A recent study has showed that people's use of cell phones at night is making it harder for them to fall asleep. In fact the light emitted by the screen disturbs the production of melanin which is needed for a good night's sleep.
Manufacturers are trying to find a solution by making their smartphones less harmful to the eyes and to sleep itself.
Apple is introducing a "night shift" mode in its upcoming iOS update that will alter the light emitted by the screen during nighttime. Similarly Amazon is introducing "Blue Shade" to its Fire tablets in order to make them safer.