I'm reading this Wikipedia article on light therapy and noticed a peculiar statement:
The production of the hormone melatonin, a sleep regulator, is inhibited by light and permitted by darkness as registered by photosensitive ganglion cells in the retina. To some degree, the reverse is true for serotonin, which has been linked to mood disorders.
If I read this correctly, when melatonin is suppressed, serotonin is released? This makes some sense. I'm interested if there is any scientific backing to serotonin being affected by light levels.