Effect of Light on Waking

• A study published in the February 2006 issue of "Sleep" investigated the sensitivity of light exposure on alertness, performance and waking. The researchers compared the effects of different wavelengths of light on patients during a 6.5-hour period of sleeping and found that the visualization of light is not the primary influence on sleep/wake cycles, but rather circadian rhythms influence the secretion of hormones, which initiates waking. However, the authors concluded that short-wavelength light can affect the production of two important hormones that control sleep/wake cycles, namely cortisol and melatonin.
  
  

Light Therapy for Sleep Disorders

• Visually impaired individuals offer an interesting subject group for researchers studying the relationship between light and sleep/wake cycles. A review article appearing in the February 2011 issue of "Clinical Therapeutics" investigated the effects of light on sleep disorders in visually impaired children. The authors conducted a review of published medical studies in several databases and found that none had documented benefits of light therapy on sleep rhythms. The authors concluded that not enough evidence exists to demonstrate the relationship of light exposure to waking and suggested that light along with behavioral and hormonal therapy need to be further investigated.
  
  

Light-sensitive Cells of the Retina

• To further investigate the effects of light and sleep/wake cycles, a group of researchers from Queensland University in Australia evaluated the relationship of light-sensitive cells of the retina and the circadian clock. They tested younger people with no history of sleep disorders by assessing their responses to light every hour for 24 hours in an environment with constant light. The participants in the study were controlled for factors that may influence sleep cycles, such as caffeine intake, activity, and temperature as well as other parameters. The study concluded that the exposure to light can influence the circadian rhythms through the nerve cells in the retina.
  
  

Irregular Sleep Patterns

• Circadian rhythms can be influenced by work schedules causing irregular sleep patterns regardless of light exposure. A study published in the March 2011 issue of "The Journal of Nursing Research" evaluated the effects of shift rotations on hormonal levels, sleep/wake cycles and levels of attention. The authors conducted a review of relevant medical research and found that a conflict existed between sleep/wake cycles and light/dark periods for those working night shifts in hospitals. They concluded that circadian disturbances led to interrupted sleep/wake cycles, mental acuity and general mood disorders due to these workers losing one to four hours of sleep per night as opposed to those working regular day shifts.