" The connection between darkness and depression has been well established in research. A study published on March 25, 2008, in the Proceedings of the National Academy of Sciences reveals the significant changes that light deprivation causes in the brain. The researchers called this mood suppression a “stress-free means of producing a depression.”

Principal investigator Gary Aston-Jones, now at the Medical University of South Carolina, said, “It might be particularly relevant to seasonal affective disorder, but we think that it is relevant to depression overall. "

― Cary G. Weldy , The Power of Tattoos: Twelve Hidden Energy Secrets of Body Art Every Tattoo Enthusiast Should Know