As early as the mid-nineteenth century, scientists began to notice the electromagnetic waves in the shortwave direction of visible light in the whole electromagnetic spectrum and called the range between 10 and 400 nm the ultraviolet (UV) region. This region is divided into four parts: UVA (380–315 nm), UVB (315–280 nm), UVC (280–200 nm), and vacuum ultraviolet (VUV, 200–10 nm). Due to the Earth’s ozone layer’s absorption of ultraviolet light below 280 nm, the atmosphere contains almost no ultraviolet light below 280 nm; thus, this band of ultraviolet light is also called solar-blind light; this makes the communication accuracy in this band extremely high.