We have reached the point of a public health crisis with the rapid increase in mood disorders. Antidepressant usage has risen 65% over the last decade and a half with 16.5% of women now taking prescription antidepressants and countless others dealing with depression through self-medication.
Economically and physically this is taking a toll on our society.
While there are many factors that play into depression, one environmental cause that CAN BE FIXED is exposure to blue light at night.
Why would something so innocuous as watching TV or playing a video game on your iPad at night increase your risk for depression?
To answer that question, here is an explanation from a 2017 article from the Journal of Translational Psychology:
Exposure to light at night perturbs the circadian system because light is the major entraining cue used by the body to discriminate day and night. When exposure to light is mistimed or nearly constant, biological and behavioral rhythms can become desynchronized, leading to negative consequences for health. Mood disorders have long been associated with light and circadian rhythms. One example is seasonal affective disorder in which mood oscillates between dysthymia during the short day lengths of winter and euthymia during the long summer days. In fact, a striking number of mood disorders are either characterized by sleep and circadian rhythm disruption or precipitated by an irregular light cycle.
The study goes on to explain:
Circadian regulation permeates most systems believed to control mood, including limbic brain regions, monoamine neurotransmitters and the hypothalamic–pituitary–adrenal axis. 
Blue light (480 nm) specifically is your body's cue that it is daytime. It synchronizes your circadian rhythms. Prior to artificial light, this had worked for millions of years: the sun coming up each morning signals that it is daytime. The lack of light at night has signaled for the second half of the circadian cycle... until now.
The study above points to one mechanism of action for circadian regulation of mood through neurotransmitters. If you are of the same generation as me, the first thing that comes to mind for neurotransmitters may be the commercials for antidepressants that showed little circles flowing from one neuron to the next.
Monoamine oxidase A (MAOA) is an enzyme that is intimately involved in the regulation of the neurotransmitters dopamine, serotonin, and norepinephrine. (One class of antidepressants is MAO inhibitors.) This ties into circadian rhythms because the core circadian genes control the rhythm of MAOA production. When you mess with circadian rhythm, you mess with monoamine oxidase levels and thus with dopamine, serotonin, and norepinephrine.
Is this a huge change in neurotransmitter levels? Probably not for most people. We humans are a resilient bunch and get used to chronic environmental changes. But some people have genetic variants in either the core circadian genes (such as PER2) or in the gene that codes for MAOA. And those people may be less resilient, more likely to become depressed or anxious due to light at night.
Another example of circadian rhythm disruption causing depression can be seen when looking at melatonin levels, which are impacted by light at night. A recent study of psychiatric patients showed that study participants with lower levels of melatonin were at an increased risk higher depression score index. In other words, among this population of inpatient psychiatric hospital patients, low melatonin = high depression.
So if melatonin levels are connected to depression levels, can you just take a melatonin pill for depression? In our pharmaceutical laced world of a pill for every symptom, of course this is being investigated. There are currently ongoing clinical trials using melatonin as an antidepressant. A previous clinical trial in breast cancer patients did find that melatonin supplements decreased the risk of depression by 75%.
How does light tie into this? Blue light (480 nm) is the signal to shut down your body's melatonin production. A clinical trial using blue-light blocking glasses for a couple of hours before bed showed significant improvement for patients in the manic phase of bipolar disorder.
Let me sum all of this up:
1) Artificial blue light after the sun goes down is affecting our circadian rhythm and decreasing melatonin production.
2) If we block blue light at night either through wearing blue-blocking glasses or by switching out our home lighting, melatonin production will increase and our core circadian clock with stabilize.
3) For some, this will decrease depression and anxiety.