Glossary · Vật lý
Visible light
The band of electromagnetic radiation the human eye can see, roughly 380 to 700 nanometres: violet at the short end, red at the long end. It is only a tiny slice of the full electromagnetic spectrum.
There is nothing physically special about 380 to 700 nm: it is not different in kind from other bands. What is special sits on the observer's side: the cone cells in the human eye are tuned to this narrow band alone, and the Sun is the dominant source of the visible light our eyes receive.
Within that band, wavelength sets the perceived colour: violet sits at the short-wavelength end, around 380 nm, red at the long-wavelength end, around 700 nm, and the other colours lie in between. White light is not a wavelength of its own but a mixture of many.
All electromagnetic radiation is light in the physical sense; only this very narrow part is light in the sense of being visible. The rest is still all around us, reachable only through instruments.