Aha. It's called Night shift then. I'm not a smartphone user myself. My mother was recently diagnosed with macular degeneration and cataracts, so there's been chatter among my siblings about blue light prevention. The eyeglasses I bought in February have a blue light coating. Blue light supposedly also reduces melatonin production which results in poor sleep.
Personally, I don't need an abundance of scientific evidence to enlighten me to the notion that staring at a video screen for hours a day is not ideal for personal health and wellness.