The more megapixels the phones camera has, the better images you get, the dimmer the screen is, the better it's for your eyes; overnight charging harms the battery, smartphones can float !
Do not use your mobiles with low brightness. It will cause the following effects :
1. If you use mobile phones before bedtime, it will put an excessive strain to your eyes. It will first cause dryness in your eyes and ultimately leads to weak eyesight. You can even go blind if you continue using your mobiles on dim light.
2. It can damage your retinal cells and it may result in the muscular degeneration. Brain diseases might be caused with low brightness level of mobile phones. Blue light from your laptops and mobiles can lead to migraine.
3. Using mobiles on dim light for longer time during night can restrains the production of melatonin which controls the sleep-wake-cycle. It will make more difficult to fall asleep and you will find difficulty to wake up next day.