Ray has repeatedly warned against the exogenous supplementation with melatonin and has said that it is almost as dangerous as serotonin (of which melatonin is a metabolite). One of the main benefits of red light is that it sharply decreases melatonin synthesis, sometimes by as much as 90%. I don't know if red light also decreases serotonin, but at least it will prevent its increases due to the stress responses induced by darkness. One more confirmation of the darkness-stress mechanism.
http://www.ncbi.nlm.nih.gov/pubmed/5675470
"...The intraperitoneal administration of melatonin to rats caused an increase in brain serotonin concentration, especially in the midbrain. This effect could be demonstrated within 20 minutes of melatonin administration and was not associated with changes in norepinephrine concentration."
http://www.ncbi.nlm.nih.gov/pubmed/5675470
"...The intraperitoneal administration of melatonin to rats caused an increase in brain serotonin concentration, especially in the midbrain. This effect could be demonstrated within 20 minutes of melatonin administration and was not associated with changes in norepinephrine concentration."