A little under two weeks ago, Amazon added a ‘Blue Shade‘ filter to its Fire tablets to help you fall asleep after nighttime reading. Not to be left behind, Google just essentially did the same for Play Books, calling it Night Light.
If you’re not caught up with your science, blue wavelengths of light tend to keep people awake, even after they’re done reading. Daylight contains a lot of blue, and smartphone displays are generally calibrated to match sunlight’s color temperature. By filtering out those colors (and essentially ending up with a pale orange/amber tint) you’re able to fall asleep more easily after reading.
As with other blue light filters, Night Light adapts your screen’s color temperature and brightness to your local time of day, which should lead to more comfortable nighttime reading. As the day progresses, you’ll see your screen’s color temperature become warmer.
To activate it, just open your book settings and click on the Night Light toggle. The app will remember the setting and automatically adjust itself afterwards.