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 .
A Multicenter Study of the Light Visor for Seasonal Affective Disorder: No Difference in Efficacy Found Between Two Different Intensities
Fifty-five patients with winter seasonal affective disorder ( SAD ) were treated with a light visor , a newly developed portable light-delivery system , in a controlled parallel design . A dim ( 400 lux ) visor was compared with a bright ( 6000 lux ) visor for either 30 or 60 minutes in the morning for 1 week . Response rates for these two treatments were 36 % and 56 % , respectively ; the duration of treatment sessions did not affect outcome . There was no evidence that the brighter visor was superior in efficacy to the dimmer one . Significantly greater relapse occurred following withdrawal of the dimmer visor . Alterative explanations for these findings are that the light visor is acting as a placebo or that it is equally effective over a wide range of intensities
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 .