It may be a placebo effect but I think I'm feeling different with them in
(more energetic, up beat, etc.)...

No, I don't think it is a placebo effect. Research has identified a condition
in northern climate dwellers called Seasonal Affective Disorder. it is a form
of depression caused by low light levels & short days. The recommended
treatment is spending time each day under full spectrum fluorescent lights. And
for years I thought it was the plants in the plant room that were cheering me
up!

Iris,
Central NY, Zone 5a, Sunset Zone 40
"The trouble with people is not that they don't know but that they know so much
that ain't so."
Josh Billings (Henry Wheeler Shaw), 1818-1885