Light therapy is one of the main treatments for seasonal depression. It’s effective in improving symptoms and mood changes caused by SAD. The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) identifies SAD as a major depressive disorder with seasonal pattern. Light therapy for depression tries to replace the natural light that you miss during the winter months that can trigger your depression. Light therapy may work best when used with a special type of cognitive behavioral therapy or talk therapy. Known as CBT-SAD, it helps people cope and replace negative thoughts the winter season causes with more positive thoughts. Both CBT-SAD and light therapy are equally effective in improving SAD symptoms. But a long-term study following SAD patients for two winters found the positive effects of CBT-SAD seemed to last longer over time. So combining the two may help more.