References on Light and the Biological Clock

Serotonin in the Spotlight. Nature 1997; 385:123
P.D. Penev, P.C. Zee, F.W. Turek.

"It raises the possibility that photic stimulation may, in a similar fashion, alter the functional status of serotonergic pathways outside our circadian model framework - changes which could have important implications for the use of light as a "drug" to alter neurochemical activity in the brain."

Effects of Tryptophan Depletion on Drug-Free Patients with Seasonal Affective Disorder During a Stable Response to Light Therapy. Archives of General Psychiatry 1997; 54:133-138A.
Neumeister, N. Praschak-Reider, B. Hebelmann, M. Rao, J. Gluck, S. Kasper.

The maintenance of light-therapy induced remission from depression in patients with seasonal mood cycles seems to depend on the functional integrity of the brain serotonin system. Our results suggest that the serotonin system may be involved in the mechanism of light therapy." Abstract