The levels of light strongly influence the lives of animals and human beings alike. According to scientists who conducted experiments on animals to determine if they can sense the seasons in the absence of light, it was found that animals can perceive the coming of seasons without any light.

From this, the scientists concluded both animals and human beings possess an in-built biological clock that can keep approximate time and can work smoothly in the absence of an external stimulus such as sunlight.

This biological clock, however, is only approximate and best used in the short term-not more than 24-48 hours in pitch darkness. When we use our body clock in natural sunlight, it fine tunes our clock to make it synchronise with the environment outside. If we don’t reset our body clocks but continue to keep it the way it is, we end up with problems such as hormonal imbalances, sleep disorders, and mood disturbances.

Like animals, we too need to rely on solar signals to keep our body clocks precise and our activities synchronized; human beings too need sufficient daylight to synchronize their circadian and circannual rhythms.

Circadian rhythms refer to the 24-hour-period of light and dark and sleep and wakefulness to which our body functions are set. We are programmed to wake each day, become hungry, tired, and later energized.

Apart from this, there is a predictable pattern of activities that is started and overseen by being exposed to sunlight and darkness. This cycle involves the working of body temperature, heartbeat, blood pressure, hormone levels and urine flow rise and fall. On the other hand, the circannual rhythm comprises the annual cycle all human beings use.

The fact that we are faced with a series of illness that are due to hormonal imbalances such as lack of sleep, low appetite, mood swings and reproductive disorders are all linked to a break in circadian rhythms that are largely due to a lack of sufficient sunlight.

Seasonal Affective Disorder (SAD) is one such example where disturbed sleep patterns, lack of appetite, weight disorders and depression manifest themselves in an annual cycle. At the peak of winter, the symptoms reach their pinnacle and worsen at night. SAD patients do well with a burst of artificial daylight or light therapy to correct their problems, proving thereby that SAD is directly linked with insufficient light.

Other diseases caused due to a break in the circadian rhythm include classical depression that has a daily rhythm. This is at its worst in the morning and gradually improves through the day and in the evening. As a result, the symptoms experienced are mood swings, insomnia or disturbed sleep patterns.

Today, while classical depression is being treated with drugs that exert a positive influence on the circadian rhythms, light therapy is also being used successfully. Irregular menstrual cycles or premenstrual syndrome are two more examples of disturbed biological clocks, for which research will once again prove just how effective light therapy can be.