Seasonal Affective disorder or SAD is strongly related to seasonal changes and influences our circadian rhythm. SAD or commonly referred to as winter depression, is a mood disorder caused by the lack of light. It causes feelings of depression, and sleep disturbance.

Scotopic vision is the vision of the eye under low-light levels. The term comes from Greek skotos, meaning “darkness”, and -opia, meaning “a condition of sight”.

Under low lighting levels, the visual accuracy is poor and colour and details are less detectable. Scotopic vision is enabled exclusively through rod cells. As most of us live in urban environments we seldomly experience this type of lighting situation. This is due to the interference of light pollution which in urban environments does not allow us to experience real darkness.