Light therapy

Ancient medical books are filled with recommendations in favor of getting enough light. For example, the ancient Ayurvedic physician Charaka who lived in the sixth century B.C., recommended sunlight to treat a variety of diseases. For thousands of years people revered the sun as a great healer and ancient cultures frequently worshiped the sun.

In 1980, A. J. Lewy and coworkers published an article in Science that ushered in the modern era of phototherapy. Lewy suggested that secretion of the hormone melatonin could be suppressed by exposing subjects to bright artificial. Melatonin is nicknamed "the chemical expression of darkness" and is secreted at night and to tell the body that it is time to sleep.

\We know that lack of sunlight can result in nutritional deficiencies. Without sunlight vitamin D cannot be metabolized in the human body. Many enzymes, hormones and vitamins need light for proper functioning.

In a study reported in the American Geriatrics Society, researchers wanted to find out "the effects of low-power light therapy on pain and disability in elderly patients with degenerative osteoarthritis of the knee." They have divided the patients into three groups. One group was treated with red light, one was treated with infrared light and the third group got no light therapy. Prior to the light therapy, the pain and disability was statistically similar among the three control groups. They found that pain reduction in the red and infrared groups after the treatment was more than 50%. Significant improvement was not found in the placebo group. The experiment showed that low-power light therapy is effective in relieving some pain.

How Does Light Affect The Human Functions?

Human beings are the product of habits and heritage. Before the advent of alarm clocks, many farmers woke up hearing the rooster crowing, announcing the arrival of morning. They milked their cows, worked in the farm and went to bed at night. There was no electricity. So, daylight announced the initiation and termination of many activities.

The problem is our modern system, with late shows and late night activities, does not allow enough time to sleep. People are influenced by the light. Light determines our sleep/wake cycle. In most animals and humans, the desire to sleep is brought on by secretion of a hormone called melatonin.

Statistics show that despite living and working in "closed structures," our bodies still respond to the external environment.  For example, surveys carried out in Germany, Sweden, and Scotland show that height and weight increase is more in the spring and early summer. In many countries the rate of conception peaks in the summer when the hours of daylight are longest. In numerous trials the seasons have been seen to influence the timing and duration of sleep, pain threshold, alertness, eating habits, mood, the onset of menstruation in women, and the desire for sexual activity.

Brain, Hormones, Biological Cycles and Clocks

In order to understand the mechanism of Seasonal Affective disorder and the effect of light on our mind, it is necessary to get an understanding of how our body and brain work. We will introduce some important terms in this section to augment our understanding.

Our brain manages a number of complicated body processes, breathing, digestion, circulation, growth, reproduction, and repair. The brain utilizes two separate systems to control these processes:  the nervous system and the endocrine system.

The nervous system is the fastest out of the two. To send a message fast, the brain uses the nervous system. The messages are generally brief (such as a few thousandths of a second). The nervous system employs electrical impulses that travel through nerve cells as fast as 650 feet (200 meters) per second.

The endocrine system sends most messages slowly. It uses hormones to produce more long lasting effects. Hormonal messages travel through the blood stream. It may take several hours or days to reach the destination or to effect a change. Endocrine system is a collection of ductless glands throughout the body that secrete hormones directly into the blood stream. These glands include the pituitary, thyroid, thymus, adrenals, pancreas, ovaries or testes, and many others. The function of these glands are to control the internal environment of the entire body.

It is the pineal's job to announce to the rest of the body that it is dawn or dusk, time for the body to be awake and alert, or time to prepare for bed and a rejuvenating sleep. This crucial signal sets complex processes into motion, a cycle that is designed to remain relatively regular and balanced. The circadian rhythm (see below for an explanation) lies at the heart of the state of internal balance and harmony we know of as health. When it becomes disrupted over a long period of time, there may be serious physical and psychological consequences.


Melatonin is produced by the pineal gland. Scientists believe that the pineal gland and melatonin are the body's primary timekeepers-its clock and calendar-imparting information about the time of day, season of the year, and phase of life to the brain and throughout the body. Melatonin is believed to influence the internal processes so that all of the body's systems work together, in coordination. Should this internal structure become disorganized in any way, the body becomes more susceptible to disease.

Melatonin is produced almost exclusively at night or in a light-free environment. (In fact, it is nicknamed "the chemical expression of darkness" by scientists because of its nocturnal habits.) Blood levels of melatonin are up to ten times greater at night than during the day.

In the morning, when we perceive that it is light, melatonin secretion ceases, which stimulates the production of other hormones and hence other body activities to begin. This orderly daily rhythm is of prime importance to our physical condition, intellectual capabilities, and emotional health.

The ways in which these seasonal patterns affect human behavior is under intense investigation. Some researchers believe that seasonal melatonin levels may help to explain Seasonal Affective Disorder.

Rhythms and Body Clock

Circadian Rhythm

From the Latin circa (about) dies (a day), the circadian rhythm is the twenty-four-hour cycle of light/dark, wakefulness/sleep to which most human physiologic processes are set. At regular intervals each day, the body tends to become hungry, tired, active, listless, energized. Body temperature, heart-beat, blood pressure, hormone levels, and urine flow rise and fall in this relatively predictable, rhythmic pattern - a pattern initiated and governed by exposure to sunlight and darkness.

Experiments where humans were placed in isolation chambers, cut off from all potential environmental cues, have shown that, in the absence of natural daylight, rhythms are still maintained. But in the absence of the daylight, the rhythms tend to deviate from 24 hours. For instance, the rhythms were found to expand to 24 to 30 hours, thus disrupting the biological processes over a long period of time.

The fact that animals and humans can continue to function according to daily and annual rhythms in the absence of external environmental stimuli means that animals and humans possess some kind of biological clock, which act as a backup mechanism in case it cannot get the proper stimuli from the natural events such as sunshine.

However, in the absence of natural light, our body clocks may lose or gain a little time. This in turn could lead to the desynchronization of different rhythms. For example, in the absence of sufficient environmental light the sleep-wake and associated rest-activity rhythms may lengthen to a cycle of between 30 and 48 hours, while the temperature rhythm may remain at a period of, say, 25 hours. Such desynchronization of the body's intricate rhythms is suspected to trigger problems: hormonal imbalances, sleep disorders, and mood disturbances.

Circannual Rhythm

Circannual rhythm is the annual or yearly cycle used by all living things.

Circaseptan Rhythm

Circaseptan rhythm is a seven-day cycle in which the biological processes of life, including disease and development, revolve. Many physicians believe that transplant patients tend to have more rejection episodes seven, fourteen, twenty-one, and twenty-eight days after surgery. They further believe that medications administered to the patients at particular times may be more effective than at other times. These are all related to the circaseptan rhythm.  

How does the brain know when it is light or dark?

Deep within the brain, inside the hypothalamus, lie two clusters of cells (i.e., neurons) called the suprachiasmatic nuclei (SCN). Each of these SCN is composed of more than 8,000 neurons. The SCN act as the body's circadian pacemaker. In mammals, the SCN appear to get their information from photoreceptors in the retina, which transmit signals about light and dark through the optic nerves to the hypothalamus. Once these messages enter the SCN, a series of physiological reactions takes place.

Light Therapy for Seasonal Affective Disorders

One of the most important applications of light therapy is in the treatment of Seasonal Affective Disorders (SAD). There is a large body of scientific evidence that points to the efficacy of light therapy for the treatment of SAD. What is not quite understood, yet, is how light treatment works.

Light Therapy Is not Always Safe

If you have an eye or skin condition which is affected by bright light, you should consult a doctor before embarking on light therapy. If you are suffering from disorders such as glaucoma, cataracts, retinal detachment, retinopathy, do not undergo the bright light treatment. The bright light could worsen the eye problem or cause a rash in a skin condition. If you suffer from hypertension, diabetes or have any history of eye disease in the family, seek medical advice before starting light therapy.

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Last modified: 08/06/08