Diurnal Rhythm and the Role of Light Therapy

If you're very observant, you may have noticed that your energy levels, wake and sleep schedule, appetite, behavioural rhythm, and specific nudges follow the same pattern daily. 

These patterns may seem random, but they're not. They're part of or a consequence of your body's diurnal rhythm, a biological cycle that repeats every 24 hours.

However, these predictable patterns are vulnerable to external cues or signals, most notably the cycle of light and darkness. 

Consequently, disruptions to these external signals, such as irregular light exposure, inconsistent schedules, and poor lifestyle choices and diet, can throw off your internal clock and impact these daily patterns.

In this article, we'll explore diurnal rhythm meaning, how they differ from circadian rhythms, and the vital role that light plays in regulating these patterns. 

We'll also discuss how light therapy can help support a healthy rhythm, especially for those with limited exposure to natural sunlight or irregular schedules.

Diurnal rhythm and circadian pattern are similar, considering they both refer to events that cycle almost every 24 hours. 

An event classified as diurnal may or may not be classified as circadian. 

For a cyclic event to be classified as circadian, it  must continue  even in the absence of environmental/external timing cues or signals. That is, the circadian process is not generated in response to things like light and darkness. 

On the other hand, external timing signals like light and dark cycles trigger diurnal events. That's the significant difference between the two.

That said, environmental cues can still  help reset the circadian clock  to synchronise properly to the 24-hour cycle. However, the external cues do not trigger it as it's facilitated internally. 

Humans are diurnal, so understanding diurnal rhythm physiology is important. Diurnal means humans are most active during the day, even if there are some exceptions. Nocturnal animals are active during the night. 

Diurnal rhythms are the natural cycles our bodies follow every 24 hours. The autonomic nervous system  closely coordinates these patterns , helping regulate involuntary functions like heart rate, digestion, and body temperature based on the time of day.

Your diurnal rhythms determine when you feel alert or energetic. They also guide you when you feel hungry, sleepy, and other feelings. 

These patterns are the key to how our body works and responds to the environment.

We've established that diurnal patterns cycle every 24 hours. But how does the body and brain manage biological timekeeping and trigger events when due?

Although it's a bit more complicated than this, the simple answer is that your body runs on an internal timekeeping system, often called the circadian clock. 

This clock is in the hypothalamus  and maintains your body's daily schedule. Think of it as your personal assistant. 

Imagine using voice commands to trigger when your body releases certain hormones or activates essential body functions. There will be lapses and chaos. The central clock helps "automate" these biological processes.

In addition, every cell has its own mini clock, which takes cues from the circadian clock in the brain. 

When your internal biological clock  is perfectly synchronised to the 24-hour light-dark cycle, every diurnal pattern works as it should and happens predictably when it must. As such, you tend to wake up feeling refreshed, fall asleep at the right time, and your energy rises and falls in a predictable pattern.

The hypothalamus is the timekeeping HQ of the brain and body. The central clock is specifically  a cluster of cells  known as the suprachiasmatic nucleus (SCN). 

Does this clock remain precise for life without needing calibration or regulation? The answer is no. Your internal clock can go out of sync, leading to circadian misalignment.

The body uses light as a primary cue to stay aligned and synced with the 24-hour cycle. When natural light enters your eye, even while sleeping, special cells at the back of your retina send signals to the SCN. 

This initiates many physiological processes and molecular mechanisms, including lowering melatonin, brain activation, and cortisol release, to increase alertness and transition from a resting state to an active one. 

Hormones are chemical signals or messengers that the body releases to activate certain physiological processes. Research shows that several hormones have daily oscillations  dictated by the diurnal cycle. 

This means these hormones have been observed to have predictable peaks and lows within 24 hours. We'll examine some of these diurnal rhythm hormones below. 

Cortisol, secreted in the adrenal gland, is popular as a stress hormone, but it's much more. 

Cortisol rhythm is linked to the cortisol awakening response (CAR) observed when humans wake up. Between 30-45 minutes after waking up, cortisol level can increase by as much as 75%  of the level it was at awakening. 

Naps during the night do not elicit a similar cortisol response. 

Scientists suggest that "this activity, by mobilising energy reserves, prepares the body for the metabolic demands of the day.

Melatonin is the primary hormone responsible for regulating the sleep-wake cycle in humans. Melatonin production is influenced by the light-dark cycle.

The pineal gland begins to  secrete more melatonin one to three hours  before a person's typical bedtime, signalling to the body that it's time to begin winding down the day's business and prepare for sleep. 

That's why if you go to bed regularly at 9 pm, you'll begin to feel lethargic and sleepy before then, so that you fall asleep immediately after you get into bed. 

This secretion then  peaks in the middle of the night , between midnight and three in the morning, inducing maximum rest in diurnal beings. Disruptions in melatonin secretion can lead to rhythm sleep disorders, where you find it hard to fall asleep. 

Interestingly, melatonin also helps suppress cortisol production through a negative feedback loop.

As we've mentioned, light and darkness are the  most powerful signals or cues  the body uses to naturally keep your internal body clock in sync with the 24-hour day. 

So, when you expose yourself to sunlight every morning, you're practically hitting the reset button, signalling to your body that it's daytime.

It's particularly important to get that exposure as soon as possible, before 8, to maintain your natural rhythm. This will help reinforce wakefulness and lock in the start time for your body's active period. The goal is to give your brain a daily reminder of daybreak. 

You also  get vitamin D  from sunlight exposure, which is crucial for your mood and morale.

In the same vein, limiting bright lights from the early evening is essential to close out the cycle. 

Too little light during the day or exposure to bright screens and lights late into the evening can send mixed signals to your brain, thus disrupting your biological rhythms.

Going to bed and waking up at the same time daily is another crucial habit you can adopt for  maintaining a healthy diurnal rhythm . Chronic sleep restriction can disrupt your diurnal rhythm, leading to fatigue, mood swings, and impaired cognitive performance.

When your sleep and wake times are predictable, your body learns to anticipate these periods. So, when it's dark and your bedtime is near, your brain naturally begins to release more melatonin. 

Sticking to a consistent bedtime trains your body to release melatonin predictably  around the same time each night. This predictable rise in melatonin helps you feel naturally sleepy, making it easier to fall asleep.

Some tips to help you maintain a consistent sleep and wake schedule include:

• Set a specific bedtime and wake-up time, and stick to it, even on weekends or public holidays. You may occasionally deviate 30-45 minutes, but maintain that +/- range. 

• Create a bedtime routine, like reading a book or taking a shower, to signal your brain that it's time to sleep.

• Ditch your phone and all electronic devices at least one hour before bedtime.

• Make your sleep environment cosy, comfortable, and conducive for sound sleep.

Many of the hormones that regulate metabolism and appetite also operate diurnally. 

Researchers contend that " metabolic rhythms  are intertwined with nutrient availability," suggesting that eating well can help  fix the circadian rhythm  and make it in sync with the light-dark cycle. 

Also, having a consistent feeding/fasting schedule helps maintain your circadian or diurnal rhythms. 

The same applies to physical activity. Exercising at night, for example,  delays the circadian phase  and consequently delays sleep onset. Keep your activities limited to when the body is most active: During the day. 

If there's any takeaway from this section, it's that the diurnal " system anticipates and adapts  to daily environmental changes to optimise behaviour according to time of day." 

That anticipation is the key operative word here, highlighting the importance of activity timing. Adopt behaviours that align with your internal diurnal patterns. 

For example, food intake late at night and consuming high-fat and sugary meals or drinks is a no-no.

So, we've established that the body needs natural light to regulate the diurnal rhythm. 

But let's face it: there are so many reasons many people do not get enough sunlight daily, from work to lack of mobility, seasonal changes, and location. 

Light therapy is an alternative for such people to keep their internal clock in sync. It mimics the type of light emitted by the sun and has similar effects on your diurnal rhythm.

Ultimately, the effect on hormonal cycles is positive since bright light mimics natural light and regulates your diurnal rhythm. 

In one study, scientists exposed participants to bright light between 5 am and 8 am after exposure to dim light. 

The researchers found that the transition from low to bright light induced a significant reduction in melatonin levels and approximately a 50% increase in cortisol levels . 

This study highlights how bright light can alter how hormones behave throughout the day. 

The LuminetteAcross multiple publications, researchers agree that the optimal time for bright light therapy is  as soon as you're awake , preferably before 8 am. 

In terms of duration, the answer varies per bright light therapy device. The best practice is to refer to the product manual for instructions. 

The Luminette features three light settings, each with its recommended duration. A session could last up to 60 minutes on the lowest light settings.

As many as  10% to 38% of nonstandard or night shift workers  suffer from a condition where they feel extremely sleepy when awake and also struggle to sleep when they need it. 

Essentially, bright light therapy trains the body to stay awake and active during periods when it would normally do otherwise. 

The key is that bright light therapy suppresses the production of the sleep hormone melatonin, thus delaying when shift workers feel sleepy. Consistent use helps shift workers have better sleep patterns and be  more alert and active during their shifts . 

The same principles apply to  jet lag  and crossing multiple time zones, as the symptoms are mostly the same as those of  night shift work  disorder.

Luminette products have been proven, through third-party research studies, to be effective at:

A healthy diurnal rhythm is essential for numerous bodily functions to operate optimally. 

Your body relies on light cues to maintain your diurnal rhythm and ensure it's aligned with the Earth's light-dark cycle. 

Situations like shift work, remote work, artificial lighting, poor food choices, and more regularly throw your internal clock off course. 

The Luminette 3 wearable glasses or The Luminette Drive can help realign your diurnal rhythm alongside other solutions like a regular sleep schedule and sunlight exposure in the morning.