Poor quality sleep is an epidemic in the modern world and light exposure is a big part of the problem. More specifically getting the wrong kinds of light at the wrong time of the day.
People today are surrounded by artificial blue light from many, many sources. Some of these sources include computer screens, televisions, smart phones and overhead lighting. Too much artificial blue light can not only cause digital eye strain and headaches during the day, in the evening it can make it harder to get to sleep and stay asleep. , ,  When we expose ourselves to this artificial blue light our bodies get the signal that it's time to be awake. This light throws the body's biological clock—the circadian rhythm—out of whack. Worse yet, research shows that it may contribute to the causation of cancer, diabetes, heart disease, and obesity. 
Red and near-infrared light are part of the electromagnetic spectrum, and more specifically, part of the spectrum of light emitted by the sun. These wavelengths of light are “bioactive” in humans.
Below is a chart outlining the electromagnetic spectrum: