Light boxes have been shown to help with seasonal depression, but should be used with caution in people with bipolar since it can provoke manic symptoms. I would recommend starting with a lower dose of light, perhaps 8-10 minutes, and slowly work your way up from there. Try increasing by 2 min every 3-4 days. I find my best balance is about 15 min. It may be less than the instructions tell you to use, but it addresses my depression without making me agitated. Good luck!
As it treats depression perhaps in some way it could activate mania as some other treatments do including medications and other treatments such as ECT that help on depression. Ask your psychiatrist if this is within potential and they could tell you what to do from there.