http://articles.mercola.com/sites/articles/archive/2012/08/09/too-much-night-light-causes-depression.aspx?np=true

Even if the light is so dim that you can easily sleep through it, light pollution can prompt biological changes that have a very significant, and potentially serious, impact on your physical and mental health.

[snip]

“Exposure to artificial light at night (LAN) has surged in prevalence during the past 50 years, coinciding with rising rates of depression.”

The link could be due to the production of the hormone melatonin, which is interrupted when you’re exposed to light at night. There are many studies that suggest melatonin levels (and by proxy light exposures) control mood-related symptoms, such as those associated with depression — especially winter depression (aka, seasonal affective disorder, or SAD).

https://www.tumblr.com/drgrady/29558445854/too-much-light-at-night-may-lead-to-depression