I bought one in October and have been using it daily, except for my recent trip to Central America where it was sunny and warm every day. I think it does me at least some good, because normally I get depressed in the late fall/early winter and I have not had that happen this year. I'm bummed about Christmas because it's my first one without my husband, but that's not depression. I also haven't experienced mania due to the light, so I think I'm safe to continue using it for the full 30 minutes each morning. Your mileage may vary.