Light-dependent effects on mood: Mechanistic insights from animal models.

Light is an important environmental stimulus that exerts a powerful influence on physiology and behavior across multiple timescales. Organisms have adapted to respond to the predictable 24-h light/dark cycle imposed by the solar day using this light information to appropriately time physiological and behavioral functions while acute changes in the light environment provide important salient cues to induce rapid responses. Variations in the light environment caused by seasonal changes in daylength as well as those prevalent in modern day life (artificial lighting, transmeridian travel) have made the light environment more irregular and unpredictable.