The spectrum of light is subdivided on the basis of wavelengths in the nanometer range. Different wavelength ranges can be defined, which have different properties. You can find the blue range between 380 - 500 nanometers. It appears as a blue color. Similar to UV light, which is harmful to the body, blue light has short waves and is very high in energy. Not so good.
Blue light has the evolutionary task of signaling the body to be awake when the sun is shining. Biochemical processes prevent the production of the sleep hormone melatonin.