EurekAlert! update

Hi, I know this may not be the most appropriate post to attach this comment to, but I have a question which might fall in your area of expertise:

Is it known whether Seasonal Affective Disorder is primarily a function of circadian rhythm upset, or is it a function of the decreased light intensity/total insolation in the winter independent of circadian rhythm issues? (Or is more complicated than that)?

I can think of a few experiments to test either one of these hypotheses (e.g., if it's a function of circadian rhythm upset you would expect a higher prevalence and degree of jetlag in SAD sufferers; while if it's a function of total insolation, you would expect something like a tanning booth to ameliorate the condition).

Have any such experiments been done?

It is definitely the effect of daylength on the clock (see this for a simple explanation). Other factors, e.g., light intensity, weather, can to some small extent modify the intensity of SAD.

Thank you for pointing out that article; now that you've mentioned it, I do seem to recall reading it back in December.

A follow-up question: Is it only the RGCs at play here, or could the exposure response of skin to near-UV light also play a role? If you were to set up a UV lamp to go off before dawn, for example, would this have an effect on SAD?

Not in humans.