Until the advent of artificial lighting, the sun was the major source of lighting, and people spent their evenings in darkness. Now, in much of the world, evenings are illuminated, and we take our easy access to all those lumens pretty much for granted.
But we may be paying a price for basking in all that light. At night, light throws the body's biological clock—the circadian rhythm—out of whack. Sleep suffers. Worse, research shows that it may contribute to the causation of cancer, diabetes, heart disease, and obesity.
Avoid looking at bright screens beginning two to three hours before bed.
Reading from an iPad before bed not only makes it harder to fall asleep, but also impacts how sleepy and alert you are the next day, according to the research from Brigham and Women’s Hospital in Boston, Massachusetts.