A reader asks:

Q: I use a light box on my desk at work all day during the fall and winter months. Should I limit the amount of time I keep it on? I was starting to get a headache the other day and wondered if I had left it on too long. Also, I have read that it is better to use the light box first thing in the morning. Is that as effective as using it throughout the workday?

Please spend some time on our website reading about the proper uses of light therapy. Then complete our Morningness-Eveningness Questionnaire (MEQ) for personalized feedback. Yes, light can be overdosed, and headache is one of the symptoms. You don’t state why you are using a light box at work, but it may be to avoid wintertime fatigue and depression. For best results, use our recommended light box at home as you wake up. If that is not enough, daytime supplementation at work may be helpful — but don’t overdo it!