A reader asks:

 Does the changing length of day and the time of natural sunrise/sunset affect the optimum-time calculation for light therapy?


Only indirectly. Our internal circadian clock adjusts seasonally to the dynamically changing time of sunrise. Therefore, if you complete the Automated Morningness-Eveningness Questionnaire in the spring, you are likely to have a different score than if you take it in the winter. In general, people with SAD score lower — or show greater eveningness–in the winter than in the spring.