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From SADwiki, the open SAD resource site for Seasonal Affective Disorder sufferers
According to research by Partonen & Lonnqvist (2000) bright light improves vitality and alleviates distress in healthy people. Partonen & Lonnqvist exposed office employees to bright light during winter and found that repeated bright-light exposure improved vitality and reduced depressive symptoms.
The benefit was observed not only in healthy subjects with season-dependent symptoms but also in those not having the seasonal variation. Bright-light exposure during winter therefore appears to be effective at improving the health-related quality of life and alleviating distress in healthy subjects. It is suggested that administration of bright light is a useful option to improve vitality and mood particularly among those working indoors in wintertime.
In the case of jet lag the individual is reacting to externally induced changes in the sleep-wake cycle. Travelling west to east over three or more time zones is the most difficult shift.
Large forced changes in the timing of sleep periods can lead to irritability and decreased alertness, several studies have shown that light therapy can be used very effectively to alleviate these symptoms (Smyth, 1990).
Shift workers often have symptoms of mild depression, fatigue, varying levels of sleep disorders and problems with attention and alertness. Studies have shown that these symptoms may also be significantly reduced through the use of light therapy (Czeisler et al, 1990; Stewart et al, 1995).