title: Wake up time, light, and mood in a population sample age 40-64 years.
abstract: OBJECTIVE
  Concern that disturbances of sleep and light exposures at night might increase cancer risks have been expressed, but little actual exposure data has been collected. Measurements from a representative population sample were examined to understand the magnitude of in-bed light exposure at night and possible correlates.
  
  
  METHODS
  From 1990 to 1994, a home survey of sleep disorders among adults ages 40-64 was conducted in the City of San Diego California, using stratified representative sampling techniques. Along with questionnaires, sleep logs, and 3-night wrist activity and pulse oximetry measures, bedside illumination was measured with a computer recording system. Questionnaires included the CESD depression scale and a scale of symptoms typical of winter depression.
  
  
  RESULTS
  Complete data were available from 286 men and women, whose mean in-bed intervals averaged 7 hours and 42 minutes. The mean room illumination during the first part of the night was mean 12.7 lux (median 3.2 lux) and during the last 2 hours in bed averaged 28.7 lux (median 18.9 lux). Nocturnal light exposure was positively correlated with age, male gender, summer season, time in bed, wake-up time, and depressive symptoms.
  
  
  CONCLUSIONS
  Complex bi-directional interactions may take place between sleep disturbances, depression, time in bed, wake-up-time, and in-bed illumination. The most crucial light exposures appear to occur in the last 2 hours in bed, largely after dawn, so daylight exposure may be an important factor.
authors: Sleep Clinic Chofu, Tokyo, Japan.
authors: Takuro
authors: T
authors: Endo
authors: Department of Psychiatry, University of California, San Diego, CA, USA.
authors: Daniel F
authors: DF
authors: Kripke
authors: Department of Psychiatry, University of California, San Diego, CA, USA.
authors: Sonia
authors: S
authors: Ancoli-Israel
keywords: Circadian rhythm; Depression; Light; Photometry; Sleep