Morning Sunlight and its relationship to sleep

Sunlight, especially morning sunlight, is often overlooked for health and wellbeing. Our circadian rhythms are closely linked to light exposure. In modern life, with artificial light and time indoors, our rhythms miss the natural light they need.

Circadian rhythm

Your circadian rhythm is your body’s 24-hour internal clock. It’s actually a bit longer than 24 hours. This rhythm helps decide when you feel awake or sleepy. Your suprachiasmatic nucleus (SCN) controls it. The second force is sleep pressure, known as adenosine. Adenosine builds up while you’re awake and is cleared during quality sleep. More adenosine makes you feel tired and sleepy.

Circadian rhythms are influenced by hormones, which change due to external factors like light. Your eyes have special cells that respond to light. They send signals about light exposure to the SCN. The SCN adjusts your rhythm based on two things: the time of day and the type of light detected.

The time of day is important. We are more sensitive to light in the hour after waking, two hours before bed, and during the night. The type of light also matters. Our bodies adapt to sunlight at different stages throughout the day.

Blue light

In the morning, after sunrise, we see white or blue light. This light comes from LED lights, fluorescent lights, and screens. In the afternoon, the light turns yellow and orange as the sun lowers in the sky or from orange light bulbs. In the evening, we have red light or darkness, seen from red light bulbs, candles, or fires.

The problem arises when we look at screens that emit strong blue or white light late into the evening. Phones, TVs, laptops, and tablets send this light into our eyes. This signals the SCN that it is still daytime, even when we are in bed trying to sleep. During the day, blue light helps us feel alert and boosts our performance and attention. However, blue light exposure in the evening suppresses melatonin. This hormone helps us feel drowsy and aligns with our circadian rhythm.

Fortunately, there are ways to reduce blue light exposure in the evenings without changing your routine much. Most devices have a night mode that limits blue light during certain hours. You can also add a blue light blocking screen protector to smartphones and tablets. Additionally, blue light blocking glasses are available for both daytime and evening use.

Morning Sunlight

Limiting evening blue light exposure is important, but morning sunlight is also beneficial for sleep. Morning sunlight suppresses melatonin and boosts cortisol levels. Although cortisol is often seen as a stress hormone, it helps improve alertness and focus, which are crucial for daily life. Problems arise when cortisol release is poorly timed. Low waking cortisol levels can lead to fatigue.

The cortisol-awakening response is how cortisol levels rise properly in the morning, peaking 30-45 minutes after you wake up. Morning sunlight can increase this peak by about 50%. This boost supports immune function, increases alertness, and helps set a sleep schedule for about 14-16 hours later. The rise in cortisol from morning sunlight acts as a hormetic stressor, making you more resilient to stress.

Along with improving alertness, morning sunlight enhances sleep duration, quality, and latency. It also lifts mood by increasing serotonin release, which later converts to melatonin.

Whoop, the wearable health and fitness tracker, have talked about this. They have a great article on morning behaviours that you can find here. Morning sunlight is one of the key habits that we include in our Sleep Mastery Journal, which you can find here.

Tools

Some tools you can use to limit blue light exposure late into the evening are:

Red light lightbulbs - designed to emit light at the red end of the visible spectrum (typically around 620-750 nanometers) while minimizing or eliminating the emission of blue and green light. The primary reason people use red light bulbs is to reduce their exposure to blue light, especially in the evening and before bedtime.

Blue light blocking glasses - designed with lenses that filter out a portion of blue light emitted from digital screens (computers, smartphones, tablets) and artificial lighting. The intention behind them is to reduce potential negative effects associated with blue light exposure.

Blue light blocking screen protectors - films that you can apply to your phone, tablet, or computer screens to filter out a significant portion of the blue light emitted. They are a passive way to reduce exposure without needing to adjust settings constantly.

Reduce overall screen time in the hours before bed - establish a "digital curfew": aim to power down all electronic devices (smartphones, tablets, laptops, TVs) at least 1-2 hours before you plan to sleep. This gives your brain a chance to wind down without the stimulating effects of blue light.