signals wakefulness Suppresses melatonin and stimulates cortisol Impairs mitochondrial function in excess Stimulates dopamine but depletes dopaminergic neurons in excess over time |
Natural morning light Artificial light and screens Absorbed through eyes |
| Red and Near-Infrared Light | Increased mitochondrial function via cytochrome c oxidase Builds structured water |
Available during the entire day but highest just after sunrise and just before sunset Penetrates cloud cover Absorbed primarily through skin (majority blocked by clothing) |
| UV Light | Speeds up mitochondrial function Essential for Vitamin D synthesis and hormonal cascade Blood Vessel Dilation |
Available during the day, primarily between mid-morning to mid-afternoon Sun must be high in the sky (not available much during winter at northern latitudes) Absorbed through skin (blocked by most clothing) Reduced by cloud cover (by up to 50%) |
Practical Takeaways
1. Get morning light within an hour of waking- Aim for 20-30 minutes of outdoor light exposure in the morning. This is the single most powerful input for setting your circadian clock. Even outdoor light on an overcast day still far exceeds the absolute level of brightness in indoor settings. Remember to leave the sunglasses alone here, as the circadian signal is primarily an ocular pathway and requires full spectrum light to work optimally. The morning also offers significant amounts of red and near-infrared light that stimulates mitochondria and builds structured water.
2. Take consistent light breaks throughout the day- Every phone call, gap between meetings, or moment you step away from your busy life is an opportunity to get outside for a few minutes. The cumulative effect of these brief exposures adds up meaningfully
3. Don’t be afraid to show some skin- Remember that many of these beneficial light spectra are absorbed through your skin. Try wearing some short-sleeved shirts, shorts, or even taking off your shirt when appropriate to get these beneficial wavelengths of light on your skin
4. Control your evening light environment- Switch off most overhead lights after sunset, and prioritize lamps as your primary light source. Warm, low, indirect light in the evening instead of bright overhead lights will help your melatonin system function properly.
5. Protect yourself from blue light- Consider getting an app like f.lux to shift your screen towards warmer tones, especially after sunset. On phones, use specific night display modes or change your display colours to a deep red setting in the evening. For situations where you can’t control your environment consider bringing a pair of blue blocking glasses.
References
- Chang, A.M., Aeschbach, D., Duffy, J.F., & Czeisler, C.A. (2015). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences, 112(4), 1232–1237. https://doi.org/10.1073/pnas.1418490112
- Panda, S. (2013). Circadian physiology of metabolism. Salk Institute for Biological Studies. Retrieved from https://www.salk.edu/scientist/satchidananda-panda/
- Hamblin, M.R. (2016). Shining light on the head: Photobiomodulation for brain disorders. BBA Clinical, 6, 113–124. https://doi.org/10.1038/srep30540
- Nakashima, Y., Ohta, S., & Wolf, A.M. (2017). Blue light-induced oxidative stress in live skin. Free Radical Biology and Medicine, 108, 300–310. https://doi.org/10.1016/j.freeradbiomed.2017.03.010
- Romeo, S., Viaggi, C., Di Camillo, D., Willis, A.W., Lozzi, L., Rocchi, C., Capannolo, M., Aloisi, G., Vaglini, F., Maccarone, R., Caleo, M., Missale, C., Racette, B.A., Corsini, G.U., & Maggio, R. (2013). Bright light exposure reduces TH-positive dopamine neurons: implications of light pollution in Parkinson’s disease epidemiology. Scientific Reports, 3, 1395. https://doi.org/10.1038/srep01395
- Holick, M.F. (2013). Sunlight and vitamin D: A global perspective for health. Dermato-Endocrinology, 5(1), 51–108. https://doi.org/10.4161/derm.24494
- Liu, D., Fernandez, B.O., Hamilton, A., Lang, N.N., Gallagher, J.M.C., Newby, D.E., Feelisch, M., & Weller, R.B. (2014). UVA irradiation of human skin vasodilates arterial vasculature and lowers blood pressure independently of nitric oxide synthase. Journal of Investigative Dermatology, 134(7), 1839–1846. https://doi.org/10.1038/jid.2014.27
- Pollack, G.H. (2013). The Fourth Phase of Water: Beyond Solid, Liquid, and Vapor. Ebner & Sons. University of Washington.