Many living organisms, from humans to plants and even bacteria, operate on an internal circadian rhythm — a roughly 24-hour cycle that regulates various physiological processes. This rhythm is primarily influenced by light exposure, known as the main time cue (or zeitgeber), but other factors such as feeding times and physical activity also play a role in synchronizing these internal clocks. The circadian system, in turn, modulates numerous bodily functions, including energy levels, body temperature and the secretion of hormones like cortisol and melatonin.
Circadian rhythm isn’t just about sleep patterns — it also impacts how awake and alert you feel in the morning and your energy and hunger levels throughout the day. Light exposure is one of the most powerful tools to shape your circadian rhythm, but the timing of light exposure can determine if it is beneficial or harmful to your circadian system and overall health. There are several types of phototherapy protocols used to treat medical conditions, and useful for overall health benefits ranging from treating psoriasis and acne, reducing inflammation and alleviating chronic pain (such as fibromyalgia).
Learn about Light Exposure and Circadian Rhythm
Circadian Rhythm Biology
Circadian rhythms are 24-hour cycles in our biology that regulate sleep, wakefulness and other bodily functions. When viewing light, melanopsin molecules inside the retina become activated, sending signals to the suprachiasmatic nucleus (SCN), located in the hypothalamus. The SCN, acting as the body’s master clock, receives light information from photoreceptors and orchestrates the circadian rhythm. Through complex neuroendocrine pathways, it indirectly influences processes like cortisol release via the hypothalamic-pituitary-adrenal (HPA) axis and melatonin production through the pineal gland.
Signals from the SCN communicate with virtually every cell in your body to coordinate the timing of various physiologic processes, which is why keeping your circadian rhythm consistent has such wide-ranging health effects. In fact, knowing the time is so important that each cell in your body has its own circadian clock regulated by genes such as the PER, BMAL and CLOCK genes.
Sunlight, Red Light and Blue Light for Health
Different types of light exposure significantly impact mental and physical health in unique ways. Natural sunlight is especially powerful: in addition to being magnitudes brighter than indoor light, retinal nerves can detect the time of day based on the ratio of blue to yellow light. Morning light exposure increases (healthy) cortisol levels, and exposure to outdoor sunlight throughout the day is linked to improvements in sleep quality, hormones and overall mood. Exposure to the afternoon sun helps adjust your eyes’ sensitivity and can buffer against the disruptive effects of artificial lights from screens and TVs in the evening.
On the other hand, increased exposure to artificial light — particularly at night — not only has negative effects on your sleep schedule but is also associated with increased symptoms of depression, anxiety and poor overall mental health.
Waking and Morning Protocols
How your mind and body feel during the first few hours after waking has a strong influence on the rest of your day. Following evidence-based waking and morning protocols can support energy, hormone and neurotransmitter levels that contribute to a focused, productive and subjectively more enjoyable (or at least pleasant) day.
To support your circadian rhythm, expose yourself to bright light soon after you wake up — preferably natural sunlight, or artificial light if it’s still dark outside. Morning physical activity may also help align your body’s natural rhythms. These practices can complement your body’s innate cortisol-awakening response (CAR), potentially enhancing overall circadian synchronization. Consider delaying caffeine intake for 90-120 minutes after waking as a strategy to support your body’s natural cortisol rhythm. While this approach may help optimize alertness for some individuals, keep in mind that responses to caffeine and its effects on cortisol can vary from person to person.
Everyone’s mornings look different, especially if you have children, work atypical hours or have other extenuating circumstances. These protocols are simply a guide towards better health; if you cannot implement these protocols perfectly, using them when you can is better than not at all.
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