Light, especially the blue light from electronic devices, disrupts sleep. Anyone who's experienced jet lag has become aware of our internal clock being thrown off. Our internal clock (or circadian rhythm) tells us when to wake, sleep, eat, recover, etc. Even without light or darkness, our body knows when it should be awake and when it should be asleep.
The eyes are the master of this clock because of their ability to sense light. When there are low levels of light, special nerve cells communicate to our brain that it's time to get ready for bed. The brain then releases chemicals to help us wind down and the pineal gland releases a hormone called melatonin.
Since light determines whether or not we get the message to secrete melatonin, it's easy to see how staring at an electronic screen, or simply being in a brightly-lit house in the evening, can be problematic. Your brain knows it's time for bed, but it's still waiting for darkness so it can cue the pineal gland to secrete melatonin and start down-regulating stress.
Blue light, from electronics in particular, disrupts melatonin production, which means we'll continue to suffer from poor sleep and a disrupted circadian cycle if smart phones, TVs, tablets, and computers continue to be our main source of entertainment in the evening. Unfortunately, white light from a light bulb or overhead fluorescent appears to be nearly as problematic as blue light as research reveals that short durations (1-2 hours) cause near-daytime melatonin levels after minimal exposure (around 500-1000lux).
How to Fix It Set your life to the sun. Expose yourself to lots of light in the morning and during the day, then turn it off in the evening and night. This includes blue light, which isn't a problem when melatonin levels are supposed to be low (during the day), and may in fact improve alertness and performance. Fight the light. Consider dimming the screen on your gadgets, or installing an app on your phone to tint your screen orange, can also help reduce the blue light emitted from your devices in the evening. This can help prevent suppression of melatonin and improve your sleep quality! Don't forget white light, though. Blocking it, or sticking to reddish light (candles are great for this), almost doubles melatonin levels!
If you struggle getting to sleep even once you're in bed, use these tips and hopefully they'll help you out!