Light Therapy part 4

Overview of Light Therapy

Light Therapy

It is frequently argued that since many of us work in artificially lit buildings, we are seldom exposed to sufficient light. The human visual system adapts rapidly to changing intensities of illumination; consequently light encountered outdoors may not be perceived as orders of magnitude brighter than indoor illumination. Physiologically, however, humans respond quite differently to the higher levels of illumination provided by exposure to sunlight.
Most artificial lighting cannot replace the natural light. The reason for this is that the type of indoor lighting used is not of sufficient intensity to affect the hormonal mechanisms which control bodily rhythms. Intensity of light is measured in units called lux. One lux = the light received by the receptor at an intensity of one lumen per square meter. Thus the intensity of light at any point therefore is determined not only by the strength of the illumination source but also by how far it is from the source. The electric light used in most homes and workplaces rarely exceeds 500 lux. A sunny afternoon could be as much as 100,000 lux, even the cloudiest day is rarely below 10,000 lux. The therapeutic use of light therapy in SAD arose from basic research showing that exposure to room light (less than 500 lux) could alter circadian and seasonal rhythms in animals. Kripke et al (1978; 1981) had proposed circadian-rhythm hypotheses for non-seasonal depression and first published reports showing that bright light exposure could improve mood in patients with depression. It is assumed that the major circadian effects of light therapy, also called light treatment or phototherapy, are mediated via suppression of nocturnal melatonin secretion. In 1980, Lewy et al demonstrated that higher intensity light (>2,000 lux) was required to suppress human melatonin secretion. This observation led to the first controlled study of light therapy in SAD (Rosenthal et al, 1984). The efficacy of light therapy was clearly apparent, however, many sufferers found it difficult to allocate the four hours everyday that was needed for the light therapy to be effective. Additional studies were conducted to determine an optimum light therapy. It was found that, with a 10,000-lux light, sufferers only required 30 minutes of exposure per day to get effective alleviation from symptoms. However, the amount of light needed varies widely from individual to individual. The light treatment is most often done in the morning, but studies have suggested that either morning or evening light can help SAD (Terman et al 1998), though some patients suffer insomnia when they use the light in the evening. Early light therapy used special full spectrum lights, (so as to mimic sun light). More recently Lee et al (1998a) suggested that light of short to medium wavelengths (blue/green/yellow) seem to be essential for the therapeutic effect of light on SAD. Red wavelengths were relatively ineffective. Furthermore, ultraviolet (UV) waves do not seem to be essential for SAD symptom alleviation by artificial light. Therefore, the potentially harmful UV waves should be blocked in any clinical application of phototherapy for SAD. Recent studies suggest that regular fluorescent lights will work as well as full spectrum, allowing UV light (which can damage eyes and skin) to be filtered out. Studies show that it is advisable to buy a commercially built SAD light box to ensure the correct amount of light and to reduce isolated "hot spots" which could damage the eyes (Lam & Levitt, 1999). The most studied light device is the fluorescent SAD light box. The fact that the SAD light box has proven effective in almost every study, regardless of sample size, has placed the SAD light box as the "gold standard" light device. Other light devices include head mounted units, or incandescent light visors. Studies of the head mounted units have shown good clinical response rates (comparable to those of SAD light box studies) but the bright light conditions were no better than dim light, putting into question whether visors are superior to placebo. Dawn simulators are devices that slowly increase the room illumination while subjects are sleeping, to simulate a "summer dawn" during the winter. Early results suggest a beneficial effect of dawn simulators in SAD, but other studies show superiority of SAD light boxes over dawn simulators. Although efficacy has not been established for head mounted units and dawn simulators, these devices may be helpful for some patients when SAD light boxes are not available or not convenient. SAD symptoms typically begin to lift about a week after the start of light therapy. But they return shortly after discontinuing the treatment. As a result, experts urge people with SAD and S-SAD to persist with their light therapy treatment throughout the winter months.
Please note: If you are unsure of a SAD diagnosis or have contraindications then please consult with your GP/specialist before using a sad light box.


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