Morning Light and Wakefulness
When we wake up in the morning, our adrenal glands secrete cortisol and a small amount of adrenaline in response to the activation of light signals, which initiates the state of wakefulness. At the same time, a 12-14-hour biological clock starts counting down until the release of melatonin from another gland in the brain, the pineal gland, which makes us feel sleepy and ready to rest.
The Dual Nature of Light Signals
However, everything has a dual nature, including the human body, which does not always want to receive light signals. To ensure the perfect operation of our circadian rhythm, especially in the morning when we wake up, our nervous system needs to receive as many light signals as possible to activate various biological activities more quickly and efficiently. But in the evening, everything changes. We need to minimize and avoid all light sources including sunlight, artificial lighting, and screens such as phones and computers.
Negative Effects of Light at Night
There are two reasons for this.
Light and Pineal Gland Function
First, light suppresses the normal function of the pineal gland. Why do we feel sleepy at night? After being awake for more than ten hours, our pineal gland starts to secrete melatonin, a hormone responsible for making us feel tired and sleepy, similar to a preprogrammed code. The pineal gland works best in a dark environment.
Any light, whether it is sunlight, bedroom lighting, or the light from phone screens, can inhibit the function of the pineal gland, which means it also inhibits the secretion of melatonin. In other words, these additional light signals that should not appear at this time make our brain think it is still daytime. As a result, the efficiency of the pineal gland decreases significantly, leading to insufficient secretion of melatonin, making it difficult for us to fall asleep or even causing insomnia.
This is a common mistake people would make when unable to sleep, continue to use their phones hoping to get tired and fall asleep. However, the light emitted by the phone screen actually further inhibits the effective secretion of melatonin, delaying the rhythm of successful sleep.
Light and Emotional Health
The second reason we need to avoid lighting at night is that late at night, roughly from 11 pm to 4 am, any light signals that enter our nervous system will activate a region in the brain called the Habenula or Disappointment nucleus, which can be understood as the emotional center of the human body. After this emotional center is activated, it inhibits the secretion and communication of dopamine, a neurotransmitter associated with positive traits such as happiness, well-being, energy, and motivation.
However, when we are in the evening, especially at midnight, our dopamine levels may already be naturally decreasing. When we receive excessive light signals from the environment, including dopamine and other emotion-related neurotransmitters, their communication is further inhibited, which can easily lead to negative emotions such as disappointment, anxiety, and depression. Even worse, these negative emotional states can spread and extend to the daytime, affecting our mood for the entire day. Therefore, once again, for the sake of our physical and mental health, especially our psychological well-being, we need to minimize all light sources at night, especially after 11 pm, including screens from phones and computers.
The Importance of Sunrise and Sunset for Our Circadian Rhythm
Weak Morning Light and Sensitivity Changes
It is important to note that the light emitted from phone screens in the morning is too weak to activate neural activity. However, why do we need to pay extra attention at night? Our visual nerve cells, which are the light receptors in our body, become more sensitive over time. When we wake up in the morning, they are very sluggish in sensing light, and the energy emitted by the phone screen is weak. Therefore, we need to include the powerful energy from the sun, especially during sunrise. If we receive 2-10 minutes of light signals from the sunset at low altitudes close to dusk, it will help delay the sensitivity changes of our visual nerve cells. This will make these light receptors less sensitive to light at night, thereby reducing the negative effects caused by excessive light signals. Of course, this only weakens these effects, and they do not disappear completely.
The Role of Sunrise and Sunset in Cultivating Healthy Rhythms
The key issue lies in the importance of sunrise and sunset in cultivating a healthy circadian rhythm. It is essential to let our body know when the day begins and ends because our body does not think like our brain does, knowing roughly what time is the end of a day. Our body needs external signals to know the start and end of a day, the cycle of day and night. These external signals are the sunrise and sunset, which serve as “anchors” for our body’s biological activities controlled by the nervous system. They provide a rhythmic reference for the secretion of hormones, metabolism, and a stable physiological and emotional state, making us more energetic and focused during the day and allowing us to fall asleep quickly and efficiently at night, recovering our energy for the next day’s activities.
Light signals play a crucial role in regulating our circadian rhythm, affecting not only our sleep but also our emotional well-being. To live a better life, we can make choices to optimize our exposure to natural light during the day and minimize artificial lighting at night. Embracing the natural cycle of sunrise and sunset can help us maintain a healthy circadian rhythm and ensure that we are energetic and focused during the day, while also allowing us to sleep well at night. By working in harmony with our body’s natural rhythms, we can support our overall physical and mental health.
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