Chronobiology

Chronobiology and personalized light

Chronobiology is gaining importance in the understanding of human physiology. The innate rhythmicity of biological functions, where most fluctuate according to a circadian rhythm, thus prepare the body for daily recurring events such as eating and sleeping. The pancreatic clock regulates insulin secretion and its response to glucose; the hepatic clock regulates glucose clearance, the skeletal muscle clock regulates metabolism and glucose uptake, and so on³⁶. The suprachiasmatic nucleus in the hypothalamus is the synchronizer for all of the clocks in the body. It adjusts the production of hormones such as melatonin and cortisol. The timing of these processes is collectively called our circadian rhythm. Recent evidence points to a genetic variability of clock genes associated with individual differences in sleep and circadian physiology and non-visual response to light³⁷.

What is a circadian rhythm?

Circadian rhythms are the result of an adaptation to earth’s rotation applying a 24 hour structure on bodily physiology. Humans are genetically programmed to be diurnally active. The body with its physiology and metabolism organized around 24 hours is optimally functioning when this rhythm is paced daily by light. Light is the most important synchronizer for the circadian rhythms in the body. Many of the bodily functions, such as sleep, hormones and metabolism vary with the daily cycle given by day and night. The innate rhythmicity of biological functions, where most fluctuate according to a 24 hour circadian rhythm, prepare the body for daily recurring events such as eating and sleeping.

What is a chronotype?

It is evident that modern lifestyles vary significantly in relation to the natural light-dark cycle and influence our access to daylight. Eating habits, when, how and if we choose to exercise, travel schedules and work commitments all affect the bodily rhythms. These parameters are individual. People differ and so do their needs. The same light environment is registered by the circadian system very differently between individuals. People have different chronotypes that translates into their preferred timing of sleep and wake. Certain genes have been linked to morning-evening preference and genes that generate and regulate sleep and circadian rhythms are important for understanding the individual variances in sleeping behavior. The BioCentric Lighting™ system is easily customized according to the unique needs of the individual and the situation. The light environment provides adaptable light to fulfill the biological need for each day, regardless of season.

How does light affect us?

Most people have a circadian rhythm that is slightly longer than 24 hours

Light is the most important time cue for the circadian rhythm¹⁵. Light stimulates via melanopsin-containing ganglion cells through the retinohypothalamic pathway the suprachiasmatic nucleus (SCN)¹⁶. The SCN in the hypothalamus is the master clock in the human brain and controls the circadian rhythm¹⁷.
As in other mammals, in humans, the biological clock shows only a small variation between individuals. Most people have a circadian rhythm that is slightly longer than 24 hours¹² which means that it needs to be corrected daily in relation to the solar day¹³. Without correction, the circadian rhythm is shifted slightly every day and gradually falls out of phase compared to the 24-hour solar day¹³.

People with a circadian rhythm period above the average are people are commonly described as night owls and those with shorter period considered morning larks.

Night owls

Night owls are have a circadian rhythm period above the average. They tend to be more energetic in the evenings and can easily stay up later than average. They also have more difficulties waking up in the morning. Night owls would benefit from a light exposure that helps them wake up early in the morning to match their spontaneous wake up time with their work schedule. They would then also feel sleepy earlier in the evenings. 

Morning larks

Morning larks have a shorter circadian rhythm period. They easily wake up early in the morning – which may lead to insufficient sleep if they need to stay up late at night. The right light exposure would help these individuals keep their alertness level a little longer in the evening and get more quality sleep, up until the time they should wake up.

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It all starts in the eye.

Eye formation begins 22 days into embryonic development, and the eye constantly develops up to the age of 6-8 years. In the back of the eye we have the retina which consists of several layers. Outermost are the photoreceptors. Up until 2000 it was believed to only exist two types of photoreceptors, rods and cones. Recently a third photoreceptor with its own wavelength, separated from that of rods and cones, was discovered. Furthermore, this receptor was found in the ganglion cell layer and not in the photoreceptor layer of the retina. It contains melanopsin, a photopigment different from that of rods and cones with a spectra around 480 nm. The ganglion cells in the retina form the optic nerve that transport light information to the brain from the eye. Most of the nerve fibres projects to the visual cortex in the back of the brain. However approximately 5 % of the nerve fibres, those from the melanopsin containing ganglion cells, project directly on to hypothalamus and the suprachiasmatic nucleus where light information is used to synchronize the circadian rhythm with our surroundings.

LED & Light

Modern LED technology has introduced the possibility to adapt color saturation and brightness. Terms such as ”tunable white” and ”dynamic white” are often used within the lighting industry. The subsequent effect lighting has on health has led to the birth of a new term; Human Centric Lighting (HCL). However, to succeed in creating healthy lighting environments, both the LED technology and basic anatomy need to be considered. At BrainLit we use luminaries, sensors and control systems that adapt to real human needs instead of present standards. This is what we call BioCentric Lighting™. After years of extensive scientific research, we have produced innovative lighting environments that cater to individual needs.
Traditional lighting sources fail to regulate the circadian rhythm due to insufficient temperature, brightness or dynamic changes. It is estimated that 15-20 % of global electricity consumption is used with the purpose to generate lighting, from which less than 10 % of the energy ends up in useful light. This is caused by bad conversions or useless lighting, ”light pollution”. In addition, poor lighting environments with flickering and low intensity luminaires lead to high maintenance costs and negative health effects on humans and animals.
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Our LED technology is advanced in its endless possibilities for individual preferences and needs. The luminaires in our systems follow the natural daylight curve closely and mimics it both in intensity and color. Our lighting can be both static and dynamic depending on use and is always customizable. Whether you are looking for a scalable, fixed installation or are in need of something more flexible – try BioCentric Lighting™ and discover the difference.
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