Overall , both forms of preventive light therapy reduced the incidence of SAD numerically compared with no light therapy .
BACKGROUND Seasonal affective disorder ( SAD ) is a seasonal pattern of recurrent major depressive episodes that most commonly occurs during autumn or winter and remits in spring .
The prevalence of SAD ranges from 1.5 % to 9 % , depending on latitude .
The predictable seasonal aspect of SAD provides a promising opportunity for prevention .
This review - one of four review s on efficacy and safety of interventions to prevent SAD - focuses on light therapy as a preventive intervention .
Light therapy is a non-pharmacological treatment that exposes people to artificial light .
Mode of delivery ( e.g. visors , light boxes ) and form of light ( e.g. bright white light ) vary .
OBJECTIVES To assess the efficacy and safety of light therapy ( in comparison with no treatment , other types of light therapy , second-generation antidepressants , melatonin , agomelatine , psychological therapies , lifestyle interventions and negative ion generators ) in preventing SAD and improving patient-centred outcomes  among adults with a history of SAD .
Light therapy for seasonal affective disorder. The effects of timing.
BACKGROUND Sixty-eight patients with seasonal affective disorder participated in a 10,000-lux light treatment study in which two questions were addressed : do response rates differ when the light is applied at different times of the day and does short-term rank ordering of morning and evening light influence response rates ? METHOD Three groups of patients received a 4-day light treatment : ( I ) in the morning ( 8.00 - 8.30 a.m. , n = 14 ) , ( II ) in the afternoon ( 1.00 - 1.30 p.m. , n = 15 ) or ( III ) in the evening ( 8.00 - 8.30 p.m. , n = 12 ) . Two additional groups of patients received two days of morning light treatment followed by two days of evening light ( IV , n = 13 ) or vice versa ( V , n = 14 ) . RESULTS Response rates for groups I , II and III were 69 , 57 and 80 % respectively , with no significant differences between them . Response rates for groups IV and V were 67 and 50 % respectively ; this difference was not significant and these percentages did not differ significantly from those of groups I and III . CONCLUSIONS The results indicate that the timing of light treatment is not critical and that short-term rank ordering of morning and evening light does not influence therapeutic outcome
Overall , both forms of preventive light therapy reduced the incidence of SAD numerically compared with no light therapy .
BACKGROUND Seasonal affective disorder ( SAD ) is a seasonal pattern of recurrent major depressive episodes that most commonly occurs during autumn or winter and remits in spring .
The prevalence of SAD ranges from 1.5 % to 9 % , depending on latitude .
The predictable seasonal aspect of SAD provides a promising opportunity for prevention .
This review - one of four review s on efficacy and safety of interventions to prevent SAD - focuses on light therapy as a preventive intervention .
Light therapy is a non-pharmacological treatment that exposes people to artificial light .
Mode of delivery ( e.g. visors , light boxes ) and form of light ( e.g. bright white light ) vary .
OBJECTIVES To assess the efficacy and safety of light therapy ( in comparison with no treatment , other types of light therapy , second-generation antidepressants , melatonin , agomelatine , psychological therapies , lifestyle interventions and negative ion generators ) in preventing SAD and improving patient-centred outcomes  among adults with a history of SAD .