The short answer is that there is strong evidence that light affects mood and energy for people who have seasonal depression diagnosed as Seasonal Affective Disorder (SAD), it may help conventional depression, and probably gives a boost to anyone feeling the blues especially during the winter.
The best thing to do is to get outside more! It may help, however, to expose yourself to a lightbox for up to an hour a day. I know my own energy is low in the winter and that I feel better when I hike regularly (go figure). Be that as it may, I have a lightbox on my desk which I probably sit at most days for at least an hour. When my colleagues and I moved into our offices about four years ago we discussed which office we preferred. I chose the one with southern exposure. There is nothing like sitting at my desk, which faces the southern window, on a bright and sunny winter day. But on the gray days, the lightbox is a great help to me.
Mine is a goLITE, but honestly, I don’t know enough about lightboxes to endorse it. It was inexpensive but the light comes out blue which is kind of weird but I’m used to it. If you have a lightbox that you love and have done research on, please email me at firstname.lastname@example.org and I’ll check it out and post reviews in a blog post.
For now, here’s a great article from Time magazine on sunlight and mood.