Light for Life: What is the Limit? By Dr. Jyoti Keswani

Light is a form of electromagnetic radiation. It travels both as light waves and as a stream of particles called photons. This form of radiation is essential for life. It drives photosynthesis in green plants. This process provides food and produces oxygen necessary for the survival of all living beings. Humans see only a portion of the total light spectrum. This portion forms the basis of vision perception, enhancing life’s beauty. Light powers modern technology. For example, light from the Sun is a source of clean energy. Solar panels harness this energy. It is crucial for the operation of many technologies. Fiber optic cables rely on light to function. It plays a significant role in various ecosystems. It guides animal behaviour from their daily activities to their mating and migration. It keeps the planet warm and creates the energy necessary for survival.

However, light has more role to play than mentioned above. Apart from enabling us to see the world, it distinguishes colours, shapes, and movement. Light also serves functions such as initiating and regulating metabolic processes. It influences circadian sleep-wake cycles, moods, and energy levels. Natural light helps regulate the body’s internal clock, impacting mood, energy levels, and overall well-being. Sunlight helps in the production of Vitamin D, which is vital for maintaining strong bones and a healthy immune system. Thus, light is crucial for physical and mental well-being.

Light, Pineal Gland and Supra-Chiasmatic Nucleus (SCN):

Decades of research on mode of entry of light and its influence on physiological functions through Circadian rhythm or Sleep-Wake Cycle has led the scientists to new conclusions. They believe that rods and cones have little role in photosensitivity. It is now believed that certain photo-pigments are sensitive to blue light. These include non-rod & non-cone mediated vitamin B-based Cryptochrome and vitamin A-based Melanopsin present in the inner retina in the eye. Photoreceptors apply this light information by the process of entrainment of light from the external environment. This process resets and adjusts the biological clocks.

Suprachiasmatic Nucleus (SCN) is a paired structure with two parts. One part is the ventral core, Present above the Optic Chiasma. The other is the Dorsal Shell. The projections from SCN also reach hypothalamus, Possibly playing a role in the arousal Function of the Circadian Timing System. Light information received by the photoreceptors is now proven to be Transduced. This transduction happens to the ventral core of SCN through the Retinohypothalamic tract. SCN uses the light information to control the pineal gland. It does this through a multi-synaptic pathway. This process controls the circadian rhythm.    

The pineal gland also has photosensitive qualities. It uses external light to generate an entrainment of the body to daily (circadian) rhythms. It also adjusts the body to seasonal (circannual) rhythms of the sleep–wake cycle. The Pineal gland lacks a blood–brain barrier. Therefore, it permits a direct reception of exogenous substances. It also allows endogenous hormones or neurotransmitters to enter via the peripheral circulation. In addition, Melatonin is a main hormone produced by it. Melatonin is highly lipophilic. This property makes it easily transferable across cell membranes of epithelial cells. It moves easily through the blood vessels, lymph vessels, serous cavities, and the cavities of the heart. Melatonin levels in the body can be assessed through blood and saliva. It can also be evaluated through cerebral spinal fluid (CSF) and male seminal fluid. Amniotic fluid and intraocular fluids are also used for this assessment. These characteristics make the Pineal gland a master gland. They Enable it to act as the primary endocrine transducer. The Pineal gland also acts as the regulator of hormonal signals.

Optimum Light Requirements:

Living organisms need light to complete various processes. However, there are certain species that thrive in darkness. The requirement of duration and intensity of light for this varies from species to species. For example; plants require 12-18 hours of light per day for photosynthesis whereas humans require 12-12 hours of light-dark cycle. The colour of light is also important with blue light from natural and artificial sources being the most significant from point of view of its influence on both photosynthesis in plants and circadian rhythm in humans. Researches have proven that while insufficient exposure to light may be detrimental for growth and normal functioning, excessive light can also be damaging. In plants, excessive light intensity results in photodamage and photoinhibition, which are forms of stress. In humans, a number of physiological and psychological disorders have been reported, including poor sleep quality, mood disorders, cognitive dysfunctions and social jetlag.

Intake of Excessive light:        

Blue light is a portion of the visible light spectrum that can influence alertness, hormone production, and sleep cycles. This wavelength of light is emitted by LED and fluorescent lights, as well as many electronic devices especially television, mobiles, tablets and computers. With the advent of artificial light and electronics, people are being exposed to increased amounts of light before bedtime. Light from electronic screens comes in all colours, but the blues are the worst because it mimics the daylight and gives a notion of being in daytime even if it night. This leads to suppression of Melatonin from the pineal gland. Normally, its secretion starts in the evening hours, reaching a peak at midnight after which it starts declining. This surge is to prepare the body for sleep promoting rest and repair. Darkness helps to trigger the release of melatonin hormone but blue light delays it. Screen light, which is considered a blue light, can desynchronize the body’s internal clock or circadian rhythm leading to delayed sleep onset, reduced REM sleep which is vital for cognitive functions and overall well-being, increased alertness, difficulty to relax and to fall asleep. It also elevates our body temperature and heart rate. During the day, exposure to blue light can improve performance and attention, tuning our circadian rhythms and preparing for a good quality night sleep after the sun sets. According to American Optometric Association (AOA), more than two hours of screen time leads to Computer Vision Syndrome.

Screen Addiction:

It has been observed that teenage students are more sensitive to the effects of blue light than adults. They are more prone for addiction to the screen or Problematic Internet Use (PIU) also. The addictive effects of the light on the brain are more of behavioural nature than the chemical one. It has been attributed to Dopamine Reward System in the brain. Screen Addiction is the term given to compulsive and uninhibited urge of using electronic devices. It is seen as online shopping addiction, online gaming or gambling addiction etc. In long run, any type of screen addiction leads to harmful effects on all dimensions of health.

Health Hazards of Screen Time:

The physical harms include eye strain, dryness of eyes, blurred & double vision, sleep disturbances, neck pain, shoulder pain, Carpel Tunnel syndrome, headaches and persistent fatigue. Using screen for long time comes with physical inactivity leading to weight gain and musculoskeletal issues. The mental effects include ring anxiety, irritability, emotional volatility etc. It also can cause social isolation as it has led to people living in a virtual world, loneliness, non-involvement in recreational & relaxing activities. In students, screen addiction often culminates in poor academic performance due to reduced attention span and creativity. Cyber bullying is another menace faced by students whose life is governed by likes & dislikes. When restricted, screen addiction manifests certain withdrawal symptoms such as restlessness, anxiety and depression due to dopamine decline.

How to limit Light?

Researches have shown an increase in the usage of electronic devices leading to intake of blue light within an hour of going to bed which can lead to above mentioned health hazards. Following lifestyle modifications can be adopted in order to use screen productively with minimum hazards:

• The first practice to adopt in daily life is to adopt a strategically timed exposure to blue light.  This involves decreasing exposure to blue or screen light right from the evening by not using screens for an hour or two before bedtime. This is an important way to help the body’s Melatonin System to get adapted to less light and naturally prepare for sleep thus getting quality rest. Some people try to solve this by dimming their screens or wearing special glasses but there is no evidence of their efficacy.
• Use of night mode or blue-light filtering apps and using dim, red-tinted lighting in the evening is another alternative which has as the least impact on circadian rhythm has been advised.
• The bedroom should be completely dark in the night; if that is not possible, a sleep mask can be used to minimize light exposure. 
• Maintaining a regular sleep schedule is very crucial as this also helps to regulate body’s internal clock and improve sleep quality. 
• Use of 20-20-20 rule advocated by AOA can also help in which the person has to take a 20 second break after 20 minute of screen use to focus on an object at least 20 feet away. This helps to relieve temporary eye strain.
• Digital Detox is a popular practice among people with severe screen addiction which encourages the person to ration the personal or non-occupation related screen time.  
• Lifestyle changes like finding more productive hobbies and recreational methods can help. This includes spending time with family & friends, cooking, gardening, evening walks, listening to soothing music on radio or speakers (not screen) etc.
• Mental health interventions like individual counselling, Cognitive Behavioural Therapies, Meditation, Music Therapy can help.

Conclusion:

It is true that without light, the world would be a place full of darkness and despair. Light controls all the fundamental processes on Earth from photosynthesis and respiration to regulating our day and night routines. It powers the modern lives and maintains the comfortable lifestyle. Thus, light has become an indispensable element. However, its imprudent applications have caused certain harms which are reversible. Mindful and prudent use of light is therefore being advised to minimize the harms and maintain it as a boon forever.

Book Published By Author

Also Read: The Connection Between Circadian Rhythm and Gut Health

References:

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