While I believe that light therapy is beneficial, I'm also an advocate of good old vitamin D, in conjuction with it. According to the Mayo Clinic the following, so I am heartened to see I'm not entirely out to lunch:

"Seasonal affective disorder (SAD) is a form of depression that occurs during the winter months, possibly due to reduced exposure to sunlight. This condition is often treated with photo (light) therapy. In one study, a dose of 100,000 IU of vitamin D was found to be superior to light therapy in the treatment of SAD after one month. Further studies are necessary to confirm these findings."