Blue light is the visible light at end of the blue spectrum. Blue light is not as energetic as ultraviolet (UV) light, the main concern is that high doses of blue light may cause more cellular damage than longer wavelengths of visible light (which you see as the colors red through green). Furthermore, exposure to blue light has an impact on your sleep-wake cycle.
This increased blue light exposure from LED lights, television, smart phones, tablets, and laptop computers raises concerns about the effects it may have on the sleep-wake cycle and the damages to the eyes that it may have.
Considering the entire light spectrum, blue light has the shortest wavelengths that are detectable by the human eye. The sun has historically been the only source of blue light until the rise of technology. What was once natural blue light has turned into artificial that causes damages to the retina. This exposure to high levels of blue light is a cause for concern. Below is the light spectrum chart to show where blue light falls: