Harvard Health Blog: Visible light includes a short segment of wavelengths tucked into the electromagnetic radiation spectrum.
In addition to helping us see, light also has nonvisual effects on the body, says Dr. Steven Lockley, a neuroscientist at the Division of Sleep and Circadian Disorders at Harvard-affiliated Brigham and Women’s Hospital.
During the day blue-enriched light is desirable, because it helps synchronize our circadian clocks to a 24-hour day. So, exposure to a regular light-and-dark cycle is vital to achieve and maintain good sleep.
Stimulation from certain wavelengths of blue light helps us stay alert, whether this comes from a natural source like the sun in daytime hours, or from electronic devices that emit blue light. While the stimulation is helpful during the day, at night it can interfere with sleep. Blue-light exposure in the evening — for example, binging a TV series on your laptop right before bed — will stimulate the melanopsin-containing cells and alert the brain, making it think it is daytime. That can make it harder to fall asleep and may affect the quality of your sleep.