What did strict study generally find about the effect of internet use on sleep?

It can lead to lack of sleep, depression, weight gain, lack of focus, and drowsy driving due to lack of sleep.

However, research has show LED lights (found in phone screens) suppress the production of a sleep hormone melatonin. Further more, most light bulbs are now florescent, because they are more efficient and put off more light. As far as I know; most phone manufactures still use LED lights. Hope this helped