Measurements include three periods of dark season when the sun does not rise from mid November to late January and two periods of midnight sun season when the sun does not set from mid May to late July. Results indicate a linear association between natural daylight exposure and sexual interest. Results followed latitudes, with more disturbance in the north and less in the south. No systematic pattern was found south of 62oN. SDI scores were higher at 67oN, 69oN and 70oN than at all other latitudes. 58oN mean hours of sleep was 7 hours.
Results indicate a possible delayed sleep phase syndrome during winter at northern latitudes.
Measurements include three periods of dark season with no sunrise from mid November to late January and two periods of midnight sun season with no sunset from mid May to late July. Preliminary results show a linear relationship between seasonal variation in day-light exposure and SDI scores, with less disturbances during summer than during winter. Results indicate a linear association between natural light exposure and sleep disturbance. Personality traits Personality traits in seasonal affective disorder. Data were collected through personal visits to each of the included colleges during one week in the middle of January.