Blue light is a particular electromagnetic radiation of the visible spectrum, at a short wavelength, between 430 nanometers and 475 nanometers. 30% of people use digital devices for about 6 hours a day, 14% about 10 hours. Most light sources emit blue light, including smartphones and tablets, incandescent lamps, LCDs, and LEDs, found in ambient lighting systems and digital devices such as PC monitors , monitor TV.