<p>The targeted use of light - the light therapy - can contribute to wellbeing and health. This can counteract the negative effects of the living environment or personal development. For example, light helps with sleep disorders (such as shift work, jet lag), which are caused by a shift of the "internal clock" (circadian rhythm). Light therapy also helps with lack of motivation, especially in seasonally dependent depression, which occur in the dark winter months and is caused through the lack of natural daylight.</p>