Blue light is a type of light that not only comes from electronic devices such as LEDs, televisions, computers, and smartphones, but also from the sun that wakes us up each day. As you can imagine, exposure to light that keeps us awake is not beneficial when it's time to sleep; blue light suppresses melatonin and can affect sleep-wake cycles.
A study published in the Proceedings of the National Academy of Sciences found that people who read on electronic devices before bed experienced a delay in REM sleep and felt less alert the following day. If sleep-wake cycles are out of balance persistently, it can contribute to health conditions such as depression and metabolic disorders.
The best way to combat the adverse effects of blue light is to limit your use of electronic devices at night. Using display-adjusting apps and light-blocking glasses are one way to limit your exposure to blue light, but WebMD still recommends putting devices away for at least one hour before bedtime to get the best sleep.